DHEA‐induced Voltage‐dependent Inhibition of ICa,L Is Augmented by Cholesterol Depletion and Down‐regulated by GPCR Blockade in Aortic Smooth Muscle Cells

Abstract

Dehydroepiandrosterone (DHEA) is a steroid hormone synthesized from cholesterol and abundantly secreted as DHEA sulfate from the adrenal gland. DHEA produces relaxation of systemic and pulmonary arterial smooth muscles (ASM) and epiandrosterone, a metabolite of DHEA, causes voltage‐dependent inhibition (VDI) of ICa,L in ventricular myocytes. Here, we characterized DHEA‐induced VDI of ICa,L recorded with Ba2+ as a charge carrier by whole cell clamp and studied underlying mechanism and modulation by signal transduction in ASM cells (ASMCs) from bovine coronary artery and A7r5 cells from rat aorta. DHEA decreased peak amplitude of ICa,L rapidly, reversibly and dose‐dependently and accelerated time course of current decay decreasing the ratio of current amplitude at 500 ms (r500) to peak amplitude and shifted steady‐state inactivation curve (f∞‐V) to the left. DHEA‐induced inhibition of ICa,L became prominent by depolarization of holding potential; e.g. at −30 mV, the inhibition was 29% at 10 μM and 89% at 100 μM. Blockade of GPCR by dialysis of GDP βS shifted both f∞‐V and I–V relationships to the depolarizing direction, and decreased 10 μM‐DHEA‐induced VDI obtained at HP of −40 mV by 40%. Depletion of membrane cholesterol by methyl‐b‐cyclodextrin increased r500 and shifted f∞‐V to the right. Conversely, loading PEG‐cholesterol, a non‐ionic amphiphile, to the membrane decreased r500 and shifted f∞‐V to the left. In the cholesterol‐depleted cells, DHEA produced more potent decrease of r500 and larger negative shift of f∞‐V than in control. Therefore, DHEA‐induced VDI of ICa,L in ASMCs is due, at least partly, to cholesterol‐like action of DHEA on CaV1.2 in the membrane lipid bilayer. GPCR‐mediated signaling regulates voltage‐dependence of basal ICa,L and indirectly augments DHEA‐induced VDI of ICa,L in ASMCs.