RELATIONSHIP BETWEEN STEADY-STATE ACTIVATION AND AVAILABILITY OF CARDIAC SODIUM-CHANNEL - EVIDENCE OF UNCOUPLING

The coupling between steady-state activation and availability from ina ctivation was characterized for the cardiac Na+ channel. To evaluate t his coupling, we plotted the relationship between the conductance and availability curve midpoint potentials measured in 92 rat ventricular cardiomyocytes and applied a correlation analysis. We found a high cor relation between the midpoints (correlation coefficient = 0.86, slope = 0.95) within the availability midpoint potential range positive to - 100 mV. In contrast, the midpoints were not correlated in the myocytes (37 of 92 cells) having midpoint potential negative to -100 mV, indic ating an uncoupling between activation and availability.