Inhibition of ICa,L by DHEA in Aortic Smooth Muscle Cells: Voltage‐dependency, Modulation by GPCR Signaling and Inhibition of Glucose‐6‐phosphate Dehydrogenase

Abstract

Dehydroepiandrosterone (DHEA) is a hormone abundantly released from adrenal cortex as DHEA‐sulfate (DHEA‐S). DHEA‐S is released also in brain. DHEA and epiandrosterone (EPI), a metabolite of DHEA, produces relaxation of high‐K+ induced contraction of aortic smooth muscle (ASM). EPI increases voltage‐dependent inactivation (voltage‐dependent inhibition, VDI) of ICa,L in ventricular myocytes. Whole‐cell ICa,L was recorded as IBa from ASM cells (ASMCs) of A7r5 cell line and enzymatically isolated bovine coronary ASMCs to study mechanism and modulation of DHEA‐induced inhibition of ICa,L. DHEA produced VDI; acceleration of time course of inactivation, increase of inhibition by depolarization of holding potential (HP) and leftward shift of steady state inactivation curve; f∞, 2s‐V, obtained by 2 s conditioning pulse and f∞, HP‐V as a function HP. In addition, DHEA produced voltage‐independent inhibition (VIDI) represented by inhibition of peak amplitude (ICa,L,peak) of ICa,L elicited by pulses from hyperpolarized HPs. Window ICa,L (IWD) supplies Ca2+ in the E‐C coupling of ASM. IWD obtained from I–V of ICa,L,peak and f∞, HP‐V fitted well with recorded IWD and they were strongly inhibited by DHEA. Efficacy of DHEA‐induced VDI was reduced by rightward shift of f∞, 2s‐V curve produced by depletion of cholesterol by MβCD. Blocking of GPCR signaling by intracellular dialysis of GDP‐β‐S also shifted f∞, 2s‐V to the right and it produced decrease of DHEA‐induced inhibition of ICa,L at depolarized HP (VDI). DHEA and EPI are inhibitors of glucose‐phosphate‐dehydrogenase (G6PD), a redox‐related pentose‐phosphate pathway enzyme. 6‐Aminonicotinamide (6‐AN), another inhibitor of G6PD produced VIDI without inducing VDI. DHEA‐S that does not inhibit G6PD induced small but significant VDI at an order higher concentration of DHEA without generating VIDI. GPCR signaling and membrane cholesterol are indirectly involved in the modulation of DHEA‐induced VDI by affecting basal voltage‐dependent inactivation. The occurrence of VIDI by 6‐AN indicates that G6PD inhibition underlies DHEA‐induced VIDI. DHEA‐induced inhibition of IWD by VDI and VIDI contributes for DHEA‐induced relaxation of ASM.Support or Funding InformationNational Heart, Lung, and Blood Institute Grant RO1 HL‐085352 to S. A. Gupte.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.