Figure 1. Comparison of sodium channel properties in the absence and presence of cholesterol. (A) Current traces in control (phosphatidylethanolamine (PE) and phosphatidylcholine (PC), 4:1 ratio) lipids and with 4% or 50%(weight/weight, corresponding to 7.3 and 65.3 mol%, respectively) cholesterol added. Synaptosomal fractions of human brain cortex were prepared, incorporated into planar bilayers in the presence of 250 nM batrachotoxin, and voltage-clamped (40 mV, filtered at 200 Hz). (B) Current-voltage plots for single sodium channels. Current amplitudes are averages of open-closed-open transitions measured manually. Circles = 4PE:1PC (no cholesterol), n = 19; triangles = 4%(weight/weight) cholesterol, n = 6; squares = 50%(weight/weight) cholesterol, n = 5. Error bars are SEM. Straight lines are linear regression fits of the data (slope conductances are 26.1 plus/minus 0.5, 25.5 plus/minus 0.3, and 24.6 plus/minus 0.2 pS). Data for 2%, 10%, and 20% cholesterol (not shown) yielded 27.6 plus/minus 1.1, 26.5 plus/minus 0.6, and 26.0 plus/minus 0.6 pS, respectively. Differences are not significant (values are within 95% confidence intervals). (C) Current through the sodium channels was averaged over time and plotted versus membrane potential. Circles = 4PE:1PC (no cholesterol), n = 6; triangles = 4%(weight/weight) cholesterol, n = 4; squares = 50%(weight/weight) cholesterol, n = 4. Error bars are SEM. Straight lines are linear regression fits of the data (slope conductances are 26.0 plus/minus 0.4, 27.9 + 1.0, and 26.1 plus/minus 0.8 pS); differences are not significant (values are within 95% confidence intervals).