Shonnard P Y, Sanders K M
Department of Physiology, University of Nevada School of Medicine, Reno 89557.
Am J Physiol. 1990 Jan;258(1 Pt 1):G12-5. doi: 10.1152/ajpgi.1990.258.1.G12.
By using isolated gastric muscle cells of Bufo marinus, others have studied the mechanism of action of muscarinic agonists and substance P (SP). To compare responses of isolated cells with those of intact muscles, we have studied the effects of acetylcholine (ACh) and SP on membrane potentials of circular muscle cells in strips of intact muscle from the toad gastric corpus region. These cells had average resting potentials of -69 +/- 0.7 mV. Membrane potential rhythmically depolarized, producing slow waves at an average frequency of 1/min and average amplitude of 25 +/- 2.2 mV. The major effect of ACh (10(-7) to 10(-4) M) was chronotropic; the frequency of slow waves was increased by 88 +/- 11% by 10(-6) M ACh. The amplitudes and rates of rise of slow waves were decreased by ACh. SP had effects similar to ACh; its major effect was chronotropic. The data suggest that ACh and SP primarily affect the pacemaker mechanism in gastric muscles. Since rhythmicity is apparently not expressed in isolated gastric myocytes, it is possible that this effect of these agonists may have been missed in studies of dispersed cells. Our data suggest that the excitatory effects of ACh and SP on contractions may be due to summation of Ca2+ signals, a partial tetanus-like effect.
通过使用海蟾蜍分离的胃肌细胞，其他人研究了毒蕈碱激动剂和P物质（SP）的作用机制。为了比较分离细胞与完整肌肉的反应，我们研究了乙酰胆碱（ACh）和SP对蟾蜍胃体区域完整肌肉条中环行肌细胞膜电位的影响。这些细胞的平均静息电位为-69±0.7 mV。膜电位有节律地去极化，产生平均频率为1次/分钟、平均幅度为25±2.2 mV的慢波。ACh（10⁻⁷至10⁻⁴ M）的主要作用是变时性的；10⁻⁶ M ACh使慢波频率增加88±11%。ACh使慢波的幅度和上升速率降低。SP具有与ACh相似的作用；其主要作用是变时性的。数据表明，ACh和SP主要影响胃肌中的起搏机制。由于在分离的胃肌细胞中显然没有表现出节律性，这些激动剂的这种作用在分散细胞的研究中可能被遗漏了。我们的数据表明，ACh和SP对收缩的兴奋作用可能是由于Ca²⁺信号的总和，一种部分强直性的作用。
