CGMP-KINASE MEDIATES CGMP-INDUCED AND CAMP-INDUCED CA2+ DESENSITIZATION OF SKINNED RAT ARTERY

(Rp)-8-Bromo-guanosine 3',5'-cyclic monophosphorothioate (Rp-8-Br-cGMP S) inhibited competitively both isozymes of type I alpha and I beta cG MP-dependent protein kinase (cGMP-kinase) purified from porcine aorta with apparent K-i values (mu M) of 3.7 for I alpha and 1.8 for I beta. The compound also inhibited bovine heart type II cAMP-dependent prote in kinase (cAMP-kinase), but with a K-i of 25 mu M. Thus, it is a sele ctive inhibitor of cGMP-kinase. In alpha-toxin-skinned smooth muscle p reparations from rat mesenteric artery, 8-Br-cGMP (10(-7) M) and 8-Br- cAMP (10(-6) M) produced a rightward shift of the concentration-contra ction curves for Ca2+, denoting a decrease in Ca2+ sensitivity of the contractile elements. The shift by 8-Br-cAMP as well as by 8-Br-cGMP w as completely reversed by Rp-8-Br-cGMPS, while a selective inhibitor o f activation of cAMP-kinase, (Rp)-adenosine-3',5'-cyclic monophosphoro thioate (Rp-cAMPS), was without effects on the shift produced by these two compounds. These findings indicate the pivotal role that the acti vation of cGMP-kinase plays in the production of a decrease in Ca2+ se nsitivity of contractile elements. (C) 1997 Elsevier Science B.V.