AJP - Renal Physiology, Vol 253, Issue 2 310-F317, Copyright © 1987 by American Physiological Society
Bicarbonate transport by initial collecting tubule of aquatic- and land-phase amphibia
C. B. Yucha and L. C. Stoner
The rate of bicarbonate reabsorption (JHCO3) by in vitro initial collecting
tubules (ICT) from aquatic- and land-phase Ambystoma tigrinum was measured.
These animals intrinsically have different levels of plasma bicarbonate,
17.6 and 27.1 mM, respectively. ICT from both phases reabsorbed bicarbonate
at 11 pmol X mm-1 X min-1 when perfused in solutions equilibrated with 3%
CO2. The induction of metabolic acidosis or alkalosis had no effect on
JHCO3 by in vitro ICT. JHCO3 was abolished when ICT from aquatic animals
were perfused with solutions equilibrated with 1% CO2 and returned toward
the control value when 3% CO2 was reintroduced. The effect of plasma CO2
partial pressure on JHCO3 of the ICT may explain, at least in part, the
observed difference in plasma bicarbonate of the aquatic- and land-phase
animals. JHCO3 was reduced to 22% of control with amiloride and to 42% of
control when a Na+-free perfusate was used, but was insensitive to
ethoxzolamide. These data are consistent with the presence of a
sodium-proton exchanger on the apical membrane and a carbonic
anhydrase-independent mechanism of H+ secretion.
