Pharmacological Inhibition of Glucose‐6‐phosphate Dehydrogenase Produces Inhibition of L‐type Calcium Channel Current in Arterial Smooth Muscle Cells

Abstract

Glucose‐6‐phosphate dehydrogenase (G6PD) is the first enzyme in pentose phosphate pathway (PPP). G6PD is involved in cellular redox regulation by reducing NADP+ to NADPH, a primary cellular reducing agent, and PPP produces ribose 5‐phosphate, a substrate necessary for nucleotide synthesis. We used two inhibitors of G6PD, 6‐aminonicotinamide (6‐AN) and dehydroepiandrosterone (DHEA), to clarify involvement of G6PD in the regulation of L‐type Ca2+ channel current (ICa,L) in arterial smooth muscle cells (ASMCs). 6‐AN is converted to 6‐ANADP in the cell to competitively inhibit NADP+ binding to G6PD. DHEA is an adrenal steroid hormone with the highest serum concentration among steroid hormones with its sulfate ester DHEAS. DHEA inhibits G6PD in a non‐competitive manner. The potency of DHEAS to inhibit G6PD is about 1/100 of DHEA. DHEA induced relaxation of high K+‐induced contraction in arterial strips excised from carotid artery and aorta of rat in a dose‐dependent manner. In contrast, DHEAS did not produce the relaxation. In previous meetings we reported that DHEA inhibits ICa,L in voltage‐dependent and ‐independent mechanisms in ASMCs. 6‐AN produced voltage‐independent inhibition of ICa,L recorded with 10 mM Ba2+ as the charge carrier in A7r5 ASMCs. When constant depolarization step was repetitively applied from hyperpolarized HP, 6‐AN (3 mM) gradually induced inhibition of ICa,L decreasing the peak amplitude of ICa,L (ICa,L, peak) by 25% in 5 min and 45% in 10 min. The inhibition was not reversible by washout of 6‐AN. This was in contrast to DHEA‐induced inhibition of ICa,L which exhibits rapid onset and rapid recovery by washout. 6‐AN little affected the time course of inactivation of ICa,L during depolarization steps, while DHEA markedly accelerated the time course. When I‐V relationship was obtained with 5 min interval before and during application of 6‐AN, ICa,L did not significantly change in control, but decreased in 5 min in the presence of 6‐AN and the inhibition was increased by another 5 min application of 6‐AN. In the presence of 6‐AN, 0.1 mM DHEA rapidly decreased ICa,L,peak and markedly accelerated the time course of inactivation in a reversible manner. Inhibition of G6PD by 6‐AN and DHEA could inhibit ICa,L,peak by thiol‐oxidation of CaV1.2 channel proteins via decrease of NADPH. DHEA additionally augmented voltage‐dependent inactivation of ICa,L in a mode of open channel block produced by Ca2+ channel blockers.Support or Funding InformationNational Heart, Lung, and Blood Institute Grant RO1‐HL‐085352 and ROI‐HL‐132574 to S.A.G.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.