Nozaki M, Sperelakis N
Department of Physiology and Biophysics, University of Cincinnati, College of Medicine, OH 45267-0576.
Eur J Pharmacol. 1991 May 2;197(1):57-62. doi: 10.1016/0014-2999(91)90364-v.
Cholera toxin (CTX) was used to test whether the presynaptic beta-adrenoceptors of guinea-pig mesenteric artery are coupled via stimulatory GTP-binding proteins. The vascular smooth muscle cells were electrically quiescent unless stimulated and had a mean resting potential of -68.7 +/- 2.8 mV (n = 16) and input resistance of 12.1 +/- 0.5 M omega (n = 4). Perivascular nerve stimulation with brief square pulses evoked excitatory junction potentials (EJPs) in the muscle cells. Isoproterenol (0.1 microM) enhanced the EJP amplitude without modifying the passive membrane properties of the muscle cells. The beta-blocker, propranolol (0.5 microM), prevented the effects of isoproterenol on EJP amplitude. The permeant analogue of cyclic AMP, 8-bromocAMP, also potentiated EJP amplitude. EJP amplitude was markedly enhanced by treatment of the isolated blood vessels with CTX (10 micrograms/ml for 1 h). The muscle cells became hyperpolarized (-74.6 +/- 2.1 mV, n = 5), and their input resistances were significantly reduced (8.2 +/- 0.5 M omega, n = 4). These effects of CTX persisted after washout. Addition of GM1 ganglioside (5 micrograms/ml) prevented the CTX effects. The CTX enhancement of EJP amplitude was not prevented by application of depolarizing current (ca. 0.5 nA) the muscle cells (to counter the hyperpolarization). These results suggest that CTX increases the neurotransmitter release from the nerve terminals; the hyperpolarization may be due to an increase in K+ conductance. These effects of CTX may be mainly due to elevation of cAMP in the nerve terminal and in the muscle cell.
霍乱毒素（CTX）被用于检测豚鼠肠系膜动脉突触前β - 肾上腺素能受体是否通过刺激性GTP结合蛋白偶联。血管平滑肌细胞在未受刺激时处于电静息状态，平均静息电位为 -68.7±2.8 mV（n = 16），输入电阻为12.1±0.5 MΩ（n = 4）。用短暂方形脉冲进行血管周围神经刺激可在肌肉细胞中诱发兴奋性接头电位（EJP）。异丙肾上腺素（0.1 μM）增强了EJP的幅度，而未改变肌肉细胞的被动膜特性。β - 阻滞剂普萘洛尔（0.5 μM）可阻止异丙肾上腺素对EJP幅度的影响。环磷酸腺苷（cAMP）的渗透性类似物8 - 溴环磷酸腺苷（8 - bromocAMP）也增强了EJP幅度。用CTX（10 μg/ml处理1小时）处理分离的血管后，EJP幅度显著增强。肌肉细胞发生超极化（-74.6±2.1 mV，n = 5），其输入电阻显著降低（8.2±0.5 MΩ，n = 4）。冲洗后，CTX的这些作用仍然存在。添加GM1神经节苷脂（5 μg/ml）可阻止CTX的作用。施加去极化电流（约0.5 nA）于肌肉细胞（以对抗超极化）并不能阻止CTX对EJP幅度的增强作用。这些结果表明，CTX增加了神经末梢的神经递质释放；超极化可能是由于钾离子电导增加所致。CTX的这些作用可能主要是由于神经末梢和肌肉细胞中cAMP水平的升高。
