Evidence for basolateral membrane Ca2+/H+ exchange in outer medullary collecting duct.
The relationship between Ca2+ and intracellular pH (pHi) was studied in the rabbit collecting duct from the inner stripe of the outer medulla (OMCDi). When bath Ca2+ was lowered [1 mM Ca2+ plus 2 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)] intracellular Ca2+ concentration ([Ca2+]i) decreased by 38.3 +/- 6.2% from 265 +/- 25 to 165 +/- 25 nm (n = 4). Lowering bath Ca2+ produced a biphasic response in pHi, transient acidification (from 6.93 +/- 0.06 to 6.80 +/- 0.06) followed by a return of pHi to levels slightly higher than control (pHi = 6.97 +/- 0.06). The acidification was not blocked by bath amiloride or 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) or lumen N-ethylmaleimide (NEM). However, bath amiloride significantly reduced the initial rate of pHi recovery after acidification (0.70 pH U/min in control vs. 0.39 pH U/min with amiloride). Lanthanum, a Ca2+ pump inhibitor, completely inhibited the acidification. Moreover, lowering bath temperature to 20 degrees C also inhibited the acidification. Acidification was blocked when the bath pH was raised to 8.0, whereas lowering bath Ca2+ markedly acidified cells when bath pH was lowered to 6.0 (delta pHi = 0.28 +/- 0.01). We also measured the transepithelial (Vt) and basolateral (Vbl) membrane voltages. Lowering bath Ca2+ depolarized Vt and Vbl by 12.7 +/- 4.9 and 6.0 +/- 2.0 mV, respectively. In summary, 1) lowering bath Ca2+ caused a biphasic response in pHi of OMCDi cells, and 2) the acidification phase is due to H+ influx associated with the Ca2+ pump.
Department of Medicine, Vanderbilt University, Nashville, Tennessee.
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D000818:Animals; D017920:Antiporters; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D000252:Calcium-Transporting ATPases; D027682:Cation Transport Proteins; D004533:Egtazic Acid / Q000494:pharmacology; D004594:Electrophysiology; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism / Q000502:physiology; D007679:Kidney Medulla; D007685:Kidney Tubules, Collecting / Q000378:metabolism* / Q000502:physiology; D007811:Lanthanum / Q000494:pharmacology; D011817:Rabbits; D013696:Temperature
D017920:Antiporters; D002135:Calcium-Binding Proteins; D027682:Cation Transport Proteins; C027614:calcium-hydrogen antiporters; D004533:Egtazic Acid; D007811:Lanthanum; D000252:Calcium-Transporting ATPases; D002118:Calcium