Pharmaceutical Laboratory I, Yokohama Research Center, Mitsubishi Chemical Corporation, 1000 Kamoshida-cho, Aoba-ku, Yokohama 227, Japan
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 Ca2+-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 calmodulin- mediated contractions.
Betaxolol, Ca2+ sensitivity, Skinned smooth muscle
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