毒毛旋花子苷元对豚鼠心室肌细胞内钙浓度的影响

观察毒毛旋花子苷元(strophanthidin, Str)对分离豚鼠心室肌细胞内游离钙浓度(［Ca²⁺］_i)的影响。酶解分离豚鼠心室肌细胞, 用Fluo 3-AM负载, 激光共聚焦显微镜法测定单个豚鼠心室肌细胞［Ca²⁺］_i的荧光密度。Str可浓度依赖性地升高［Ca²⁺］_i, Str (10 μmol·L^-1)在［Ca²⁺］_i升高达峰值时, 可使细胞挛缩, 而Str (1和10 nmol·L^-1)对细胞形态无影响。TTX、 尼索地平或升高细胞外钙可影响Str (1和100 nmol·L^-1)对［Ca²⁺］_i的升高作用,而对Str (10 μmol·L^-1)无明显影响。在外液中加入ryanodine或去除细胞外钙, 则3个检测浓度的Str升高［Ca²⁺］_i作用均被明显抑制。在无K⁺、 无Na⁺液中, 10 μmol·L^-1 Str升高［Ca²⁺］_i的作用减弱, 而Str (1和100 nmol·L^-1)升高［Ca²⁺］_i的作用无明显影响。加入TTX、 尼索地平或增加细胞外的钙离子浓度, 则3个检测浓度Str的作用均受到影响。提示低浓度Str对［Ca²⁺］_i的升高作用与抑制Na⁺、K⁺-ATP酶活性无关, 而与促进L-型钙通道和TTX敏感性钠通道的“slip-mode”钙电导有关; 高浓度Str升高［Ca²⁺］_i的作用则是抑制Na⁺、K⁺-ATP酶的结果。此外, Str对［Ca²⁺］_i的升高作用还与直接作用于ryanodine受体促进内钙释放有关。

Effects of strophanthidin on intracellular calcium concentration in ventricular myocytes of guinea pig

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 micromol 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 micromol L(-1)). The elevation of Ca2+]i caused by Str at all of the detected concentrations was partially antagonized by rynodine (10 micromol 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 micromol 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.