丙酮酸增加心肌梗死后大鼠心室肌细胞L型钙流的肾上腺素能反应

Pyruvate Increases Adrenergic Reponsiveness of ICa-L in Rat Ventricular Myocytes from Post-infarction Hearts

目的探讨丙酮酸对心肌梗死后大鼠心室肌细胞L型钙流肾上腺素能反应性的影响及其机制。方法取体质量200-250 g雄性SD大鼠,结扎左冠状动脉建立心肌梗死模型,术后6-8周用于实验。采用酶解法获得单个心室肌细胞,应用膜片钳全细胞记录技术记录钙流。结果与对照组（n=4）相比,心肌梗死组（n=13）大鼠心脏/体质量比增加31.4%（P〈0.05）,心室肌细胞膜电容增加41.8%（P〈0.001）;L型钙流密度及其失活动力学未有改变,对异丙肾上腺素（分别为49.4%和11.8%,P〈0.05）及forskolin（分别为46.4%和9.4%,P〈0.001）的反应性则明显下降,用5 mmol/L丙酮酸在体外预处理心肌梗死后大鼠心室肌细胞4-5 h使其反应性恢复,但丙酮酸的这一作用被硫氧还蛋白还原酶抑制剂阻断。结论心肌梗死后大鼠心室肌细胞L型钙流密度未改变,但其对肾上腺素能刺激的反应性明显下降,而丙酮酸通过与硫氧还蛋白系统有关的机制恢复其反应性。

Objective To investigate the effect of pyruvate on the adrenergic responsiveness of L-type calcium current （ICa-L） of ventricular myocytes from post-myocardial infarction （post-MI） rats and its mechanism. Methods The infarction model was established by ligation of left coronary artery using male Sprague-Dawley rats with body weight from 200 gram to 250 gram. Rats with left coronary artery ligation were allowed recovery for 6 to 8 weeks before study. The single ventricular myocytes were obtained by enzymatic method and the whole-cell patch clamp technique was used to record the potassium currents. Results Cardiac hypertrophy was evident by a 31.4% increase in heart weight to body weight ratio（P〈0.05） and a 41.8% increase in whole cell capacitance of isolated left ventricular myocytes （ P 〈 0. 001 ） from post-MI group （ n = 13） compared with the control group（n = 4）. Voltage-clamp experiments revealed that the maximal density of ICa-L measured at 0mV, there is no significant difference in fast and slow inactivation time constant between post-MI and control cells. Relative increase in peak ICa-L density induced by applying 1 gmol/L isoproterenol was significantly greater in the control cells compared with that in the post-MI cells（49.4% vs 11.8%, P〈0.05）. The responsiveness of ICa-L to 1 gmol/L forskolin was similar to that of isoproterenol （46.4% vs 9.4%, P 〈 0. 001 ）. The responsiveness of ICa-L of post-MI cells to isoproterenol and forskolin was restored to the normal level from 4 to 5 hours by pre-treatment with exogeneous pyruvate, however, this increase of responsiveness was blocked by using the inhibitors of thioredoxin reductase. Conclusion The ICa-L density and its responsiveness to adrenergic stimulation are decreased in post-MI cells. Pyruvate mediates the restoration of responsiveness via a mechanism related to the oxidoreductases of thioredoxin and thioredoxin reductase.