L‐type Ca2+ channel current from on‐cell patch is augmented by H2O2 in rat aortic smooth muscle–derived A7r5 cells

Abstract

L‐type Ca2+ channels are exposed to H2O2 generated within the cells and adjacent cells such as immune cells. Although the effect of H2O2 on ICa,L has long been studied, whether it augments or inhibits ICa,L has not yet been settled. We hypothesized that extracellular and intracellular H2O2 differently modulates ICa,L. Here, we adopted two configurations of patch clamp technique to separately study these modulations in A7r5 cells, a smooth muscle cell line derived from embryonic rat aorta. Whole cell ICa,L recorded with 10 mM Ba2+ as a charge carrier was slightly inhibited with an acceleration of its decay time course by 0.1‐mM H2O2. On‐cell recording enabled us to study the effect of H2O2 without possible complication of direct oxidation of CaV1.2 by external H2O2. Single and multichannel ICa,L were recorded in the presence of 90 mM Ba2+ and Bay K 8644 repetitively applying 500 ms depolarization steps to ‐10 and 0 mV. The mean currents from these currents were significantly increased by 0.1‐mM H2O2 from 0.85 pA to 1.05 pA associated with slow inactivation: ICa,L at 500 ms, 0.56 pA in control and 0.74 pA in the presence of H2O2. Since extracellular H2O2 was not accessible to the patch membrane, these changes reflect intracellular actions of H2O2. In conclusion, ICa,L is augmented by H2O2 via intracellular signaling mechanism in A7r5 cells. Supported by National Heart, Lung, and Blood Institute Grant RO1‐HL‐085352.