Fig. 2.

IS4 charge neutralizations cause correlating changes in activation and inactivation. a Steady-state activation of Cav1.2 mutants with gradually neutralized IS4 charges. b Activation currents of I_Ba through WT and mutant channel constructs with partially neutralized S4 segments (IS4(K1Q) and IS4(K1Q/R2Q/R3Q/R4Q)). Currents were recorded by applying a 100-ms pulse from holding potential (−80 mV) with 10 mV steps (WT −30 mV − 10 mV, K1Q −20 mV − 20 mV, K1Q/R2Q/R3Q/R4Q −50 mV − −20 mV). IS4(K1Q/R2Q/R3Q/R4Q) activates at more negative voltages than IS4(K1Q/R2Q/R3Q) and WT while IS4(K1Q) activates at more positive voltages (Table 1). Charge neutralization in IS4 (K1Q/R2Q/R3Q/R4Q) notably accelerates inactivation. Compare typical current recordings of WT (upper panel) with mutants K1Q (middle panel) and quadruple mutant IS4(K1Q/R2Q/R3Q/R4Q) (lower panel). c, Correlation between potentials of half-maximal activation (V _0.5,act) and half-maximal inactivation (V _0.5,inact) of IS4 mutants (Table 1). Linear regression analysis (solid line) yielded a statistically significant linear correlation (p < 0.01) with a correlation coefficient of 0.95