H2O2 regulates recombinant Ca2+ channel α1C subunits but does not mediate their sensitivity to acute hypoxia

Acute hypoxic inhibition of the pore-forming α1C subunit of the L-type Ca2+ channel mediates hypoxic arterial vasodilatation, a physiological response which matches tissue O2 demand and supply in the systemic vasculature. In numerous O2-sensing cell types, reactive O2 species (ROS) have been proposed as mediators linking lowered O2 levels with the appropriate cellular response. In this study, we examined the roles of H2O2 and NADPH oxidase as mediators of hypoxic inhibition of recombinant α1C subunits. Human cardiac L-type Ca2+ channel α1C subunits were stably expressed in HEK 293 cells. Ca2+ currents were recorded using the whole-cell configuration of the patch-clamp technique. Bath application of 100μM H2O2 significantly enhanced depolarisation-evoked Ca2+ currents in a voltage-dependent manner, while dialysis with 1000Uml-1 catalase reduced these currents. In the presence of catalase, hypoxic inhibition of Ca2+ currents was not significantly different compared to non-dialysed controls. The NADPH oxidase inhibitors diphenylene iodonium (10μM) and phenylarsine oxide (5μM) were without effect on either basal Ca2+ currents or responses to hypoxia. Thus, endogenous production of H2O2 regulates the α1C subunit. However, neither suppression of H 2O2 levels nor inhibition of NADPH oxidase is involved in O2-dependent regulation of the Ca2+ channel. © 2004 Elsevier Inc. All rights reserved.