Takagi S, Kihara Y, Toyoda F, Morita T, Sasayama S, Mitsuiye T
Departments of Physiology and Cardiovascular Medicine, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
Am J Physiol. 1999 Apr;276(4):R923-8. doi: 10.1152/ajpregu.1999.276.4.R923.
Guinea pigs were exposed to 5 degrees C for 3 wk, and the contractions of myocardial papillary muscle were compared with preparations dissected from control animals kept at approximately 25 degrees C. Developed tension of the papillary muscle per cross-sectional area was significantly (t-test, P < 0.05) decreased after cold exposure (19,200 +/- 8,160 vs. 3,020 +/- 2,890 dyne/cm2; 1 Hz). Time to peak tension was significantly faster in cold-exposed guinea pigs (126.4 +/- 11.1 ms; 1 Hz) than in controls (162.7 +/- 8. 7 ms). The magnitude of the developed tension after application of ryanodine (2 mM) to muscles from cold-exposed animals was decreased to 37.5 +/- 8.3% of control at 1 Hz, whereas in muscles from control animals, tension was decreased to 82.4 +/- 7.7%. The ryanodine-sensitive component of contraction was not significantly changed in control guinea pigs at frequencies >0.5 Hz, whereas in muscles from cold-acclimated guinea pigs, there was a "positive staircase." These results suggested that reversal of the Na+/Ca2+ exchanger is predominantly involved in the positive staircase in control guinea pigs, whereas rate-dependent increases in the Ca2+ store in the sarcoplasmic reticulum may be involved in the staircase after cold acclimation.
将豚鼠置于5摄氏度环境中3周，然后将其心肌乳头肌的收缩情况与从饲养在约25摄氏度环境中的对照动物身上分离出的标本进行比较。冷暴露后，每横截面积的乳头肌发育张力显著降低（t检验，P<0.05）（19200±8160对3020±2890达因/平方厘米；1赫兹）。冷暴露的豚鼠达到峰值张力的时间（126.4±11.1毫秒；1赫兹）比对照组（162.7±8.7毫秒）显著加快。对冷暴露动物的肌肉施加ryanodine（2毫摩尔）后，1赫兹时发育张力的幅度降至对照的37.5±8.3%，而对照动物肌肉的张力降至82.4±7.7%。在频率>0.5赫兹时，对照豚鼠收缩的ryanodine敏感成分没有显著变化，而在冷适应豚鼠的肌肉中，出现了“正阶梯现象”。这些结果表明，在对照豚鼠中，Na+/Ca2+交换体的逆转主要参与正阶梯现象，而冷适应后，肌浆网中Ca2+储存的速率依赖性增加可能参与正阶梯现象。
