MacIntosh B R, Posner P, Lobo J, Harms R
Department of Medical Physiology, University of Calgary, Alta., Canada.
Can J Physiol Pharmacol. 1992 Feb;70(2):275-82. doi: 10.1139/y92-034.
Caffeine has been reported to have a positive and (or) a negative inotropic effect on cardiac muscle. In this study, the force-frequency and postrest characteristics of rat atrium were studied in the presence of caffeine (1.0-10 mM) to see if the interval between beats affected the response of cardiac muscle to caffeine. When stimulation frequency was 0.5 or 2.0 Hz, there was a positive followed by a negative inotropic response with 1, 5, or 10 mM caffeine. Incomplete relaxation occurred under these circumstances, giving rise to contracture. At low frequency of stimulation (0.1 Hz) caffeine had only a negative inotropic effect, and this effect was greater with 1 mM caffeine than with 5 mM caffeine. In the absence of caffeine, when stimulation at 0.5 or 3 Hz was interrupted, a pause of 2-20 s resulted in potentiation. When caffeine was present (2.0 mM), postrest potentiation was severely attenuated, but the steady-state contraction amplitude within the range 0.5-3.0 Hz was not different. These results are consistent with the hypothesis that caffeine induces a leak of Ca2+ from the sarcoplasmic reticulum, and this Ca2+ is extruded from the cell, possibly by Na+/Ca2+ exchange. Sarcoplasmic reticular uptake of Ca2+ and the translocation to release sites appear not to be affected by caffeine within 1-5 mM concentrations.
据报道，咖啡因对心肌具有正性和（或）负性肌力作用。在本研究中，研究了在咖啡因（1.0 - 10 mM）存在的情况下大鼠心房的力 - 频率和静息后特征，以观察心跳间隔是否会影响心肌对咖啡因的反应。当刺激频率为0.5或2.0 Hz时，1、5或10 mM咖啡因会产生先正性后负性的肌力反应。在这些情况下会出现不完全舒张，导致挛缩。在低频刺激（0.1 Hz）时，咖啡因仅具有负性肌力作用，且1 mM咖啡因的这种作用比5 mM咖啡因更强。在无咖啡因的情况下，当0.5或3 Hz的刺激中断时，2 - 20秒的停顿会导致增强作用。当存在咖啡因（2.0 mM）时，静息后增强作用会严重减弱，但在0.5 - 3.0 Hz范围内的稳态收缩幅度并无差异。这些结果与以下假设一致，即咖啡因诱导钙离子从肌浆网泄漏，并且这种钙离子可能通过钠/钙交换从细胞中排出。在1 - 5 mM浓度范围内，咖啡因似乎不会影响肌浆网对钙离子的摄取以及向释放位点的转运。
