1. Na+ current kinetics were studied in isolated atrial myocytes from the adult cat using the single suction‐pipette voltage‐clamp technique. 2. Current‐voltage and conductance‐voltage relationships were similar to those described in other cardiac myocyte preparations. 3. Analysis of Na+ current decay using single‐pulse, double‐pulse and tail current measurements were in agreement and demonstrate a second‐order process of current decay. 4. Voltage dependence of steady‐state inactivation curves was not symmetrical, having an inflexion at about ‐90 mV. These results suggest more than a single inactivation process for Na+ channel in the negative potential region. 5. Recovery of Na+ current from inactivation had a sigmoid time course: an initial slow component (delay) followed by a fast and then a second slow component. Increasing the pre‐pulse duration slowed the time course of recovery. 6. Taken together, the results were consistent with the presence of multiple inactivated states for the atrial myocyte Na+ channel.
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