AJP - Regu Fuel your research with LabChart
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Am J Physiol Regul Integr Comp Physiol 277: R1562-R1567, 1999;
0363-6119/99 $5.00
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Randall, D. J.
Right arrow Articles by Ip, Y. K.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Randall, D. J.
Right arrow Articles by Ip, Y. K.
Vol. 277, Issue 6, R1562-R1567, December 1999

The mudskipper, Periophthalmodon schlosseri, actively transports NH+4 against a concentration gradient

D. J. Randall1, J. M. Wilson1, K. W. Peng2, T. W. K. Kok2, S. S. L. Kuah2, S. F. Chew3, T. J. Lam2, and Y. K. Ip2

2 Department of Biological Sciences, National University of Singapore, Singapore 119260; 3 Biology Division, Faculty of Science, National Institute of Education, Nanyang Technological University, Singapore 259756; and 1 Department of Biology and Chemistry, City University of Hong Kong, Hong Kong, China


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Periophthalmodon schlosseri can maintain ammonia excretion rates and low levels of ammonia in its tissues when exposed to 8 and 30 mM NH4Cl, but tissue ammonia levels rise when the fish is exposed to 100 mM NH4Cl in 50% seawater. Because the transepithelial potential is not high enough to maintain the NH+4 concentration gradient between blood and water, ammonia excretion under such a condition would appear to be active. Branchial Na+-K+-ATPase activity is very high and can be activated by physiological levels of NH+4 instead of K+. Ammonia excretion by the fish against a concentration gradient is inhibited by the addition of ouabain and amiloride to the external medium. It is concluded that Na+-K+-ATPase and an Na+/H+ exchanger may be involved in the active excretion of ammonia across the gills. This unique ability of P. schlosseri to actively excrete ammonia is related to the special structure of its gills and allows the fish to continue to excrete ammonia while air exposed or in its burrow.

ammonia; Na+-NH+4-ATPase; ouabain; amiloride


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

THE MUDSKIPPER Periophthalmodon schlosseri is an amphibious teleost living on the mud flats of the mangrove swamps in Malaysia (10) and Singapore (9, 14). This fish is unusual in that it can tolerate much higher environmental ammonia levels than other teleost fish (23). Mudskippers, however, are not ureotelic (20, 21, 23), unlike the Lake Magadi tilapia, which tolerates high ammonia levels in the environment by converting accumulated ammonia to urea (24), which is then excreted. Mudskippers appear to have evolved alternate physiological modifications to tolerate such high environmental ammonia levels. These physiological mechanisms have presumably evolved to permit this animal to remain air exposed for prolonged periods of time in the mangrove swamps.

When mudskippers are on land, there is a significant decrease in ammonia excretion (12, 20, 21) into water on the body surface or into any puddle in which the animal sits. There is ammonia storage with the conversion of ammonia to amino acids (12, 21, 23). In addition, there appears to be a powerful glutamate dehydrogenase (GDH)-glutamine synthetase system to detoxify ammonia in the brain (11, 23). P. schlosseri can excrete some ammonia into air by volatilization, but this accounts for <3% of the normal rate of excretion when the animal is in water (Wilson et al. 26a). In addition, there may be some reduction in ammonia production, but this is not known.

P. schlosseri can tolerate ammonia concentrations of over 100 mM NH4Cl in their external environment (23). Experiments were undertaken to determine how these mudskippers are capable of existing in an environment containing such high ammonia concentrations. Are tissue ammonia levels elevated and is the animal able to tolerate the increase? If not, do levels remain the same because ammonia is either excreted or detoxified and then the product(s) stored or excreted? We examined the effects of high ammonia in the environment on tissue ammonia concentrations and rates of ammonia excretion. These results indicated that P. schlosseri can excrete ammonia against an electrochemical ammonium ion concentration gradient between the fish and the seawater. We then conducted a series of experiments to determine some of the mechanisms involved in this active ammonium ion excretion.


    MATERIALS AND METHODS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Specimens. P. schlosseri and Boleophthalmus boddaerti were collected along the Pasir Ris canal, Singapore. The fish were maintained and experimented on at 25°C in the laboratory as described by Peng et al. (23).

Study of the effects of ammonia exposure on tissue ammonia levels and plasma ionic concentrations. P. schlosseri were exposed to 50% seawater containing 10 mM Tris (pH 7.2) and 8 or 100 mM NH4Cl for 6 days, and the various tissues and organs were sampled and processed according to the methods of Peng et al. (23). Ammonia was determined according to the method of Kun and Kearney (15). The Na+ and Cl- concentrations in the plasma were determined using a Corning 410C flame photometer and Corning 925 chloride analyzer, respectively. Plasma osmolality was measured using a Wescor vapor pressure osmometer.

Study of the effects of ammonia exposure on ammonia excretion. P. schlosseri (45-65 g) were placed in conical flasks and left to stabilize for 12 h overnight in 50% artificial seawater, containing either 10 mM Tris (pH 7.2) or 10 mM AMP (pH 9.0), which was maintained at 25°C and not aerated. The volume of seawater inside the flask was five times the weight of the fish. Before experimentation the seawater in the flask was replaced with the same volume of Tris-50% seawater or Tris-50% seawater containing 8 mM NH4Cl (36 µM NH3) or Tris-50% seawater containing 30 mM NH4Cl (134 µM NH3). A water sample was taken immediately as the 0 h sample. After 24 h, a final water sample was taken. The 0 and 24 h water samples were analyzed for ammonia concentrations using a Tecator Aquatec analyzer equipped with an ammonia cassette. Solutions of NH4Cl were made at three different concentrations (30, 31, and 32 mM) to test the power of resolution of the Aquatec analyzer. The calculated concentrations (n = 5) from the readings obtained were 30.6 ± 0.26, 30.96 ± 0.34, and 32.12 ± 0.23 mM, respectively, which were significantly different from each other.

Determination of transepithelial potential. P. schlosseri were exposed to 50% seawater containing 10 mM Tris (pH 7.2) and 0, 10, 30, or 100 mM NH4Cl for 24 h, and the transepithelial potential was recorded according to the methods of Chew et al. (2) and Lee et al. (16).

Determination of branchial ATPase activities. Mudskippers were exposed to 50% seawater containing 10 mM Tris (pH 7.2) and 25°C for 6 days. Gill samples were collected according to the method of Zaugg (28) and stored at -80°C until analyzed. The gill samples in frozen buffer were allowed to thaw on ice and were processed for measurement of ATPase activity using the method of Chew et al. (2). The specific ATPase activity, expressed as micromoles inorganic phosphate released per milligram protein per hour, was obtained as the difference in activities assayed in the presence and absence of the specific ion(s), unless stated otherwise. Mg2+-ATPase activity was determined in the presence of 5 mM MgCl2. Na+-K+-ATPase was determined in the presence of 100 mM NaCl, 20 mM KCl, and 5 mM MgCl2, and its activity was obtained as the difference between enzyme activities assayed in the presence and absence of 1 mM ouabain. Na+-NH+4-ATPase was determined either in the optimized condition of 20 mM NH4Cl, 10 mM NaCl, and 5 mM MgCl2 or in a subsaturating condition of 1 mM NH4Cl, 10 mM NaCl, and 5 mM MgCl2. Its activity was obtained as the difference between enzyme activities assayed in the presence and absence of NaCl+NH4Cl. Na+-NH+4-ATPase activity was also assayed in the presence of 1 mM ouabain to estimate its ouabain sensitivity.

Study of the effects of ouabain, amiloride, and KNO3 on ammonia excretion. P. schlosseri were placed in conical flasks and left to stabilize for 12 h overnight in 50% artificial seawater maintained at 25°C. Before experimentation, the seawater inside the flask was replaced and the volume of water was five times the weight of the fish. Ammonia excretion rate was monitored for 3 h as stated above. Then the seawater was drained and an equal volume of 50% seawater containing 0.1 or 0.01 mM ouabain or 0.1 mM amiloride or 100 mM KNO3 was added. Ammonia excretion rate was monitored for another 3 h. The fish were allowed to recover in fresh 50% seawater for 3 h before the final determination of ammonia excretion rate. To study if ouabain had any effect on the active excretion of ammonia, P. schlosseri were exposed to Tris-50% seawater at pH 7 containing 2 mM NH4Cl or 2 mM NH4Cl plus 0.1 or 0.01 mM ouabain and ammonia excretion was monitored for 3 h as stated above. After 3 h, the fish were killed and the blood was collected for the determination of plasma ammonia concentration.

Results are presented as means ± SE. Student's t-test and one-way analysis of variance followed by Duncan's multiple-range test were used to compare differences where applicable. Differences with P < 0.05 were regarded as statistically significant.


    RESULTS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Fish exposed to 8 mM NH4Cl (36 µM NH3) in 50% seawater at pH 7.2 showed no increase in tissue ammonia concentration after 6 days exposure (Table 1), and only when exposed to 100 mM NH4Cl (446 µM NH3) for 6 days was there an accumulation of ammonia in muscle, liver, brain, and plasma (Table 1). Ammonia excretion was maintained at control rates when fish were exposed to up to 30 mM NH4Cl in 50% seawater at pH 7.2 for 24 h (Fig. 1). P. schlosseri maintained ammonia excretion in 2 mM NH4Cl in 50% seawater at pH 9.0, but fish exposed to 8 mM NH4Cl at pH 9 died within 2 h, presumably due to rapid NH3 entry resulting from elevated NH3 levels in this alkaline water.

                              
View this table:
[in this window]
[in a new window]
  		Table 1.   Concentrations of ammonia in muscle, liver, brain and plasma of P. schlosseri exposed to 8 mM NH4Cl (36 µM NH3) and 100 mM NH4Cl (446 µM NH3) for 6 days



View larger version (21K):
[in this window]
[in a new window]
  		Fig. 1.   Active excretion of ammonia by P. schlosseri against 8 mM NH4Cl or 30 mM NH4Cl leading to increases in ammonia concentration (mM ± SE, n = 3) in ambient 50% seawater containing 10 mM Tris (pH 7.2). Inset represents changes in ammonia concentrations in external media containing 0, 8, or 30 mM NH4Cl.

The transepithelial potential of P. schlosseri in ammonia-free 50% seawater was 10.28 ± 0.15 mV, positive inside (n = 6), and it was unaffected by exposure to 10 mM (10.07 ± 0.15 mV, n = 6) or 30 mM NH4Cl (9.50 ± 0.36 mV, n = 3). When the fish was exposed to 100 mM NH4Cl, however, the potential decreased to 6.47 ± 0.29 mV (n = 3).

Activity of Na+-K+-ATPase from the gills of P. schlosseri was significantly higher than that in another mudskipper, B. boddaerti (Table 2). P. schlosseri gills showed high reactivity to fluorescent tagged mouse monoclonal antibodies directed against the alpha -subunit of chicken Na+-K+-ATPase; the fluorescence was located on the basolateral border, but not the apical region, of the gill cells. Activities of gill Na+-NH+4-ATPase and Na+-K+-ATPase were comparable, and both were inhibited by ouabain. The ATPase activity was less, but still significant, when measured in the presence of 1 mM NH+4.

                              
View this table:
[in this window]
[in a new window]
  		Table 2.   Specific activities of ATPase activated by Mg2+, Na+ + K+, or Na+ + NH+4 from gills of P. schlosseri and B. boddaerti

In the intact animal, ouabain (0.1 mM) did not affect ammonia excretion by P. schlosseri in seawater containing only low levels of ammonia when, presumably, ammonia excretion can be maintained by diffusion of NH3 from the fish into the water (data not shown). Inhibition of ammonia excretion (Fig. 2A) and accumulation of ammonia in the plasma (Fig. 2B) were observed when ouabain was added to the seawater containing 2 mM NH4Cl, and NH3 diffusion was from the water into the fish. Under these conditions ammonia excretion is presumably maintained by active excretion of ammonium ions via Na+- NH+4-ATPase, which can be inhibited by ouabain. Without this pump there is no mechanism in place to remove the ammonia from the blood against a gradient, resulting in its accumulation.


View larger version (20K):
[in this window]
[in a new window]
  		Fig. 2.   Ouabain inhibited active excretion of ammonia by P. schlosseri against 2 mM NH4Cl in 50% seawater. A: ammonia excretion rate (µmol · kg fish-1 · h-1 ± SE, n = 5) of fish in 2 mM NH4Cl or 2 mM NH4Cl + 0.1 mM ouabain. * Significant difference from control value (P < 0.05). B: ammonia concentration (mM ± SE) in plasma of fish after 3 h of exposure to 0 mM NH4Cl (n = 6), 2 mM NH4Cl + 0.01 mM ouabain (n = 6), or 2 mM NH4Cl + 0.1 mM oubain (n = 5). "b", Significantly different from "a" (P < 0.05)

Addition of amiloride to the seawater resulted in the inhibition of ammonia excretion by P. schlosseri (Fig. 3). KNO3 (100 mM), however, had no clear action on ammonia excretion, indicating that V-ATPases may have little involvement in ammonia excretion in this fish (data not shown). There was an increased accumulation of Na+ in the plasma of P. schlosseri with increased external ammonia concentration (Table 3).


View larger version (13K):
[in this window]
[in a new window]
  		Fig. 3.   Amiloride (0.1 mM) inhibited rate of ammonia excretion (µmol · kg fish-1 · h-1 ± SE, n = 6) by P. schlosseri in 50% seawater. Ammonia excretion was measured each hour during control and amiloride exposure periods and for 3 hours of recovery. "b", Significantly different from "a" (P < 0.05); "ab", not significantly different from "a" or "b".


                              
View this table:
[in this window]
[in a new window]
  		Table 3.   Plasma osmolality and concentrations of Na+ and Cl- in P. schlosseri exposed to 8 mM NH4Cl (36 µM NH3) and 100 mM NH4Cl (446 µM NH3) for 6 days


    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

It would appear that when P. schlosseri is in water containing NH4Cl, ammonia entering the fish is either stored or excreted to keep tissue levels stable. Ammonia excretion was maintained when the fish was exposed to up to 30 mM NH4Cl for 24 h, and tissue ammonia levels were unchanged even after exposure to 8 mM NH4Cl for 6 days; ammonia levels only increased after 6 days exposure to 100 mM NH4Cl, indicating that storage of ammonia only plays a role when the fish is exposed to very high ammonia levels. Storage of ammonia as free amino acids in several tissues and as glutamine in the brain has been observed in these fish exposed to 100 mM NH4Cl (23). At lower environmental ammonia levels, ammonia accumulation is prevented by excretion. P. schlosseri is able to maintain ammonia excretion in 2 mM NH4Cl, 50% seawater, even at pH 9.0, indicating that back diffusion of NH3 from the water may be low, either because the water in contact with the gills is acidified and/or because the body surface may have a low NH3 permeability. In fact, a combination of the two is probable. The body surface, which is normally at seawater pH, may have a low NH3 permeability, whereas the water in contact with the gills is usually acidified (26a). A gill epithelium with high ammonia permeability but an acidified water boundary layer would allow NH3 excretion by diffusion when water ammonia levels were low and avoid the cost of actively excreting ammonium ions under these conditions.

Because the excretion rate of ammonia was constant and independent of the external ammonia concentration (Fig. 1) and tissue ammonia levels were unchanged when exposed to 8 mM NH4Cl, it can be assumed that the efflux of ammonia was increased to offset any increase in ammonia influx. Under all conditions of exposure to elevated levels of ammonia in the water >2 mM NH4Cl, both the NH+4 and NH3 levels in the external media were higher than those in the blood. Because, under these conditions, the transepithelial potential was not sufficient to offset the NH+4 gradient, excretion of ammonia by P. schlosseri must be active, presumably in the form of ammonium ions.

It is highly probable that the Na+-K+-ATPase and Na+-NH+4-ATPase activities measured in vitro in P. schlosseri gills were, in fact, due to the same transporter. The activities were similar and both were inhibited by ouabain. Thus it would appear that there is a substitution of NH+4 for K+ in the Na+-K+-ATPase in P. schlosseri gills. K+ and NH+4 have a similar hydrated radius, and it has been shown that these two ions can share transport pathways in many mammalian renal and nonrenal cell types, competing for binding sites on Na+-K+-ATPase (26). NH+4 substitution for K+ in Na+-K+-ATPase has been proposed as a method of branchial ammonia excretion in fish (4, 6), and NH+4 can be a more effective counter ion for Na+-K+-ATPase than K+ (19). In our experiments, ouabain added to the water inhibited ammonia excretion. On the basis of immunoreactivity to the alpha -subunit, the Na+-K+-ATPase in P. schlosseri gills appears to have a basolateral location (Wilson, unpublished data). Ouabain can penetrate cell membranes, if somewhat slowly. Thus we suggest that ammonium ions are removed from the blood into the gill epithelium by a basolateral Na+-K+ (NH+4)-ATPase.

How then are ammonium ions moved across the apical surface and out of the gills? Amiloride inhibition of ammonia excretion indicates that an Na+/H+ exchanger may be involved in ammonia excretion. Substitution of NH+4 for H+ has been proposed as a method of branchial ammonia excretion across the apical surfaces of the gills in fish (1). There are at least four Na+/H+ exchanger (NHE-1 to -4) subtypes in the mammalian renal tubule (17, 22). Kinsella and Aronson (13) documented the interaction of NH+4 and the Na+/H+ exchanger in the renal microvillus membrane, but their study did not specify if this interaction exists in all isoforms. For the proposed mechanism of ammonia excretion in P. schlosseri mentioned above, the Na+/H+ (NH+4) exchanger would have to be located on the apical surface. NHE-2 and NHE-3 are located on the apical membrane in the mammalian kidney and intestine (8). NHE-2 and NHE-3 differ in their sensitivity to amiloride. NHE-2 can be inhibited by amiloride; however, NHE-3 is known as the "amiloride-resistant" isoform (25, 27), but it is still inhibited by the level of amiloride used in this study. NHE-3 has been shown to be involved in transepithelial Na+ absorption; however, the function of NHE-2 is still not clear in mammals (8, 25). Thus the Na+/H+ exchangers in the gill mitochondrial rich cells of P. schlosseri may be similar to either the NHE-2 or NHE-3 isoform of mammals. Recent studies have indicated the presence of the NHE-1 isoform in the marine long-horned sculpin and the winter flounder (5, 7). Claiborne et al. (3) have detected the presence of an NHE-2 isoform in the marine long-horned sculpin.

This proposed mechanism for actively excreting ammonium ions via a basolateral Na+-K+ (NH+4)-ATPase and an apical Na+/H+ (NH+4) exchanger could also result in the accumulation of Na+ in the blood. Thus the observed sodium accumulation in the blood (Table 3) with increasing environmental NH4Cl levels is consistent with the proposed model for active ammonium ion excretion.

The gills of P. schlosseri are unique in having intrafilamentous interlamellar fusion (18). The resulting interlamellar spaces hold water and may help to prevent desiccation of the gill epithelium while the fish is out of water (Wilson et al. 26a). During a terrestrial excursion, as ammonia accumulates in this restricted interlamellar water space, passive diffusion of NH3 would diminish and NH+4 would have to be actively excreted into these interlamellar spaces to maintain ammonia excretion. Such an adaptation allows P. schlosseri to use amino acids as a source of energy (9) and maintain high levels of activity while out of water (14). In addition, burrow water may contain high ammonia levels and the fish could still excrete ammonia into this water while in the burrow. The ammonia concentration collected at a depth of 0.3 m from the burrows of P. schlosseri and B. boddaerti were found to be 2.02 and 1.08 mM, respectively, during nonbreeding seasons (Ip, Chew, and Randall, unpublished data). Because mudskippers have the unique behavior of taking care of the developing embryos in their burrows, the ammonia level in the burrow water during such a period can be expected to be even higher.

In conclusion, it appears that P. schlosseri is able to tolerate high environmental ammonia concentrations by actively excreting ammonium ions across the gills, thereby maintaining low tissue ammonia concentrations.

Perspectives

This is the first report of active ammonium ion excretion in fish. Active excretion of ammonia allows this mudskipper (Periophthalmodon schlosseri) to maintain ammonia excretion when exposed in air or to high ambient ammonia levels in water. This occurs when the animal is in its seawater-filled burrow, which is high in ammonia. Ammonium ions are excreted across the gills. The mechanisms involved appear to be similar to that reported in the mammalian kidney, namely a basolateral Na+-K+ (NH+4)-ATPase coupled to an apical Na+/H+ (NH+4) exchanger. This is further evidence that much of the evolution of ion regulatory processes found in vertebrates occurred in aquatic ancestors. The major change that occurred with the evolution of terrestrial forms was a shift in location from gills to kidney; the basic processes were already in place.


    FOOTNOTES

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Address for reprint requests and other correspondence: D. Randall, Dept. of Zoology, Univ. of British Columbia, 6270 Univ. Blvd., Vancouver, British Columbia, Canada V6T 1Z4 (E-mail: randall{at}zoology.ubc.ca).

Received 26 January 1999; accepted in final form 21 July 1999.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

1.   Cameron, J. N. Responses to reversed NH3 and NH+4 gradients in a teleost (Ictalurus punctatus), an elasmobranch (Raja erinacea), and a crustacean (Callinectes sapidus): evidence for NH+4/H+ exchange in the teleost and the elasmobranch. J. Exp. Zool. 239: 183-195, 1986[Medline].

2.  Chew, S. F., E. Goh, C. B. Lim, and Y. K. Ip. Cyanide exposure affected the production and excretion of ammonia in the mudskipper Boleophthalmus boddaerti. Comp. Biochem. Physiol. C Pharmacol. Toxicol. 441-448, 1998.

3.   Claiborne, J. B., C. R. Blackston, K. P. Choe, D. C. Dawson, S. P. Harris, L. A. Mackenzie, and A. I. Morrison-Shetlar. A mechanism for branchial acid excretion in marine fish: identification of multiple Na+/K+ antiporter (NHE) isoforms in gills of two seawater teleosts. J. Exp. Biol. 202: 315-324, 1999[Abstract].

4.   Claiborne, J. B., D. H. Evans, and L. Goldstein. Fish branchial Na+/NH+4 exchange is via basolateral Na+,K+-activated ATPase. J. Exp. Biol. 96: 431-434, 1982[Free Full Text].

5.   Claiborne, J. B., E. Perry, S. Bellows, and J. Campbell. Mechanisms of acid-base excretion across the gills of a marine fish. J. Exp. Zool. 279: 509-520, 1997.

6.   Evans, D. H., and J. N. Cameron. Gill ammonia transport. J. Exp. Zool. 239: 17-23, 1986.

7.   Harris, S. P., J. B. Claiborne, J. Pouyssegur, and D. C. Dawson. Transcripts homologous to Na/H antiporter isoform, NHE-1, in mRNA from the long horned sculpin (Myoxocephalus octodecimspinous) and winter flounder (Pseudopleuronectes americanus). Bull. Mt. Desert Island Biol. Lab. 32: 128-130, 1993.

8.   Hoogerwerf, W. A., S. C. Tsao, O. Devuyst, S. A. Levine, C. H. C. Yun, J. W. Yip, M. E. Cohen, P. D. Wilson, A. J. Lazenby, C. M. Tse, and M. Donowitz. NHE2 and NHE3 are human and rabbit intestinal brush-border proteins. Am. J. Physiol. 270 (Gastrointest. Liver Physiol. 33): G29-G41, 1996[Abstract/Free Full Text].

9.   Ip, Y. K., C. Y. Lee, S. F. Chew, W. P. Low, and K. W. Peng. Differences in responses of two mudskippers to terrestrial exposure. Zool. Sci. 10: 511-519, 1993.

10.   Ishimatsu, A., Y. Hishida, T. Takita, T. Kanda, S. Oikawa, T. Takeda, and K. H. Khoo. Mudskippers store air in their burrows. Nature 391: 237-238, 1998.

11.   Iwata, K. Nitrogen metabolism in the mudskipper, Periophthalmus cantonensis: changes in free amino acids and related compounds in various tissues under conditions of ammonia loading, with special reference to its high ammonia tolerance. Comp. Biochem. Physiol. A Physiol. 91A: 499-508, 1988.

12.   Iwata, K., I. Kakuta, M. Ikeda, S. Kimoto, and N. Wada. Nitrogen metabolism in the mudskipper, Periophthalmus cantonensis: a role of free amino acids in detoxication of ammonia produced during its terrestrial life. Comp. Biochem. Physiol. A Physiol. 68A: 589-596, 1981.

13.   Kinsella, J. L., and P. S. Aronson. Interaction of NH+4 and Li+ with the renal microvillus membrane Na+-H+ exchanger. Am. J. Physiol. 241 (Cell Physiol. 10): C220-C226, 1981[Abstract/Free Full Text].

14.   Kok, W. K., C. B. Lim, T. J. Lam, and Y. K. Ip. The mudskipper Periophthalmodon schlosseri respires more efficiently on land than in water and vice versa for Boleophthalmus boddaerti. J. Exp. Zool. 280: 86-90, 1998.

15.   Kun, E., and E. B. Kearney. Ammonia. In: Method of Enzymatic Analysis, edited by H. U. Bergmeyer, and K. Gawehn. New York: Academic, 1974, vol. 14, p. 1802-1806.

16.   Lee, C. G. L., W. P. Low, T. J. Lam, A. D. Munro, and Y. K. Ip. Osmoregulation in the mudskipper Boleophthalmus boddaerti. II. Transepithelial potential and hormonal control. Fish Physiol. Biochem. 9: 69-75, 1991.

17.   Levine, S. A., M. H. Montrose, C. M. Tse, and M. Donowitz. Kinetics and regulation of three cloned mammalian Na+/H+ exchangers stably expressed in a fibroblast cell line. J. Biol. Chem. 268: 25527-25535, 1993[Abstract/Free Full Text].

18.   Low, W. P., D. J. W. Lane, and Y. K. Ip. A comparative study of terrestrial adaptation of the gills in three mudskippers---Periophthalmus chrysospilos, Boleophthalmus boddaerti and Periophthalmodon schlosseri. Biol. Bull. 175: 434-438, 1988[Abstract/Free Full Text].

19.   Mallery, C. H. A carrier enzyme basis for ammonia excretion in teleost gill. NH+4 stimulated Na-dependent ATPase activity in Opsanus beta. Comp. Biochem. Physiol. A Physiol. 74A: 889-897, 1983.

20.   Morii, H. Changes with time of ammonia and urea concentrations in the blood and tissue of mudskipper fish, Periophthalmus cantonensis and Boleophthalmus pectinirostris kept in water and on land. Comp. Biochem. Physiol. A Physiol. 64A: 235-243, 1979.

21.   Morii, H., K. Nishikata, and O. Tamura. Ammonia and urea excretion from the mudskipper fishes Periophthalmus cantonensis and Boleophthalmus pectinirostris transferred from land to water. Comp. Biochem. Physiol. A Physiol. 63A: 23-28, 1979.

22.   Paillard, M. Na+/H+ exchanger subtypes in the renal tubule: function and regulation in physiology and disease. Exp. Nephrol. 5: 277-284, 1997[Medline].

23.   Peng, K. W., S. F. Chew, C. B. Lim, T. W. K. Kok, S. S. L. Kuah, and Y. K. Ip. The mudskipper Periophthalmodon schlosseri and Boleophthalmus boddaerti can tolerate environmental ammonia of 446 µM and 36 µM, respectively. Fish. Physiol. Biochem. 19: 59-69, 1998.

24.   Randall, D. J., C. M. Wood, S. F. Perry, H. Bergman, C. M. O. Maloiy, T. M. Mommsen, and P. A. Wright. Urea excretion as a strategy for survival in a fish living in a very alkaline environment. Nature 337: 165-166, 1989[Medline].

25.   Tse, C. M., S. A. Levine, C. H. C. Yun, S. R. Brant, J. Pouyssegur, M. H. Montrose, and M. Donowitz. Functional characteristics of a cloned epithelial Na+/H+ exchanger (NHE3): resistance to amiloride and inhibition by protein kinase C. Proc. Natl. Acad. Sci. USA 90: 9110-9114, 1993[Abstract/Free Full Text].

26.   Wall, S. M. Ammonia transport and the role of Na+,K+-ATPase. Miner. Electrolyte Metab. 22: 311-317, 1996[Medline].

26a.  Wilson, J. M., T. W. K. Kok, D. J. Randall, W. A. Vogl, and K. Y. Ip. Fine structure of the gill epithelium of the terrestrial mudskipper, Periophthalmodon schlosseri. Cell Tissue Res. In press.

27.   Yu, F. H., G. E. Shull, and J. Orlowski. Functional properties of the rat Na/H exchanger NHE-2 isoform expressed in Na/H exchanger deficient Chinese hamster ovary cells. J. Biol. Chem. 268: 25536-25541, 1993[Abstract/Free Full Text].

28.   Zaugg, W. S. A simplified preparation for adenosine triphosphatase determination in gill tissue. Can. J. Fish. Aquat. Sci. 39: 215-217, 1982.

Am J Physiol Regul Integr Compar Physiol 277(6):R1562-R1567
0002-9513/99 $5.00 Copyright © 1999 the American Physiological Society


This article has been cited by other articles:


Home page
 Am. J. Physiol. Gastrointest. Liver Physiol.Home page
R. T. Worrell, L. Merk, and J. B. Matthews
Ammonium transport in the colonic crypt cell line, T84: role for Rhesus glycoproteins and NKCC1
Am J Physiol Gastrointest Liver Physiol, February 1, 2008; 294(2): G429 - G440.
[Abstract] [Full Text] [PDF]

Home page
 Physiol. GenomicsHome page
C. M. Nawata, C. C. Y. Hung, T. K. N. Tsui, J. M. Wilson, P. A. Wright, and C. M. Wood
Ammonia excretion in rainbow trout (Oncorhynchus mykiss): evidence for Rh glycoprotein and H+-ATPase involvement
Physiol Genomics, November 14, 2007; 31(3): 463 - 474.
[Abstract] [Full Text] [PDF]

Home page
 Physiol. Rev.Home page
D. H. Evans, P. M. Piermarini, and K. P. Choe
The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and Excretion of Nitrogenous Waste
Physiol Rev, January 1, 2005; 85(1): 97 - 177.
[Abstract] [Full Text] [PDF]

Home page
 J. Exp. Biol.Home page
D. Weihrauch, A. Ziegler, D. Siebers, and D. W. Towle
Active ammonia excretion across the gills of the green shore crab Carcinus maenas: participation of Na+/K+-ATPase, V-type H+-ATPase and functional microtubules
J. Exp. Biol., September 15, 2002; 205(18): 2765 - 2775.
[Abstract] [Full Text] [PDF]

Home page
 J. Exp. Biol.Home page
N. T. Frick and P. A. Wright
Nitrogen metabolism and excretion in the mangrove killifish Rivulus marmoratus I. The influence of environmental salinity and external ammonia
J. Exp. Biol., January 1, 2002; 205(1): 79 - 89.
[Abstract] [Full Text] [PDF]

Home page
 J. Exp. Biol.Home page
A. Shingles, D. J. McKenzie, E. W. Taylor, A. Moretti, P. J. Butler, and S. Ceradini
Effects of sublethal ammonia exposure on swimming performance in rainbow trout (Oncorhynchus mykiss)
J. Exp. Biol., January 8, 2001; 204(15): 2691 - 2698.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Randall, D. J.
Right arrow Articles by Ip, Y. K.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Randall, D. J.
Right arrow Articles by Ip, Y. K.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online