title: Bicarbonate transport by initial collecting tubule of aquatic- and land-phase amphibia.
abstract: 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.
mesh_terms: D000042:Absorption; D000557:Ambystoma / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport; D001696:Biomechanical Phenomena; D007474:Ion Exchange; D007684:Kidney Tubules / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology
chemical_list: D001639:Bicarbonates; D012964:Sodium