EFFECTS OF DILTIAZEM AND LANTHANUM ION ON THE POTASSIUM CONTRACTURE OF ISOLATED GUINEA PIG SMOOTH MUSCLE

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Abstract
Effects of diltiazem [a coronary vasodilator] on K-induced contracture of the smooth muscle were examined in the isolated tenia coli and stomach strip of the guinea pig. Results were compared with those of La3+. K-contracture was evoked by isotonic K-Krebs solution. La3+ inhibited K-contracture of the tenia coli and effects on the phasic response were more remarkable than on the tonic response. After the removal of La3+, the phasic response almost regained its normal magnitude; the tonic response was significantly augmented. Diltiazem inhibited the tonic response more markedly than the phasic response in tenia coli and stomach strip. Inhibition of the phasic response was elicited in association with decrease in the frequency of spike discharge during rapid membrane depolarization. The effects of diltiazem were completely reversed after washing out the compound. Although both La3+ and diltiazem inhibit the transmembrane influx of Ca2+, additional mechanisms may differ.