INHIBITION OF THE PHARMACOLOGICAL ACTIONS OF GLYCERYL TRINITRATE AFTER THE ELECTROPORETIC DELIVERY OF A GLUTATHIONE-S-TRANSFERASE INHIBITOR

It is generally accepted that the biotransformation of organic nitrate s to an activator of soluble guanylyl cyclase (presumably NO) is a pre requisite for their vasodilator actions. The glutathione S-transferase s (GSTs) mediate glyceryl trinitrate (GTN) biotransformation, but whet her this results in guanylyl cyclase activation and relaxation of vasc ular smooth muscle is equivocal. We used electroporation of adherent c ultured cells to deliver the membrane-impermeable GST inhibitor basile n blue (BE) into porcine kidney epithelial cells. This resulted in sig nificant inhibition of GTN biotransformation because of a reduction in the formation of glyceryl-1,2-dinitrate, but not glyceryl-1,3-dinitra te. In the 105,000 x g supernatant fraction of porcine kidney epitheli al cells, BE significantly inhibited the formation of both GTN metabol ites. Electroporation of porcine kidney epithelial cells with BE also inhibited GTN-induced cyclic GMP accumulation. This was caused in part by inhibition of soluble guanylyl cyclase by BE. To differentiate BE- mediated inhibition of the bioactivation of GTN from its inhibitory ef fect on guanylyl cyclase, inhibition of cyclic GMP accumulation induce d by GTN and that induced by the spontaneous NO-releasing compound, t- butyl-S-nitrosothiol were compared. Maximum inhibition of cyclic GMP a ccumulation by BE was 80% and 40% with GTN and t-butyl-S-nitrosothiol as the stimulating compounds, respectively. These data suggest that GS Ts mediate the biotransformation of GTN to an activator of guanylyl cy clase and support the contention that vascular GSTs participate in med iating the relaxant effects of organic nitrates.