Nieman C J, Eisner D A
J Gen Physiol. 1985 Dec;86(6):877-89. doi: 10.1085/jgp.86.6.877.
Membrane current and tension were measured in voltage-clamped sheep cardiac Purkinje fibers. Elevating the intracellular calcium concentration ([Ca2+]i) results in oscillations of membrane current and tension both at rest and during stimulation. During stimulation, an oscillatory transient inward current and an after contraction follow repolarization. We have examined the effects on the oscillations of changing the extracellular calcium concentration ([Ca2+]o) and of adding various drugs. In agreement with previous work, high concentrations of drugs that affect the sarcoplasmic reticulum, namely caffeine (10-20 mM), tetracaine (1 mM), and ryanodine (10 microM), abolish the oscillations. However, at lower concentrations, these three drugs have different effects on the oscillations. Caffeine (1-2 mM) decreases the oscillation amplitude but increases the frequency. Tetracaine (100-500 microM) has little effect on the magnitude of the oscillations but decreases their frequency. Ryanodine, at all concentrations used (0.1-10 microM), eventually abolishes the oscillations but, in doing so, decreases the magnitude, leaving the frequency unaffected. When [Ca2+]o was changed in order to vary [Ca2+]i, both the frequency and the magnitude of the oscillations always changed in the same direction. This suggests that these three drugs have effects in addition to just changing [Ca2+]i.
在电压钳制的绵羊心脏浦肯野纤维中测量膜电流和张力。提高细胞内钙浓度（[Ca2+]i）会导致静息和刺激期间膜电流和张力的振荡。在刺激期间，振荡性瞬时内向电流和后收缩跟随复极化。我们研究了改变细胞外钙浓度（[Ca2+]o）和添加各种药物对振荡的影响。与先前的工作一致，高浓度影响肌浆网的药物，即咖啡因（10 - 20 mM）、丁卡因（1 mM）和ryanodine（10 microM），可消除振荡。然而，在较低浓度下，这三种药物对振荡有不同的影响。咖啡因（1 - 2 mM）降低振荡幅度但增加频率。丁卡因（100 - 500 microM）对振荡幅度影响不大，但降低其频率。Ryanodine在所有使用的浓度（0.1 - 10 microM）下最终都会消除振荡，但在此过程中会降低幅度，而频率不受影响。当改变[Ca2+]o以改变[Ca2+]i时，振荡的频率和幅度总是朝相同方向变化。这表明这三种药物除了改变[Ca2+]i之外还有其他作用。
