Penna M, Valenzuela M I
Arzneimittelforschung. 1977;27(3):583-9.
In isolated cat heart papillary muscle electrically driven at the basic rate of 30 per min the effect of change in temperature (37 degrees C vs. 30 degrees C) and caffeine upon post-extrasystolic potentiation (PEP) phenomenon was studied. At 30 degrees C the basic tension developed by the regular contraction increased an average of (s +/- sm) 23 +/- 5.2% as compared to 37 degrees C. Furthermore at 30 degrees C, the curve relating the magnitude of PEP to the interval (msec) between regular and premature stimulus was significantly shifted upwards and to the right as compared to the curve obtained at 37 degrees C. The time persistence effect of PEP or at 30 degrees C. In fact, up to 5 min the corrected curve relating percentage increase of the first potentiated contraction with predetermined intervening rest period (pause) was significantly shifted upwards at the lower temperature. Caffeine (2.7 and 5.4 mM/l at 37 degrees C) produced a significant increase (s +/- sm) + 51.5 +/- 6.8% of the basic tension developed by the regular contractions as compared to the control period in the same muscles. However, caffeine decreased significantly both the relative magnitude (%) and the time persistence (corrected values) of PEP appearing on the first contraction after a predetermined interveinin pause. In control experiments in the same muscles caffeine decreased the tension developed by the first contraction following any equivalent pause during rhythmic stimulation. This relative decrease in tension of the first contraction reached a greater significance as the pause was lengthened to the limits of the rested state contraction (5 min). The results are discussed regarding the excitation-contraction coupling and calcium inactivation as the main mechanisms for positive inotropic effect during PEP. The effect of lowering the temperature could be related to the lengthening of the active state, slowing of Ca++ inactivation mechanism and/or greater stiffness of the serial elastic element. The effect of caffeine is probably related to an increase of the intracellular Ca displacement to the contractile site.
在以每分钟30次的基础频率进行电驱动的离体猫心乳头肌中，研究了温度变化（37℃与30℃）和咖啡因对期外收缩后增强（PEP）现象的影响。在30℃时，与37℃相比，由规则收缩产生的基础张力平均增加了（s±sm）23±5.2%。此外，在30℃时，与37℃时获得的曲线相比，PEP幅度与规则刺激和过早刺激之间的间隔（毫秒）的关系曲线明显向上和向右移动。PEP的时间持续效应在30℃时也有所不同。实际上，在较低温度下，长达5分钟的将第一次增强收缩的百分比增加与预定的中间休息期（暂停）相关的校正曲线明显向上移动。咖啡因（37℃时为2.7和5.4 mM/l）与同一肌肉的对照期相比，使规则收缩产生的基础张力显著增加（s±sm）+51.5±6.8%。然而，咖啡因显著降低了在预定的中间暂停后第一次收缩时出现的PEP的相对幅度（%）和时间持续性（校正值）。在同一肌肉的对照实验中，咖啡因降低了节律性刺激期间任何等效暂停后第一次收缩产生的张力。随着暂停延长至静息状态收缩的极限（5分钟），第一次收缩张力的这种相对降低变得更加显著。讨论了关于兴奋 - 收缩偶联和钙失活作为PEP期间正性肌力作用的主要机制的结果。降低温度的影响可能与活性状态的延长、Ca++失活机制的减慢和/或串联弹性元件的更大刚度有关。咖啡因的作用可能与细胞内Ca向收缩部位的位移增加有关。
