Positive inotropic action of saponins on isolated atrial and papillary muscles from the guinea‐pig

Abstract

1 The effects of several saponins of animal and plant origin on the contractile activity of atrial and papillary muscles of the guinea-pig were tested. In a concentration of 1 × 10⁻⁵ M, holothurin-A (HL-A), holothurin-B, echinoside-A, echinoside-B and sakuraso-saponin (Saku) exhibited positive inotropic and chronotropic actions whereas desacyl-jego-saponin and ginsenoside-Rd did not. 2 Saponins having a positive inotropic action caused haemolysis of rabbit erythrocytes whereas those without inotropic action did not cause haemolysis. 3 The positive inotropic action of saponins was not affected by practolol, chlorpheniramine, cimetidine and indomethacin. 4 Verapamil (10⁻⁶ M) inhibited the inotropic actions due to HL-A and isoprenaline (10⁻⁸ M) to the same extent but had a small efect on those due to ouabain (10⁻⁷ M). 5 In high K⁺ (30 mM K⁺) medium where the action potential and the contraction were depressed, HL-A, Saku and isoprenaline restored the action potential and the contraction of the ‘slow response’ type whereas ouabain failed to do so. 6 In normal medium HL-A and Saku reduced the resting membrane potential by 15–20 mV. 7 These results suggest that modification of the Ca channel is involved in the positive inotropic action of saponins.