Tabares L, López-Barneo J, de Miguel C
Biochim Biophys Acta. 1985 Mar 28;814(1):96-102. doi: 10.1016/0005-2736(85)90423-7.
Current flowing through single Ca- and voltage-activated K channels has been recorded from cell-attached and inside-out excised membrane patches of cultured Y-1 adrenocortical cells. In intact cells, single-channel current amplitude and the time a channel stays in the open state increase with membrane depolarization. In excised patches bathed in symmetrical 130 mM K solutions, single-channel conductance is 170 pS. This value is constant in the membrane potential range of +/- 50 mV but decreases at larger hyper- and depolarizations. Channel open probability is heavily influenced by the concentration of ionic Ca at the inner surface of the membrane in the range between 0.01 and 10 microM. When internal Ca concentration is close to 0.01 microM, channels are usually closed even at large depolarizing voltages. With larger Ca concentrations, channel open probability increases and its voltage dependence is greater. These channels are uniformly distributed in the plasma membrane, since one to four channels were seen in more than 99% of the patches isolated in this study. There are previous reports suggesting a role for calcium ions in the secretory response of adrenocortical cells to ACTH. Therefore, it is possible that, as in other endocrine cells, these K channels modulate Ca influx across the plasma membrane and thus contribute to regulate steroid biosynthesis and release.
从培养的Y-1肾上腺皮质细胞的细胞贴附式和内面向外式膜片上记录了单个钙激活和电压激活钾通道中的电流。在完整细胞中，单通道电流幅度和通道保持开放状态的时间随膜去极化而增加。在对称的130 mM K溶液中浸泡的膜片中，单通道电导为170 pS。该值在+/- 50 mV的膜电位范围内恒定，但在更大的超极化和去极化时降低。通道开放概率在膜内表面离子钙浓度在0.01至10 microM范围内时受到很大影响。当内部钙浓度接近0.01 microM时，即使在大的去极化电压下通道通常也是关闭的。随着钙浓度增加，通道开放概率增加且其电压依赖性更大。这些通道均匀分布在质膜中，因为在本研究分离的超过99%的膜片中观察到一到四个通道。以前有报道表明钙离子在肾上腺皮质细胞对促肾上腺皮质激素的分泌反应中起作用。因此，与其他内分泌细胞一样，这些钾通道可能调节钙跨质膜的内流，从而有助于调节类固醇生物合成和释放。
