Fig. 3. CaV1.3α1 channels open at relatively hyperpolarized voltages independent of several factors that potentially affect the voltage dependence of activation. Shown are comparisons of normalized, averaged peak current–voltage plots of CaV1.3α1 coexpressed with CaVβ1b (●), CaVβ2a (○), CaVβ3(▪), or CaVβ4 (■) subunits (A); with (●) or without (○) exon 32, which encodes a 15-amino acid sequence, PSDSENIPLPTATPG, in domain IVS3–IVS4 coexpressed with CaVβ1b(B); with (●) or without (○) exon 11, which encodes a 20-amino acid sequence, CWWKRRGAAKTGPSGCRRWG, in loop I–II coexpressed with CaVβ1b(C); and with exon 42 (●) or exon 42a (○) coexpressed with CaVβ1b(D), Ca channel currents were recorded with 5 mm barium as the charge carrier. Maximum, peak current amplitudes induced by coexpressing Cav1.3α1with different CaVβ subunits were −1.3 ± 0.1 μA (n = 7; CaVβ1b), −2.8 ± 0.2 μA (n = 8; CaVβ2a), −1.0 ± 0.1 μA (n = 7; CaVβ3), and −1.0 ± 0.5 μA (n = 4; CaVβ4). Cav1.3α1 alone induced currents with amplitudes of −0.43 ± 0.05 μA (n = 6). Average V1/2 values were: A, −33.0 ± 1.0 mV (n = 7; CaVβ1b), −32.1 ± 0.8 mV (n = 8; CaVβ2a), −28.4 ± 0.5 mV (n = 7; CaVβ3), and −30.0 ± 1.0 mV (n = 4; CaVβ4);B, −35.7 ± 0.5 mV (n = 8; Δexon 32) and −31.7 ± 0.7 mV (n = 5; +exon 32); C, −36.1 ± 1.6 mV (n = 8; Δexon 11) and −35.3 ± 0.6 mV (n = 5; +exon 11); and D, −33.9 ± 1.5 mV (n = 3; +exon42) and −32.9 ± 0.4 mV (n = 5; +exon 42a). Values are mean ± SE.