THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Copyright C iss by The American Society for Pharmacology and Experimental Therapeutics Guanine Nucleotide Binding Proteins May Modulate Gating of Calcium Channels in Vascular Smooth Muscle. II. Stu

Our previous studies with fluoride have indicated that G-proteins may mediate the gating of Ca4 channels in vascular smooth muscle (VSM). We now present further studies on the relation-ship between G-proteins and Ca4 channels in VSM using guan-osine-5’-(’y-thio)triphosphate (GTP-yS), a hydrolysis-resistant an-alog of GTP. Rat tail artery helical strips pretreated with GTP-YS in a cytosol-like solution contracted in a Ca-dependent manner in the absence of a depolarizing concentration of K, hormones or any other Ca agonists. Contraction was dependent on the concentrations of appl#{234}edGTP’YS. The ality of strips pretreated with GTP”YS to contract in response to Ca was not reversed by repeated washing. Incubation with 1 mM GTP applied extra-cellularly did not induce tension development. Treatment with a subthreshold concentration of GTP’YS shifted the K concentra-tion-related tension curve to the left but did not alter the maxi