Quantitization of Ca spike frequency in a single sucrose gap and mechanical relaxation induced by Ca antagonists, isoproterenol and papaverine.

The suppression of the Ca spike frequency generated spontaneously in the guinea-pig taenia coli was quantitatively investigated using the single sucrose gap method in an attempt to correlate frequency with the relaxation induced by Ca antagonists, isoproterenol and papaverine. The intrinsic activity (a) of depleted Ca that gave the maximal response in the dose-spike frequency curve (DSfC) or dose-tension curve (DTC) was taken as unity. Verapamil and MnCl2: a of both the DSfC and DTC were 1.0. Papaverine: a of the DSfC was 0.5 in contrast to 1.0 in the case of the DTC, and the affinity of the DSfC was somewhat less than that of the DTC. Isoproterenol: a and affinity of the DSfC were considerably less than in the case of the DTC. These results indicate that (1) relaxation induced by the Ca antagonists we used clearly corresponded to the suppression of the Ca influx carrying the action potential, (2) the relaxation induced by isoproterenol was not due to direct suppression of Ca influx, and (3) papaverine and depleted Ca influenced Ca both directly and indirectly.U