Na(+)-H+ antiport detected through hydrogen ion currents in rat alveolar epithelial cells and human neutrophils.
Voltage-activated H(+)-selective currents were studied in cultured adult rat alveolar epithelial cells and in human neutrophils using the whole-cell configuration of the patch-clamp technique. The H+ conductance, gH, although highly selective for protons, was modulated by monovalent cations. In Na+ and to a smaller extent in Li+ solutions, H+ currents were depressed substantially and the voltage dependence of activation of the gH shifted to more positive potentials, when compared with the "inert" cation tetramethylammonium (TMA+). The reversal potential of the gH, Vrev, was more positive in Na+ solutions than in inert ion solutions. Amiloride at 100 microM inhibited H+ currents in the presence of all cations studied except Li+ and Na+, in which it increased H+ currents and shifted their voltage-dependence and Vrev to more negative potentials. The more specific Na(+)-H+ exchange inhibitor dimethylamiloride (DMA) at 10 microM similarly reversed most of the suppression of the gH by Na+ and Li+. Neither 500 microM amiloride nor 200 microM DMA added internally via the pipette solution were effective. Distinct inhibition of the gH was observed with 1% [Na+]o, indicating a mechanism with high sensitivity. Finally, the effects of Na+ and their reversal by amiloride were large when the proton gradient was outward (pHo parallel pHi 7 parallel 5.5), smaller when the proton gradient was abolished (pH 7 parallel 7), and absent when the proton gradient was inward (pH 6 parallel 7). We propose that the effects of Na+ and Li+ are due to their transport by the Na(+)-H+ antiporter, which is present in both cell types studied. Electrically silent H+ efflux through the antiporter would increase pHi and possibly decrease local pHo, both of which modulate the gH in a similar manner: reducing the H+ currents at a given potential and shifting their voltage-dependence to more positive potentials. A simple diffusion model suggests that Na(+)-H+ antiport could deplete intracellular protonated buffer to the extent observed. Evidently the Na(+)-H+ antiporter functions in perfused cells, and its operation results in pH changes which can be detected using the gH as a physiological sensor. Thus, the properties of the gH can be exploited to study Na(+)-H+ antiport in single cells under controlled conditions.
Department of Physiology, Rush Presbyterian St. Luke's Medical Center, Chicago, Illinois 60612.
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DeCoursey
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Cherny
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D016623:Ion Pumps / Q000502:physiology*; D017136:Ion Transport; D009504:Neutrophils / Q000378:metabolism*; D017494:Proton Pumps / Q000502:physiology*; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*
D016623:Ion Pumps; D017494:Proton Pumps; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D012964:Sodium