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

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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.