Parameters affecting the slow inward channel repriming process in frog atrium.

1. The time of recovery (from the inactivation) of the slow inward current was studied in the frog atrium, using the double sucrose gap voltage clamp technique. 2. The 'repriming' process was found to be distinct from the current inactivation, and to depend on experimental protocol: double pulses given at low frequencies (at 'rest') gave a faster recovery time when compared to recovery during constant stimulation, with interposed stimuli monitoring the recovery. Longer durations of the clamp pulses led to a faster recovery process. 3. Changing the holding potential of the membrane (with double pulses to the same absolute membrane potential monitoring the recovery process) greatly affect the repriming with depolarized levels slowing down the process. 4. The recovery time was fastest following clamp pulses to intermediate membrane potentials (in the plateau range). This was determined by double pulses, from a constant hold potentials, to different levels. 5. Decreasing extracellular Ca prolonged, and increasing Ca enhanced the recovery process. 6. The recovery process was markedly slowed down in Na or in K-free solutions. 7. The recovery process was enhanced in solutions with a raised concentration of Mg or H ions (lower pH). In higher Mg solutions, the inactivation of the slow inward current was slower. 8. It is proposed that the recovery process is sensitive to alterations in intracellular Ca ions and to variations in extracellular surface charges. The possible implications are discussed.