FIGURE 5.

CaMKII shifts I_Na availability but not activation. I_Na was measured in HEK cells expressing WT, S516A, S593A/T594A, T594A, S571A, or S593A mutant hNa_V1.5 plus GFP-δ_C-CaMKII (pipette containing 1 μm Ca²⁺ plus 1 μm CaM with or without AIP). A, representative raw I_Na and mean current-voltage relationships. Protocols for I-V (top) and steady state inactivation (SSI; bottom) for D and E are shown. B and C, voltage dependence and V₅₀ of activation were not different among groups or with/without AIP. D and E, I_Na availability was shifted to more negative V_m by δ_C-CaMKII in WT and S593A control, which was prevented by AIP. S516A, S593A/T594A, T594A, and S571A did not show this effect (n as indicated, ±S.E. (error bars); *, p < 0.05 by t test versus with AIP and two-way ANOVA but no difference among the indicated groups).