Vornanen M, Shepherd N, Isenberg G
Department of Physiology, University of Cologne, Germany.
Am J Physiol. 1994 Aug;267(2 Pt 1):C623-32. doi: 10.1152/ajpcell.1994.267.2.C623.
Contractile tension in response to 200-ms voltage-clamp pulses was measured in isolated guinea pig ventricular cells conditioned to constant Ca load. At 23 degrees C, the tension-voltage relation was bell shaped, decaying from a maximum at +20 mV to zero at +100 mV, but at 35 degrees C it was sigmoidal, with similar twitch tensions at +20 and +100 mV. Tension at 35 degrees C and +100 mV was reduced by ryanodine or caffeine and abolished by removal of Ca just before the test pulse. At 35 degrees C and +100 mV, twitch tension increased markedly as the Na concentration in the patch pipette ([Na]p) was varied between 0 and 20 mM. Cd (300 microM) blocked tension at all potentials at 23 degrees C, but tension remained in the presence of Cd at 35 degrees C (29% of control at +2 mV and 100% of control at +100 mV). Cd-resistant tension began to relax during the clamp pulse at all potentials (80 +/- 10 ms at +2 mV and 140 +/- 12 ms at +100 mV). Ni (3.6 mM) both reduced and slowed tension transients at all potentials. The results suggest that fast contractions due to sarcoplasmic reticulum Ca release can be triggered by Ca influx through either Ca current (ICa) or Na/Ca exchange and that those triggered through exchange are much more temperature sensitive than those triggered by ICa.
在条件设定为恒定钙负荷的豚鼠离体心室细胞中，测量了对200毫秒电压钳脉冲的收缩张力。在23摄氏度时，张力-电压关系呈钟形，从+20毫伏时的最大值衰减至+100毫伏时的零值，但在35摄氏度时呈S形，在+20毫伏和+100毫伏时具有相似的单收缩张力。35摄氏度和+100毫伏时的张力可被兰尼碱或咖啡因降低，并在测试脉冲前去除钙时消除。在35摄氏度和+100毫伏时，当膜片吸管中的钠浓度（[Na]p）在0至20毫摩尔之间变化时，单收缩张力显著增加。镉（300微摩尔）在23摄氏度时阻断了所有电位下的张力，但在35摄氏度时存在镉的情况下仍有张力（在+2毫伏时为对照的29%，在+100毫伏时为对照的100%）。在所有电位下，抗镉张力在钳制脉冲期间开始松弛（在+2毫伏时为80±10毫秒，在+100毫伏时为140±12毫秒）。镍（3.6毫摩尔）在所有电位下均降低并减缓了张力瞬变。结果表明，肌浆网钙释放引起的快速收缩可由通过钙电流（ICa）或钠/钙交换的钙内流触发，并且通过交换触发比由ICa触发的收缩对温度更敏感。
