BETAXOLOL, A BETA(1)-ADRENOCEPTOR ANTAGONIST, INHIBITS CA2-INDUCED CONTRACTION IN SKINNED RENAL-ARTERY OF THE DOG()

The effects of betaxolol on Ca2+-induced contractions in saponin-treat ed skinned canine renal arteries were examined. Betaxolol decreased th e pCa (-log[Ca2+] M) 5.8-induced contraction at the same concentration s at which the drug relaxed the high K+-induced contraction in intact smooth muscles. The pCa-tension relation was shifted to the right and downward by betaxolol. Betaxolol inhibited the increase in Ca2+-induce d contraction by calmodulin, and this effect of betaxolol was observed even at the concentration that had no effect when given alone. These results suggest that betaxolol decreases the Ca2+ sensitivity of the c ontractile system in skinned canine renal arteries, presumably by inhi biting calmodulin-mediated contractions.