Figure 6.

Effects of mutations D1546K and K1543D in the EF-hand of Ca_V1.2 on sensitivity to Mg²⁺. Modulation of I_Ba through WT and mutant Ca_V1.2 channels by Mg²⁺. The fit curves are binding isotherms obtained with a global fitting procedure implemented in Igor Pro as described in the legend to Fig. 4. The apparent K_d value for inhibition by Mg_i was 0.16 mM for K1543D. The fit to the D1546K data was not significantly better than the fit to a horizontal straight line, so the horizontal line is plotted. The assumption of a common asymptote was tested by fitting the data individually using the common Hill coefficient (0.77) and comparing the individual extrapolated ordinate asymptotes. No statistically significant difference in extrapolated maximum current at Mg_i = 0 was observed, consistent with the conclusion that all mutants were expressed similarly to WT.