Abstract
The contractions of isolated spiral strips from bovine and porcine coronary arteries were induced by potassium depolarization. The preparations were relaxed by verapamil and/or isoproterenol. 1. The non-activated preparation of bovine artery has a basal tone corresponding to 15±1.7% of the maximum of developed tension. 2. The contraction induced by potassium depolarization was largely prevented by 11.3 μg/ml of verapamil. In this preparation, however, 2.8 μg/ml of noradrenaline relaxed the depolarized spiral strip to the same degree as compared with values of the polarized arteries. 3. The depolarized, activated preparation is more relaxed by inhibition of calcium ion influx (verapamil) than by activation of beta-adrenergic receptors (isoproterenol). The relaxing effect takes place in the following order: noradrenaline (51.7%) < isoproterenol (86.1%) < verapamil (100%). 4. The polarized, non-activated preparation is more relaxed by stimulation of beta-adrenergic receptors (isoproterenol) than by inhibition of calcium ion influx (verapamil). The relaxing effect takes place in the following order: verapamil (64.4%) < noradrenaline (85.3%) < isoproterenol (100%). 5. The degree of maximal relaxation after verapamil, noradrenaline, or isoproterenol increases in the polarized preparation with augmented fibre stretch.
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