Modified gating behaviour of aconitine treated single sodium channels from adult cardiac myocytes

Currents through single Na channels of ventricular cells from adult mouse and guinea pig hearts were studied using the patch clamp technique. Under control conditions the majority of openings is brief and a clustering at the beginning of the depolarizing pulse can be observed. Only between 1 and 8% of the sweeps show long lasting bursts. The bursting may account for a second slow phase of decay of macroscopic currents. In the presence of aconitine in the pipette up to 80% of the sweeps showed bursts underlying the slow inactivation of aconitine modified macroscopic currents. The mean open times are unchanged but the number of openings per sweep is dramatically increased due to aconitine. It is discussed that Na channels may function in different "modes". One mode is characterized by a fast transition into an absorbing state the other one by frequent reopenings ("bursts"). aconitine favours the "bursting" mode.