Takano K, Yasufuku-Takano J, Teramoto A, Fujita T
Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Bunkyo-ku, Japan.
J Clin Invest. 1996 Nov 1;98(9):2033-41. doi: 10.1172/JCI119008.
The mechanisms of corticotropin-releasing hormone (CRH) induced excitation of ACTH-secreting adenoma cells were investigated using the perforated whole-cell clamp technique and intracellular Ca2+ concentration ([Ca2+]i) measurement. CRH depolarized ACTH-secreting adenoma cells by activating a nonselective cation current that showed slight inward rectification. This channel did not seem to be a member of the Ca(2+)-activated cation currents because it was activated even when the [Ca2+]i was chelated below 50 nM. The activation of the current was induced by protein kinase A-mediated pathways. By [Ca2+]i measurement, CRH increased [Ca2+]i of these cells dependently on voltage-gated Ca2+ current. This CRH-induced [Ca2+]i increase was abolished in Na(+)-free extracellular solution, but was not abolished by the addition of 5 microM tetrodotoxin to the extracellular solution. CRH-induced ACTH secretion from the cultured adenoma cells was also abolished in Na(+)-free extracellular solution, but not in tetrodotoxin-containing extracellular solution. These data indicate that a Na+ current (maybe the nonselective cation current) other than voltage-gated Na+ current plays an important role in CRH-induced [Ca2+]i increase and ACTH secretion. CRH also activated a nonselective cation current in nonadenoma human corticotrophs, suggesting that the activation of a nonselective cation current is a physiological mechanism of CRH-induced excitation in human corticotrophs.
利用穿孔全细胞钳技术和细胞内钙离子浓度（[Ca2+]i）测量法，研究了促肾上腺皮质激素释放激素（CRH）诱导促肾上腺皮质激素分泌性腺瘤细胞兴奋的机制。CRH通过激活一种显示轻微内向整流的非选择性阳离子电流，使促肾上腺皮质激素分泌性腺瘤细胞去极化。该通道似乎不是钙激活阳离子电流的成员，因为即使[Ca2+]i螯合至50 nM以下时它仍被激活。电流的激活是由蛋白激酶A介导的途径诱导的。通过[Ca2+]i测量发现，CRH依赖电压门控钙电流增加这些细胞的[Ca2+]i。在无钠细胞外溶液中，CRH诱导的[Ca2+]i增加被消除，但在细胞外溶液中添加5 μM河豚毒素时并未被消除。在无钠细胞外溶液中，CRH诱导培养的腺瘤细胞分泌促肾上腺皮质激素也被消除，但在含河豚毒素的细胞外溶液中则未被消除。这些数据表明，除电压门控钠电流外的一种钠电流（可能是非选择性阳离子电流）在CRH诱导的[Ca2+]i增加和促肾上腺皮质激素分泌中起重要作用。CRH还激活了非腺瘤性人促肾上腺皮质细胞中的非选择性阳离子电流，提示激活非选择性阳离子电流是CRH诱导人促肾上腺皮质细胞兴奋的一种生理机制。
