FIGURE 6.

The mutations Y1657H/K1662M in the Ca_V1.2 IQ motif eliminate calcium-dependent inactivation. A, representative whole cell currents in ts-A201 cells expressing either wild-type Ca_V1.2 or Ca_V1.2[H1657Y/K1662M], elicited by depolarization to +20 mV in either 10 mm Ca²⁺ or 10 mm Ba²⁺. For both wild-type and mutant, the Ca²⁺ current has been scaled ∼2.5 times. The scale bar, which applies to the Ba²⁺ currents, represents 1000 or 500 pA (Ca_V1.2 and Ca_V1.2 mutant, respectively). B, normalized peak I-V relationships demonstrate that Ba²⁺ caused a similar shift of activation for wild-type and mutant channels. Average peak calcium and barium current densities (mean ± S.E.) for Ca_V1.2 were 32.9 ± 8.2 and 78.5 ± 16.0 pA/pF, respectively, and for Ca_V1.2[Y1657H/K1662M] were 53.2 ± 11.3 and 76.9 ± 13.7 pA/pF. C, ratio of current-50-ms-after-the-peak-inward-current to the peak-inward-current (R₅₀) plotted as a function of test potential. For B and C, the symbols are as defined in A and the error bars represent ±S.E.