Vignali Sheila, Leiss Veronika, Karl Rosi, Hofmann Franz, Welling Andrea
Institut für Pharmakologie und Toxikologie, TU München, Biedersteiner Strasse 29, D-80802 München, Germany.
J Physiol. 2006 May 1;572(Pt 3):691-706. doi: 10.1113/jphysiol.2005.102368.
Insulin and glucagon are the major hormones of the islets of Langerhans that are stored and released from the B- and A-cells, respectively. Both hormones are secreted when the intracellular cytosolic Ca2+ concentration ([Ca2+]i) increases. The [Ca2+]i is modulated by mutual inhibition and activation of different voltage-gated ion channels. The precise interplay of these ion channels in either glucagon or insulin release is unknown, owing in part to the difficulties in distinguishing A- from B-cells in electrophysiological experiments. We have established a single-cell RT-PCR method to identify A- and B-cells from the mouse. A combination of PCR, RT-PCR, electrophysiology and pharmacology enabled us to characterize the different sodium and calcium channels in mouse islet cells. In both A- and B-cells, 60% of the inward calcium current (I(Ca)) is carried by L-type calcium channels. In B-cells, the predominant calcium channel is Ca(v)1.2, whereas Ca(v)1.2 and Ca(v)1.3 were identified in A-cells. These results were confirmed by using mice carrying A- or B-cell-specific inactivation of the Ca(v)1.2 gene. In B-cells, the remaining I(Ca) flows in equal amounts through Ca(v)2.1, Ca(v)2.2 and Ca(v)2.3. In A-cells, 30 and 15% of I(Ca) is due to Ca(v)2.3 and Ca(v)2.1 activity, respectively, whereas Ca(v)2.2 current was not found in these cells. Low-voltage-activated T-type calcium channels could not be identified in A- and B-cells. Instead, two TTX-sensitive sodium currents were found: an early inactivating and a residual current. The residual current was only recovered in a subpopulation of B-cells. A putative genetic background for these currents is Na(v)1.7.
胰岛素和胰高血糖素是胰岛的主要激素，分别由B细胞和A细胞储存并释放。当细胞内胞质Ca2+浓度（[Ca2+]i）升高时，这两种激素都会分泌。[Ca2+]i受不同电压门控离子通道的相互抑制和激活调节。这些离子通道在胰高血糖素或胰岛素释放中的精确相互作用尚不清楚，部分原因是在电生理实验中区分A细胞和B细胞存在困难。我们建立了一种单细胞RT-PCR方法来从小鼠中鉴定A细胞和B细胞。PCR、RT-PCR、电生理和药理学的结合使我们能够表征小鼠胰岛细胞中不同的钠通道和钙通道。在A细胞和B细胞中，60%的内向钙电流（I(Ca)）由L型钙通道携带。在B细胞中，主要的钙通道是Ca(v)1.2，而在A细胞中鉴定出了Ca(v)1.2和Ca(v)1.3。通过使用携带Ca(v)1.2基因A细胞或B细胞特异性失活的小鼠，证实了这些结果。在B细胞中，剩余的I(Ca)等量地通过Ca(v)2.1、Ca(v)2.2和Ca(v)2.3流动。在A细胞中，30%和15%的I(Ca)分别归因于Ca(v)2.3和Ca(v)2.1的活性，而在这些细胞中未发现Ca(v)2.2电流。在A细胞和B细胞中未鉴定出低电压激活的T型钙通道。相反，发现了两种对TTX敏感的钠电流：一种早期失活电流和一种残余电流。残余电流仅在一部分B细胞中恢复。这些电流的一个推定遗传背景是Na(v)1.7。
