Analysis of the Gating Mechanism of Cardiac Ca Channel by Long Recorder

交感儿茶酚胺增加心肌的l型钙电流。迄今为止，使用膜片钳技术进行的单通道研究已经确定，这种增加是由于总打开概率的增加，该概率由含电流扫描的速率决定（可用性，Ps）。目前的研究关注的问题是-受体激动剂如何改变Ps和每次含电流扫描（Po）的开放概率。用酶法分离豚鼠心室肌细胞，并用高钾天冬氨酸溶液进行灌注。通过100mm含ba的移液器记录仅含有一个功能活性通道的细胞贴片上的单Ca通道电流。将ISO加入到过浓液中，并将BAY K 8644应用于灌注液或移液液中。在100 nM浓度下，异丙肾上腺素（ISO）可明显减慢Ca通道的门通过程并增加Ps，即使在0.01 mM和0.1 mM浓度下，ISO也只增加Ps，其主要变化是Ps的增加与100 nM相似。在BAY k8644存在的情况下，ISO再次增加了通道的可用性。我们发现，在有BAY k存在的非空白扫描中，ISO也增加了Po，在100 nM处Po增加了ISO约60%。因此，通道磷酸化可能有利于二氢吡啶类药物与通道的结合。

The sympathetic catecholamines increase L-type Ca current in cardiac muscle. Hitherto single channel studies with patch clamp technique have established that the increase is due to an increase in the total open probability determined by the rate of current-containing sweeps (availability, Ps). Present study concerns with the problem how the beta-agonists modify Ps and the open probability in each current-containing sweep (Po). Ventricular myocytes were isolated enzymatically from guinea-pig and superfused with high-K aspartate solution. Single Ca channel currents were recorded from cell-attached patches containing only one functionally active channel by 100 mm Ba-containing pipettes. ISO were added to the superfusate and BAY K 8644 was applied either to the perfusate or to the pipette solution. Isoprenaline (ISO) at 100 nM modulated ecusively slow gating processes of the Ca channel and increased Ps. ISO increased excusively Ps even at 0.01 mM and 0.1 mM. The major changes at these high concentration was the increase in Ps similarly with 100 nM. In the presence of BAY K 8644 ISO again increased the channel availability. We found that ISO also increases Po in the nonblank sweeps in the presence of BAY K. Po was increased by ISO by about 60% at 100 nM. Thus, the channel phosphorylation may favor the binding of dihydropyridine drugs to the channel.