Effects of procaine on the isolated dog coronary artery

In order to search into the mechanism of the potassium contracture of the dog coronary artery the effects of procaine were studied in the isolated smooth muscle preparation of the dog coronary artery. Procaine is a substance which is known to specifically inhibit the calcium-induced calcium release mechanism. A dose-related relaxation of the potassium contracture was observed with procaine. However, the increase in La3+-resistant 45Ca uptake as measured by the Karaki and Weiss' method (1979) was not inhibited. As reported in a previous paper, caffeine induced a phasic contraction of the fully-depolarized preparation in a calcium-free EGTA containing medium. Procaine produced a dose-related inhibition of this contraction. These findings suggest that the potassium contracture of the dog coronary artery is dependent on the calcium-induced calcium release mechanism. Since the potassium contracture of this preparation can be relaxed by calcium antagonists, it may be inferred that the calcium influx through the voltage-dependent channels may represent the initiation mechanism of the calcium-induced calcium release process.