A comparative electrophysiological study of enzymatically isolated single cells and strips of frog ventricle.

Single heart cells were obtained from frog ventricle using an enzymatic dispersion technique. The whole cell variation of the patch clamp technique was used to monitor action potential and cell membrane currents. The clamp circuit could be switched electronically between voltage and current clamp modes. The effects of seal leakage currents were to depolarize the cell, reduce the amplitude of the plateau, and lengthen the action potential duration. A scheme to compensate for these currents is presented. The membrane currents obtained from the single cell under voltage clamp conditions were compared to those obtained from multicellular preparations using the single sucrose gap technique. Hyperpolarizing clamps showed time-dependent, depletion-related K+ currents for the multicellular preparation, whereas for the single cell no such currents were observed. The absence of extracellular accumulation or depletion of K+ in the single cell was confirmed by the lack of post-clamp afterpotentials or changes in resting potential following a train of frequently elicited action potentials. The TTX-insensitive inward current was relatively faster in the single cell, compared to that measured in the multicellular preparation. A delayed time-dependent outward current was observed in the positive potential range for both single and multicellular preparations. The isochronal current-voltage (I-V) relations obtained at 400 ms were N-shaped for both preparations, but was more negative for the single cell at potentials positive to -20 mV. The results indicate a strong similarity between membrane currents obtained in single and multicellular preparations. The differences in the currents in the two preparations are due in large part to accumulation or depletion of K+ in the extracellular space.