Tamarina Natalia A, Kuznetsov Andrey, Fridlyand Leonid E, Philipson Louis H
Dept. of Medicine, University of Chicago, IL 60637, USA.
Am J Physiol Endocrinol Metab. 2005 Oct;289(4):E578-85. doi: 10.1152/ajpendo.00054.2005. Epub 2005 Jul 12.
The delayed-rectifier (voltage-activated) K(+) conductance (K(V)) in pancreatic islet beta-cells has been proposed to regulate plasma membrane repolarization during responses to glucose, thereby determining bursting and Ca(2+) oscillations. Here, we verified the expression of K(V)2.1 channel protein in mouse and human islets of Langerhans. We then probed the function of K(V)2.1 channels in islet glucose responses by comparing the effect of hanatoxin (HaTx), a specific blocker of K(V)2.1 channels, with a nonspecific K(+) channel blocker, tetraethylammonium (TEA). Application of HaTx (1 microM) blocked delayed-rectifier currents in mouse beta-cells, resulting in a 40-mV rightward shift in threshold of activation of the voltage-dependent outward current. In the presence of HaTx, there was negligible voltage-activated outward current below 0 mV, suggesting that K(V)2.1 channels form the predominant part of this current in the physiologically relevant range. We then employed HaTx to study the role of K(V)2.1 in the beta-cell Ca(2+) responses to elevated glucose in comparison with TEA. Only HaTx was able to induce slow intracellular Ca(2+) concentration (Ca(2+)) oscillations in cells stimulated with 20 mM glucose, whereas TEA induced an immediate rise in Ca(2+) followed by rapid oscillations. In human islets, HaTx acted in a similar fashion. The data were analyzed using a detailed mathematical model of ionic flux and Ca(2+) regulation in beta-cells. The results can be explained by a specific HaTx effect on the K(V) current, whereas TEA affects multiple K(+) conductances. The results underscore the importance of K(V)2.1 channel in repolarization of the pancreatic beta-cell plasma membrane and its role in regulating insulin secretion.
胰腺胰岛β细胞中的延迟整流（电压激活）钾离子电导（K(V)）被认为在对葡萄糖的反应过程中调节质膜复极化，从而决定动作电位发放和钙离子振荡。在此，我们验证了K(V)2.1通道蛋白在小鼠和人类胰岛中的表达。然后，我们通过比较K(V)2.1通道的特异性阻滞剂哈那毒素（HaTx）与非特异性钾离子通道阻滞剂四乙铵（TEA）对胰岛葡萄糖反应的影响，来探究K(V)2.1通道的功能。应用HaTx（1微摩尔）可阻断小鼠β细胞中的延迟整流电流，导致电压依赖性外向电流激活阈值向右移动40毫伏。在存在HaTx的情况下，在0毫伏以下几乎没有电压激活的外向电流，这表明K(V)2.1通道在生理相关范围内构成了该电流的主要部分。然后，我们使用HaTx与TEA比较，研究K(V)2.1在β细胞对葡萄糖升高的钙离子反应中的作用。只有HaTx能够在20毫摩尔葡萄糖刺激的细胞中诱导缓慢的细胞内钙离子浓度（[Ca(2+)]i）振荡，而TEA则诱导[Ca(2+)]i立即升高，随后快速振荡。在人类胰岛中，HaTx的作用方式类似。使用β细胞离子通量和钙离子调节的详细数学模型对数据进行了分析。结果可以用HaTx对K(V)电流的特异性作用来解释，而TEA影响多种钾离子电导。这些结果强调了K(V)2.1通道在胰腺β细胞质膜复极化中的重要性及其在调节胰岛素分泌中的作用。
