Guinea-pig isolated trachealis: the effects of charybdotoxin on mechanical activity, membrane potential changes and the activity of plasmalemmal K(+)-channels.
作者信息
Murray M A, Berry J L, Cook S J, Foster R W, Green K A, Small R C
机构信息
Department of Physiological Sciences, University of Manchester.
A study has been made, in guinea-pig isolated trachealis, of the effects of charybdotoxin in modulating (a) the activity of large conductance K(+)-channels, (b) the spontaneous electrical activity of intact cells and (c) the mechanical effects of some bronchodilator drugs. 2. Single smooth muscle cells were isolated from guinea-pig trachealis by enzymic digestion and were studied by the patch clamp recording technique. Recordings were made from outside-out plasmalemmal patches when the medium bathing the external surface of the patches contained 1.2 mM Ca2+ and 6 mM K+ while that bathing the cytosolic surface contained 0.1 microM Ca2+ and 140 mM K+. Charybdotoxin (100 nM), applied to the external surface of patches held at 0 mV, abolished the unitary currents associated with the opening of large conductance K(+)-channels. 3. Opened segments of guinea-pig trachea were used for the simultaneous recording of membrane potential and tension changes. In these experiments charybdotoxin (100 nM) caused the conversion of spontaneous electrical slow waves into spike-like action potentials. This effect was accompanied by a very small reduction in resting membrane potential. 4. Tissue bath recording showed that charybdotoxin (100 nM) increased the spontaneous mechanical tone of the tissue, antagonized (2.8 fold in each case) the relaxant actions of isoprenaline and theophylline but did not antagonize the relaxant actions of cromakalim or RP 49356. 5. It is concluded that charybdotoxin is an effective inhibitor of large conductance K(+)-channels in guinea-pig trachealis cells. The ability of charybdotoxin to convert spontaneous slow waves into spike-like action potentials suggests that the large, charybdotoxin-sensitive, K+-channels play an important role in determining the strong outward rectifying behaviour of the cells. The ability of charybdotoxin to antagonize isoprenaline and theophylline, but not to antagonize cromakalim and RP 49356, suggests that opening of the large conductance, charybdotoxin-sensitive K+-channel is implicated in the action of the former but not the latter pair of bronchodilator drugs.
摘要
在豚鼠离体气管上进行了一项研究，观察了蝎毒素对以下方面的调节作用：(a) 大电导钾通道的活性；(b) 完整细胞的自发电活动；(c) 某些支气管扩张药物的机械效应。2. 通过酶消化从豚鼠气管分离出单个平滑肌细胞，并用膜片钳记录技术进行研究。当贴片外表面的浴液含有1.2 mM Ca2+和6 mM K+，而贴片胞质表面的浴液含有0.1 μM Ca2+和140 mM K+时，从外向内的质膜片进行记录。将蝎毒素（100 nM）施加到保持在0 mV的贴片外表面，消除了与大电导钾通道开放相关的单位电流。3. 使用豚鼠气管的开放节段同时记录膜电位和张力变化。在这些实验中，蝎毒素（100 nM）使自发电慢波转变为尖峰样动作电位。这种效应伴随着静息膜电位非常小的降低。4. 组织浴记录显示，蝎毒素（100 nM）增加了组织的自发机械张力，拮抗了异丙肾上腺素和茶碱的舒张作用（每种情况均为2.8倍），但不拮抗克罗卡林或RP 49356的舒张作用。5. 得出结论，蝎毒素是豚鼠气管细胞中大电导钾通道的有效抑制剂。蝎毒素将自发慢波转变为尖峰样动作电位的能力表明，对蝎毒素敏感的大钾通道在决定细胞强烈的外向整流行为中起重要作用。蝎毒素拮抗异丙肾上腺素和茶碱，但不拮抗克罗卡林和RP 49356的能力表明，大电导、对蝎毒素敏感的钾通道的开放与前一对支气管扩张药物的作用有关，而与后一对无关。
