Betaxolol, αβ₁-Adrenoceptor Antagonist, Inhibits Ca²⁺-Induced Contraction in Skinned Renal Artery of the Dog

Abstract

The effects of betaxolol on Ca²⁺-induced contractions in saponin-treated skinned canine renal arteries were examined. Betaxolol decreased the pCa (-log[Ca²⁺] M) 5.8-induced contraction at the same concentrations 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 Cat+-induced 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 contractile system in skinned canine renal arteries, presumably by inhibiting calmodulinmediated contractions.