Tanaka H, Clark R B, Giles W R
Department of Medicine, University of Calgary, Alberta, Canada.
Proc Biol Sci. 1996 Mar 22;263(1368):241-8. doi: 10.1098/rspb.1996.0038.
The kinetics of onset and the intracellular biochemical signalling mechanisms which are responsible for the positive chronotropic effect of sympathetic stimulation in rabbit cardiac pacemaker cells were examined by using flash photolysis of caged isoproterenol (ISO) and cyclic AMP (cAMP). When caged ISO (10 microM) was present in the superfusate, a single ultraviolet flash caused gradual increases in the spontaneous beating frequency and action potential height of S-A node cells. Both these effects developed after an initial latency of approximately 5 s. Photorelease of ISO also increased the L-type Ca2+ current (ICa-L) with a time-course similar to that of the changes in action potential waveform and heart rate. All of these ISO-induced effects were blocked completely by 1 microM propranolol, demonstrating that they were beta-adrenergic responses. Flash photolysis of caged cAMP (50 microM) also resulted in increased firing frequency and ICa-L. However, these responses to cAMP developed with little or no latency. Intracellular dialysis with a selective inhibitor of the cAMP-dependent protein kinase, Rp-cAMPS, completely abolished the increase in ICa-L demonstrating that it is mediated exclusively via cAMP-dependent activation of protein kinase A, as opposed to a direct G-protein mediated mechanism.
通过使用笼蔽异丙肾上腺素（ISO）和环磷酸腺苷（cAMP）的闪光光解技术，研究了家兔心脏起搏细胞中交感神经刺激产生正性变时效应的起始动力学和细胞内生化信号传导机制。当灌流液中存在笼蔽ISO（10微摩尔）时，单次紫外闪光可使窦房结细胞的自发搏动频率和动作电位高度逐渐增加。这两种效应在最初约5秒的潜伏期后出现。ISO的光释放还增加了L型钙电流（ICa-L），其时间进程与动作电位波形和心率变化相似。所有这些ISO诱导的效应均被1微摩尔普萘洛尔完全阻断，表明它们是β-肾上腺素能反应。笼蔽cAMP（50微摩尔）的闪光光解也导致发放频率和ICa-L增加。然而，这些对cAMP的反应几乎没有潜伏期或没有潜伏期就出现了。用cAMP依赖性蛋白激酶的选择性抑制剂Rp-cAMPS进行细胞内透析，完全消除了ICa-L的增加，表明它完全是通过cAMP依赖性激活蛋白激酶A介导的，而不是直接的G蛋白介导机制。
