ABSTRACT
Effect of strophanthidin (Str) on intracellular calcium concentration ([Ca2+]i) was investigated on isolated ventricular myocytes of guinea pig. Single ventricular myocytes were obtained by enzymatic dissociation technique. Fluorescent signal of [Ca2+]i was detected with confocal microscopy after incubation of cardiomycytes in Tyrode's solution with Fluo3-AM. The result showed that Str increased [Ca2+]i in a concentration-dependent manner. The ventricular myocytes began to round-up into a contracture state once the peak level of [Ca2+]i was achieved in the presence of Str (10 μmol·L-1), but remained no change in the presence of Str (1 and 100 nmol·L-1). Tetrodotoxin (TTX), nisodipine, and high concentration of extracellular Ca2+ changed the response of cardiomycytes to Str (1 and 100 nmol·L-1), but had no obvious effects on the action of Str (10 μmol·L-1). The elevation of [Ca2+]i caused by Str at all of the detected concentrations was partially antagonized by rynodine (10 μmol·L-1) or the removal of Ca2+ from Tyrode's solution. In Na+, K+-free Tyrode's solution, the response of cardiomycytes in [Ca2+]i elevation to Str (10 μmol·L-1) was attenuated, while remained no change to Str (1 and 100 nmol·L-1). TTX, nisodipine, and high concentration of extracellular Ca2+ changed the response of cardiomycytes to Str at all of the detected concentrations in Na+, K+-free Tyrode's solution. The study suggests that the elevation of [Ca2+]i by Str at the low (nomomolar) concentrations is partially mediated by the extracellular calcium influx through Ca2+ channel or a "slip mode conductance" of TTX sensitive Na+ channel. While the effect of Str at high (micromolar) concentrations was mainly due to the inhibition of Na+, K+-ATPase. Directly triggering the release of intracellular Ca2+ from sarcoplasmic reticulum (SR) by Str may be also involved in the mechanism of [Ca2+]i elevation.
ABSTRACT
AIM To study the effects of strophanthidin (Str) on cardiac function and Na +,K +-ATPase activity in isolated guinea pig heart failure model. METHODS Langendorff isolated heart failure models made by perfusing heart with K-H solution containing sodium pentobarbital. Eight-channel physiological recording instrument was used to determine cardiac function. Colorimetry method was used to determine cardiac sarcolemmal Na +,K +-ATPase activity. RESULTS Str increased the heart rate, left ventricular systolic pressure and the maximum rise or decline rate of left ventricular pressure in a concentration-dependent manner at 1?10 -9～1?10 -7 mol?L -1. But Str caused first a rise, then a reduction of contractility and arrhythmia accompanied by inhibition of Na +,K +-ATPase when the concentration of Str was higher than 1?10 -6 mol?L -1. Str had no obvious effect on Na +,K +-ATPase activity at 1?10 -7 mol?L -1, but increased cardiac activity at 1?10 -10～1?10 -8 mol?L -1. CONCLUSION The inotropic effect and heart toxicity of Str at higher concentration is due to inhibition of Na +,K +-ATPase, but the inotropic effect of Str at lower concentration is not the result of inhibition of Na +,K +-ATPase activity.