Inhibition of Vascular Smooth Muscle Tone by the H+, K+-ATPase Inhibitor SCH 28080

Abstract

Vascular smooth muscle is thought to possess an H+-K+ ATPase that contributes to the regulation of intracellular K+ concentration and pH. We have examined the effect of the H+, K+-ATPase inhibitor SCH 28080 on vascular smooth muscle tone in guinea-pig and human isolated arteries, and on 86Rb+ uptake in cultured guinea-pig aortic smooth muscle cells.SCH 28080 (0.1–300 μM) produced relaxation of isolated guinea-pig aorta, guinea-pig pulmonary artery and human pulmonary artery. Relaxation occurred in tissues pre-contracted with phenylephrine, histamine or the thromboxane mimetic U44069. Relaxation was reversible, and was not affected by tetrodotoxin, indomethacin, nordihydroguiaretic acid (NDGA), 1-aminobenzotriazole (1-ABT), NG-nitro-L-arginine methyl ester (L-NAME), removal of the endothelium or removal of extracellular K+. SCH 28080 had no effect on 86Rb+ uptake in cultured guinea-pig aortic smooth muscle cells.In conclusion, SCH 28080 relaxes vascular smooth muscle at concentrations known to inhibit the H+-K+ ATPase. The persistence of relaxation in a K+-free medium and the failure of SCH 28080 to inhibit 86Rb+ uptake suggest that relaxation may be unrelated to H+, K+-ATPase inhibition, and indicate that this agent may not be considered as a selective H+, K+-ATPase inhibitor in vascular preparations.