Furuya H, Jacobson H R, Breyer M D
Department of Medicine, Vanderbilt University, Nashville, Tennessee.
Am J Physiol. 1993 Jan;264(1 Pt 2):F88-93. doi: 10.1152/ajprenal.1993.264.1.F88.
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.
研究了外髓质内层兔集合管（OMCDi）中钙离子（Ca2+）与细胞内pH值（pHi）之间的关系。当浴液中Ca2+浓度降低时[1 mM Ca2+加2 mM乙二醇双（β-氨基乙醚）-N,N,N',N'-四乙酸（EGTA）]，细胞内Ca2+浓度（[Ca2+]i）从265±25 nM降至165±25 nM，降低了38.3±6.2%（n = 4）。降低浴液中Ca2+浓度会使pHi产生双相反应，先是短暂酸化（从6.93±0.06降至6.80±0.06），随后pHi恢复到略高于对照的水平（pHi = 6.97±0.06）。酸化过程不受浴液中氨氯吡咪、4,4'-二异硫氰基芪-2,2'-二磺酸（DIDS）或管腔N-乙基马来酰亚胺（NEM）的阻断。然而，浴液中的氨氯吡咪显著降低了酸化后pHi恢复的初始速率（对照为0.70 pH单位/分钟，氨氯吡咪处理后为0.39 pH单位/分钟）。镧系元素，一种Ca2+泵抑制剂，完全抑制了酸化。此外，将浴液温度降至20℃也抑制了酸化。当浴液pH值升至8.0时，酸化被阻断，而当浴液pH值降至6.0时，降低浴液中Ca2+浓度会使细胞明显酸化（ΔpHi = 0.28±0.01）。我们还测量了跨上皮（Vt）和基底外侧（Vbl）膜电压。降低浴液中Ca2+浓度分别使Vt和Vbl去极化12.7±4.9 mV和6.0±2.0 mV。总之，1）降低浴液中Ca2+浓度会使OMCDi细胞的pHi产生双相反应，2）酸化阶段是由于与Ca2+泵相关的H+内流所致。
