Spontaneous autocrine release of protons activates ASIC‐mediated currents in HEK293 cells

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Abstract
When examining HEK293 cells by whole‐cell patch‐clamp electrophysiology we found spontaneous currents, present in almost all cells. These currents were carried by Na+ ions, were inhibited by amiloride and by cells exposure to acidic (pH 6.3) extracellular solutions. These properties (ion carrier, amiloride‐sensitivity, and inactivation by constant lowering of extracellular pH) were similar to the properties of proton‐activated currents measured from the same cells. Spontaneous currents required intracellular ATP, were completely inhibited by intracellular Ca2+ buffering with BAPTA and were suppressed by intracellular administration of vesicular H+ATPase inhibitor bafilomycin. ATP‐induced Ca2+ influx through P2X receptors in HEK293 cells stably transfected with P2X2, P2X2/3 or P2X4 purinoreceptor subunits transiently potentiated amplitude and frequency of spontaneous currents; this effect was antagonized by bafilomycin. We concluded that spontaneous currents represent activation of acid‐sensitive ion channels (ASICs) by autocrine vesicular release of protons from HEK cells. © 2007 Wiley‐Liss, Inc. J. Cell. Physiol. 212: 473–480, 2007.