Alternative Splicing of the Voltage-Gated Ca²⁺ Channel β₄ Subunit Creates a Uniquely Folded N-Terminal Protein Binding Domain with Cell-Specific Expression in the Cerebellar Cortex

Electrophysiological comparison of full-length β_4a and BCDE. A, Ca_v2.1 current size as a function of time after injection of no β (X), β_4a (filled symbols), or BCDE (open symbols) cRNA. Inset, RNA gel showing α1, α2/δ mixtures with increasing amounts of β₄ constructs (β₄ to α1 ratios: squares, 1:1 β₄ molar ratio relative to α1; diamonds, 4:1 ratio; circles, 12:1 ratio). B, Representative Ca_v2.1 current traces in the absence (dashed line on top of gray trace) and presence of β_4a (black traces) or BCDE (gray traces). Effects of increasing injected amounts (in nanograms) of β₄ constructs on rate of inactivation are indicated by arrows. C, Effects of increasing injected amounts (in nanograms) of β_4a (top) and BCDE (bottom) on Ca_v2.1 activation. D, Effects of increasing amounts (in nanograms) of β_4a (top) and BCDE (bottom) on Ca_v2.1 closed-state inactivation. Symbols represent mean values, and lines serve to connect data points.