Low affinity, concentration-dependent block of hK V 1.2 channels by SA8 was determined by fitting a straight line to the reciprocal of the remaining current fraction (1/RCF) plotted as a function of SA8 concentration. The remaining current fraction (RCF) was calculated as I/I 0 , where I 0 is the peak current in the absence and I is the peak current at the equilibrium block in the presence of SA8 at concentrations of 0.01, 0.1, 1, and 10 M (filled circles). Points on the linear concentration–response curve represent the mean of four independent measurements where the error bars represent the standard error of mean (SEM). The line was drawn using linear least squares fit and the reciprocal of the slope of the best fit yielded an IC 50 of 40.8 ± 4.9 M.
