Pelzer S, You Y, Shuba Y M, Pelzer D J
Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada.
Am J Physiol. 1997 Dec;273(6):H2539-48. doi: 10.1152/ajpheart.1997.273.6.H2539.
Here a comparison is made between adenosine 3',5'-cyclic monophosphate (cAMP)-activated Cl- current (ICl) density and activation time course in response to beta-adrenoceptor stimulation with isoproterenol and adenylyl cyclase activation with forskolin. Saturating concentrations of isoproterenol and forskolin failed to activate an ICl in guinea pig atrial as well as in rat and frog ventricular cardiomyocytes. In guinea pig ventricular cardiomyocytes, step application of 1 microM isoproterenol induced an ICl of -0.89 +/- 0.32 pA/pF (holding potential -40 mV, temperature 22 +/- 1 degrees C). ICl activation started after 3 +/- 1 s, was complete within 44 +/- 9 s, and was abolished after cell dialysis with the Rp diastereomer of adenosine 3',5'-cyclic monophosphothioate. Stimulation with increasing concentrations of forskolin (0.01-10 microM) increased ICl density and accelerated ICl activation. With 1 microM forskolin, ICl density was maximal (-0.57 +/- 0.30 pA/pF) but significantly smaller than that achieved with 1 microM isoproterenol. Although ICl density could not be further augmented by forskolin > 1 microM, current activation (latency 28 +/- 8 s, full activation after 112 +/- 8 s with 1 microM forskolin) was further accelerated by 3 and 10 microM forskolin. However, ICl activation with 10 microM forskolin was still slower than that with 1 microM isoproterenol. A low isoproterenol concentration (1 nM), which did not activate ICl by itself, accelerated the 1 microM forskolin-induced activation of ICl by 35%; this speeding up was abolished after cell dialysis with guanosine 5'-O-(2-thiodiphosphate). ICl deactivation after the washout of 1 microM forskolin or 1 microM isoproterenol followed a similar time course. After stimulation with 10 microM forskolin or 1 microM forskolin + 1 microM isoproterenol, but not with 1 microM forskolin + 1 nM isoproterenol, the decay of ICl was significantly delayed. These results indicate that both cAMP-dependent and cAMP-independent G protein pathways contribute to the regulation of guinea pig ventricular ICl.
本文比较了3',5'-环磷酸腺苷（cAMP）激活的氯离子电流（ICl）密度以及豚鼠心房肌细胞、大鼠和青蛙心室肌细胞在异丙肾上腺素刺激β-肾上腺素能受体和福斯高林激活腺苷酸环化酶时的激活时间进程。饱和浓度的异丙肾上腺素和福斯高林未能在豚鼠心房肌细胞以及大鼠和青蛙心室肌细胞中激活ICl。在豚鼠心室肌细胞中，施加1μM异丙肾上腺素可诱导产生-0.89±0.32 pA/pF的ICl（钳制电位-40 mV，温度22±1℃）。ICl激活在3±1秒后开始，44±9秒内完成，在用腺苷3',5'-环磷酸硫代酯的Rp非对映体对细胞进行透析后被消除。用浓度递增的福斯高林（0.01 - 10μM）刺激可增加ICl密度并加速ICl激活。使用1μM福斯高林时，ICl密度达到最大值（-0.57±0.30 pA/pF），但明显小于使用1μM异丙肾上腺素时达到的值。尽管浓度大于1μM的福斯高林不能进一步增加ICl密度，但3μM和10μM福斯高林可进一步加速电流激活（1μM福斯高林时潜伏期为28±8秒，112±8秒后完全激活）。然而，10μM福斯高林诱导的ICl激活仍比1μM异丙肾上腺素慢。低浓度的异丙肾上腺素（1 nM）本身不能激活ICl，但可使1μM福斯高林诱导的ICl激活加速35%；在用5'-O-(2-硫代二磷酸)鸟苷对细胞进行透析后，这种加速作用被消除。洗脱1μM福斯高林或1μM异丙肾上腺素后ICl的失活遵循相似的时间进程。在用10μM福斯高林或1μM福斯高林 + 1μM异丙肾上腺素刺激后，但用1μM福斯高林 + 1 nM异丙肾上腺素刺激后则不然，ICl的衰减明显延迟。这些结果表明，cAMP依赖性和cAMP非依赖性G蛋白途径均参与豚鼠心室ICl的调节。
