Contrasting effects of betaxolol and propranolol on Ca(2+)-activated contractions in skinned fibers from canine coronary arteries and ventricular muscles.
The effects of some beta-adrenoceptor antagonists (atenolol, betaxolol, bunitrolol, labetalol, pindolol, and propranolol) on Ca2+ (pCa 5.8)-activated tension development in chemically skinned fibers from canine coronary artery and right ventricular trabeculae were studied. In skinned coronary arteries, Ca(2+)-activated tension development was decreased by betaxolol and propranolol at concentration of more than 10(-5) and 10(-4) M, respectively. The pCa-tension relationships were shifted to the right and down by betaxolol. In contrast, in skinned cardiac muscle Ca(2+)-activated tension development was increased by betaxolol and propranolol at the same range of concentrations as in coronary arteries, with no change in maximum tension. The pCa-tension relation was shifted to the left by betaxolol. Other beta-adrenoceptor antagonists (atenolol, bunitrolol, labetalol, and pindolol) had no effect on Ca(2+)-induced contraction in either muscle type. These results indicate that among beta-adrenoceptor antagonists, only betaxolol and propranolol can directly modulate the Ca2+ sensitivity of myofilaments and have opposite effects on the contractile system in canine cardiac and vascular smooth muscle.
Kitada
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Pharmaceutical Laboratory I, Yokohama Research Center, Mitsubishi Chemical Corporation, Japan.
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D015784:Betaxolol / Q000494:pharmacology*; D002118:Calcium / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D003285:Contractile Proteins / Q000494:pharmacology*; D003331:Coronary Vessels / Q000187:drug effects; D004285:Dogs; D005260:Female; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D011433:Propranolol / Q000494:pharmacology*; D014661:Vasoconstriction / Q000187:drug effects*
D000319:Adrenergic beta-Antagonists; D003285:Contractile Proteins; D011433:Propranolol; D015784:Betaxolol; D002118:Calcium