Effects of intracellular calcium on proximal bicarbonate absorption.
Using in vivo microperfusion in the proximal convoluted tubule (PCT) of the Munich-Wistar rat, we assessed the impact of raising intracellular calcium concentration on bicarbonate transport and its regulation by angiotensin II. Luminal perfusion with the calcium ionophore A23187 caused a dose-dependent increase in S1 PCT bicarbonate absorption, with a maximal change of 60 peq.mm-1.min-1. Subsequent addition of phorbol ester (PMA) after A23187 further increased transport but to a level no higher than previously shown with PMA alone, and A23187 was nonstimulatory when added after PMA. These results suggest that intracellular calcium affects the same pathway as protein kinase C in stimulating proximal acidification. Pretreatment with A23187 (+/- PMA) attenuated by approximately one-third the bicarbonate absorptive response in the S1 PCT usually observed after angiotensin II administration. A23187 had similar actions, but of smaller magnitude, in the S2 PCT. In conclusion, a rise in intracellular calcium increases bicarbonate absorption in the S1 and S2 PCT in vivo.
Liu
F Y
FY
Cardiovascular Research Institute, University of California, San Francisco.
Cogan
M G
MG
D000042:Absorption; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000493:pharmacokinetics*; D000001:Calcimycin / Q000494:pharmacology; D004347:Drug Interactions; D007425:Intracellular Membranes / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D001639:Bicarbonates; D000804:Angiotensin II; D000001:Calcimycin; D013755:Tetradecanoylphorbol Acetate