Sanchez J A, Vergara J
Department of Physiology, University of California School of Medicine, Los Angeles 90024.
Am J Physiol. 1994 May;266(5 Pt 1):C1291-300. doi: 10.1152/ajpcell.1994.266.5.C1291.
Action potentials and intracellular Ca2+ transients were monitored in current-clamped segments of frog skeletal muscle fibers using the triple vaseline-gap technique. Calcium signals were measured with the fluorescent indicator rhod 2. Action potentials produced a transient increase in intracellular Ca2+ that was estimated, by deconvolution of the fluorescence signals, to range between 3 and 12 microM. The comparative effects of flash photolysis of caged adenosine 3',5'-cyclic monophosphate (cAMP) and caged ATP on action potentials and Ca signals in muscle were investigated. The photorelease of both nucleotides produced a reduction in the amplitude of the afterpotential that follows the spike. Photorelease of cAMP and ATP prolonged the rate of decay of the Ca signals. No changes in either the rate of rise or in the latent period between stimulation and onset of the Ca signal were observed. Release of cAMP reduced the amplitude of Ca signals, whereas release of ATP had the opposite effect. Our results show that cAMP and ATP, released above their endogenous levels, modulate intracellular Ca2+ release. The cAMP modulation is more significant and may be of physiological importance.
采用三重凡士林间隙技术，在蛙骨骼肌纤维的电流钳制节段中监测动作电位和细胞内Ca2+瞬变。使用荧光指示剂罗丹明2测量钙信号。动作电位使细胞内Ca2+产生短暂增加，通过对荧光信号进行去卷积估计，其范围在3至12微摩尔之间。研究了笼化腺苷3',5'-环磷酸单酯（cAMP）和笼化ATP的闪光光解对肌肉动作电位和钙信号的比较影响。两种核苷酸的光释放均使锋电位后的后电位幅度降低。cAMP和ATP的光释放延长了钙信号的衰减速率。未观察到钙信号的上升速率或刺激与钙信号起始之间的潜伏期有任何变化。cAMP的释放降低了钙信号的幅度，而ATP的释放则产生相反的效果。我们的结果表明，高于内源性水平释放的cAMP和ATP可调节细胞内Ca2+释放。cAMP的调节作用更为显著，可能具有生理重要性。
