AJP - Regulatory, Integrative and Comparative Physiology, Vol 238, Issue 3 219-R223, Copyright © 1980 by American Physiological Society
Comparison of vertebrate salt-excreting organs
L. B. Kirschner
Many marine vertebrates must excrete NaCl against a substantial chemical
gradient to remain hypoionic to the environment. Salt secretion appears to
be mediated by "chloride cells" found in the gills of many fish or in salt
glands in elasmobranchs, reptiles, and birds. The ultrastructure of the
cells is similar in all animals possessing them, as is the composition of
the fluid they produce, and a common mode of function is suggested.
However, the extant flux-force data cannot be reconciled with a single
mechanism. They appear to suggest that various combinations of Na+-, K+-,
and Cl--transport systems can operate in different epithelia, and that
epithelial permeabilities may also differ. However, a solution
approximately seawater in monovalent ion concentrations is produced in
every case.
