Valentijn J A, Vaudry H, Cazin L
European Institute for Peptide Research, CNRS URA 650, UA INSERM, University of Rouen, Mont-Saint-Aignan, France.
Neuroendocrinology. 1994 Jan;59(1):20-8. doi: 10.1159/000126633.
A patch-clamp study was conducted on cultured frog pituitary melanotrophs, in order to investigate the effects of adrenaline on the electrical activity of these cells. In the whole-cell configuration, adrenaline (1 microM) caused hyperpolarization that was accompanied by a fall in membrane input resistance and a blockage of spontaneous action potentials. Under voltage clamp, adrenaline elicited a net-outward current. The hyperpolarization became undetectable at a command voltage of -100 mV which corresponded to the equilibrium potential of potassium ions. The effect of adrenaline on membrane potential and spontaneous activity was blocked by the alpha 2-adrenergic receptor antagonist yohimbine (1-10 microM) but could not be mimicked by the alpha 2-adrenergic agonist clonidine (1-10 microM). In the cell-attached configuration, exposure of the extra-patch membrane to adrenaline increased the occurrence of single-channel currents with a slope conductance of 100 pS. The deduced reversal potential of these currents corresponded to the equilibrium potential of potassium ions. These results suggest that frog melanotrophs display an alpha 2-adrenergic receptor subtype coupled to potassium channels involved in hyperpolarization.
为了研究肾上腺素对培养的青蛙垂体黑素细胞电活动的影响，进行了一项膜片钳研究。在全细胞模式下，肾上腺素（1微摩尔）引起超极化，同时伴有膜输入电阻下降和自发动作电位受阻。在电压钳制下，肾上腺素引发外向净电流。在对应于钾离子平衡电位的-100毫伏指令电压下，超极化变得无法检测到。肾上腺素对膜电位和自发活动的影响被α2肾上腺素能受体拮抗剂育亨宾（1 - 10微摩尔）阻断，但α2肾上腺素能激动剂可乐定（1 - 10微摩尔）无法模拟这种作用。在细胞贴附模式下，将膜片外的膜暴露于肾上腺素会增加斜率电导为100皮西门子的单通道电流的出现频率。这些电流推导的反转电位对应于钾离子的平衡电位。这些结果表明，青蛙黑素细胞表现出一种与参与超极化的钾通道偶联的α2肾上腺素能受体亚型。
