FIGURE 3.
Cholesterol loading alters both Vpkc and charge density in a concentration-dependent manner. A, shown is a plot of the mean Vpkc (mV) versus the membrane cholesterol concentration (pmol/μg of protein). In untreated cells (▪, membrane cholesterol 7.4 pmol/μg of protein; n = 39), the mean Vpkc was approximately –72 mV. In MβCD-treated cells (⋄, membrane cholesterol 2.8 pmol/μg of protein; n = 25), the mean Vpkc was –17 mV. The series of cholesterol-treated cell groups (♦, n = 10, 7, 11, 19, and 8) had membrane cholesterol concentrations ranging from 14.4 to 30.4 pmol/μg protein and Vpkc values ranging from –103 to –143 mV. A significant hyperpolarizing shift was seen in Vpkc for each group of cholesterol-loaded cells relative to the control (p < 0.0001), and the shifts became larger as membrane cholesterol concentration increased. A linear regression function has been fit to the control and cholesterol-loading data (y = –3.26x – 52.7, R2 = 0.923). B, the curves represent the mean charge moved (pC) versus voltage (mV) for cholesterol-loaded cells at membrane cholesterol concentrations of 14.4 (solid line, n = 10), 20.7 (dashed line, n = 7), 23.5 (dotted line, n = 19) and 30.4 pmol/μg of protein (dash-dotted line, n = 7). The charge at Vpkc is labeled for each treatment (♦, ▪, ▴, and •, respectively). The total charge movement, represented by the height of the curve, decreased as membrane cholesterol concentration increased. C, as the membrane cholesterol concentration was increased, the mean charge density (fC/pF) decreased. The mean charge densities for untreated cells (▪, n = 39) and MβCD-treated cells (⋄, n = 25) were 16.1 and 17.3 fC/pF, respectively. The series of cholesterol-treated cell groups (♦, n = 10, 7, 11, 19, and 7) had mean charge densities ranging from 5.2 to 12.9 fC/pF. A linear regression function has been fit to the control and cholesterol-loading data (y = –0.486x + 19.8, R2 = 0.952). In A and C, horizontal and vertical error bars represent 2 S.E. in either direction relative to the mean.