Fig. 2.

The potential impact of alternative splicing of Ca_V channels on the voltage range over which each channel subtype can operate. Boltzmann activation curves are plotted using V_1/2 and k values from the literature from recordings using 1–2 mM calcium as charge carrier, except for data for Ca_V1.1 obtained from recordings using 10 mM calcium. A, Ca_V1.1 (V_1/2 =6.2 mV, k=5.3 mV; [121]), Ca_V1.2 (V_1/2 = −17 mV, k=8 mV; [122]), Ca_V1.3 (V_1/2 = −36 mV, k=8 mV; [123,124]), Ca_V2.2 (V_1/2 = −0.1 mV, k=7.5 mV; [125]), and Ca_V3.1 (Ca_V3.1, V_1/2 = −46 mV, k=4.11; [126]). B, Alternative splicing of exons can modify voltage-dependence of activation and this will increase the operating voltage range for each Ca_V channel family. Approximate locations of regions encoded by alternatively spliced exons that influence the voltage-dependence of channel activation are shown. Ca_V2.2 data are from [125]; Ca_V1.1 data are from [64]; and Ca_V3.1 data are from [127]. Ca_V1.2 [128] and Ca_V1.3 [67,129] isoforms that have different activation properties were compared using 11 mM barium as charge carrier, this will shift the voltage-dependence of activation relative to recordings with 2 mM Ca. For comparison with other data, we illustrate an approximate operating range for Ca_V1.2 and Ca_V1.3 (dotted lines) based on the different V_1/2 values from [67,128,129] but with reference to the activation curves shown in A obtained with 2 mM Ca.