Wang Q, Hogg R C, Large W A
Department of Pharmacology and Clinical Pharmacology, St George's Hospital Medical School, London, UK.
Pflugers Arch. 1993 Apr;423(1-2):28-33. doi: 10.1007/BF00374957.
Membrane currents were recorded with the perforated-patch method with a low-chloride (35 mM) pipette solution in isolated smooth muscle cells of the rabbit ear artery. At a holding potential of -50 mV in potassium-free conditions spontaneous inward single-channel currents were observed and noradrenaline evoked a noisy inward current, which appeared to be comprised of the spontaneous currents. The reversal potential (Vr) of the spontaneous channel and noradrenaline-induced current was not affected in anion-substitution experiments but Vr was altered when external Na+ was replaced with choline or TRIS. The relationship between clamp potential and spontaneous single-channel current amplitude was linear and the mean unitary conductance was 28 pS. Caffeine, which releases calcium from the sarcoplasmic reticulum, and the calcium ionophore ionomycin activated the cation current and also blocked the response to noradrenaline. Spontaneous channel current activity and the noradrenaline-induced current were blocked when external NaCl was replaced with 89 mM CaCl2. The response to noradrenaline was blocked by prazosin but was not affected by yohimbine and therefore the response is mediated by alpha 1-adrenoceptors. It is concluded that in rabbit ear artery smooth muscle cells there is a calcium-activated cation channel of 28 pS conductance, which is relatively impermeable to calcium but can be activated by noradrenaline.
采用穿孔膜片钳法，使用低氯（35 mM）的微电极内液，在兔耳动脉分离的平滑肌细胞中记录膜电流。在无钾条件下，钳制电位为 -50 mV 时，可观察到自发内向单通道电流，去甲肾上腺素可诱发一种嘈杂的内向电流，该电流似乎由自发电流组成。在阴离子置换实验中，自发通道和去甲肾上腺素诱导电流的反转电位（Vr）不受影响，但当用胆碱或三羟甲基氨基甲烷替代细胞外 Na⁺ 时，Vr 发生改变。钳制电位与自发单通道电流幅度之间的关系呈线性，平均单位电导为 28 pS。咖啡因可从肌浆网释放钙，钙离子载体离子霉素可激活阳离子电流，同时也可阻断对去甲肾上腺素的反应。当用 89 mM CaCl₂ 替代细胞外 NaCl 时，自发通道电流活动和去甲肾上腺素诱导电流均被阻断。对去甲肾上腺素的反应可被哌唑嗪阻断，但不受育亨宾影响，因此该反应由α₁ - 肾上腺素能受体介导。结论是，在兔耳动脉平滑肌细胞中存在一种电导为 28 pS 的钙激活阳离子通道，该通道对钙相对不通透，但可被去甲肾上腺素激活。
