Abstract
The effects of betaxolol on isolated rat arteries and the modes of action were investigated. Betaxolol (10-5 - 10-3M) relaxed the 80 mM K+-induced contraction of aortic strips concentration-dependently. The 50% inhibitory concentration of betaxolol in the K+-induced contraction was 3 times higher than that of papaverine and about 3 times lower than that of bunitrolol. The relaxations by betaxolol were also demonstrated in renal, mesenteric and femoral arteries. Betaxolol (3 × 10-6M - 10-4M) produced rightward parallel shifts of the concentration-response curves for Ca 2+ in the K+-depolarized aortic strips. On the other hand, betaxolol produced downward shifts as well as rightward shifts of the concentration-response curves for norepinephrine, 5-HT and angiotensin II. In K+-depolarized aortic strips, the cytosolic Ca2+ concentration measured with a fluorescent indicator, fura-2, was decreased by betaxolol (10-4M) almost concomitantly with the loss of tention. An elevation of external Ca2+ from 2.5 mM to 10 mM restored both the cytosolic Ca2+ concentration and tention. The relaxations of arteries induced by betaxolol were not influenced by glybenclamide, methylene blue, indomethacin or removal of the endothelium. These results suggest that betaxolol possesses a direct vasodilating action, and the action may be due to the inhibition of Ca2+ influx across the cell membrane.
