Figure 5. Effect of cholesterol on sodium channel activation. Filled circles denote data before and open squares after addition of 680 micro Meter pentobarbital. Data were calculated by averaging the averaged data from each membrane. Curves represent least-squares fits of a Boltzmann function to the averaged data (solid line - controls; dotted line - pentobarbital). Error bars denote SEM. (A) 4PE:1PC; nine experiments and 11 channels. Fits yielded potentials of half-maximal fractional open time (midpoint potentials) of 77.6 and 93.8 mV for controls and pentobarbital, respectively (shift of 16.2 mV). [24]. (B) 4% cholesterol; four experiments and five channels. Midpoint potential was shifted 6.1 mV by pentobarbital. (C) 10% cholesterol; three experiments and seven channels. Midpoint potential was shifted -13.1 mV by pentobarbital. (D) 50% cholesterol; four experiments and eight channels. Midpoint potential was shifted -11.0 mV by pentobarbital.