Figure 8.

Quantification of surface expressions of Ca_V1.2 splice variants. (A) The Q_on measured by tail protocol from HEK 293 cells transfected with Ca_V1.2 calcium channel isoforms is shown. Representative traces (top panel) of step depolarizations to the reversal potential (E_rev) were elicited for 20 ms with a subsequent hyperpolarizing pulse of −50 mV for 10 ms, during which the gating current was measured. The movement of the total charge, ON-gating (Q_on), during depolarization, was recorded in 5-mM Ba²⁺. A magnification of exemplary Q_on currents (bottom, left panel) for isoforms 1/8a_1a/8 (left) and 1/8_1a/8a (right) is shown. Q_on was normalized to its capacitance (pF). A box-plot for ON-gating currents is given (bottom, left panel). Data show median, 25, and 75% percentiles, minimum and maximum. An unpaired t-test was used for significance testing, ^∗p < 0.05, ^∗∗p < 0.01. (B) The GV relationship obtained from tail currents that were normalized to their cell capacitance is shown. (C) The surface protein levels of N-terminal Ca_V1.2 splice variants in transfected HEK 293 cells are shown. Representative western blot and quantifications of biotinylated surface 1/8a, 1/8, 1a/8a, and 1a/8 isoforms overexpressed in HEK 293 cells are shown (n = 4; left panel). An unpaired t-test was used for significance testing, ^∗p < 0.05 and p^∗∗ < 0.01 (population data; right panel).