AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 3 333-R340, Copyright © 1986 by American Physiological Society
Diluting segment in avian kidney. I. Characterization of transepithelial voltages
H. Nishimura, M. Imai and M. Ogawa
Renal tubules from the Japanese quail, Coturnix coturnix, were perfused in
vitro to characterize the transepithelial voltage (Vt). The thick limb (TL)
of the mammalian-type (MT) nephron showed Vt positive in the lumen (+9.1
+/- 0.7 mV, n = 35). The Vt decreased with increases in hydrostatic
perfusion pressure. Furosemide (lumen), Na cyanide (bath), and ouabain
(bath) reversibly reduced Vt. Removal of Cl or Na from the perfusate and
the bath decreased Vt of the TL from +10.3 +/- 3.0 to -0.3 +/- 0.3 (n = 5)
and from +7.4 +/- 1.5 to +1.2 +/- 0.2 mV (n = 8), respectively. The distal
tubule of the reptilian-type (RT) nephron showed two types of Vt: a
lumen-negative Vt in the late segment and a lumen-positive Vt in the early
segment that is in close contact with the parent glomerulus. Both voltages
were reversibly reduced by ouabain and Na cyanide. These results suggest
that in quail the TL of the MT nephron resembles the thick ascending limb
of the mammalian kidney with both Na and Cl required for generation of
luminal positivity and the distal tubule of the RT nephron appears
functionally heterogeneous.
