Figure 12.

Trp²⁸¹ and Trp²⁸² recapitulate the PCMBS-mediated shift in apparent Ca²⁺ affinity. Complete Ca²⁺ concentration response experiments were performed to estimate EC₅₀ and Hill coefficients (h) for those constructs expressing macroscopic currents, as described in Fig. 3. (A) Plot of normalized 〈I〉 current against the corresponding Ca²⁺_i for KCa3.1 C276W (•) and C277W (□). KCa3.1 (▴) and KCa3.1+PCMBS (▵) are included for comparison. KCa3.1 C276W (n = 7), EC₅₀ = 558 ± 50 nM and h = 1.8 ± 0.1; KCa3.1 C277W (n = 6), EC₅₀ = 748 ± 54 nM and h = 1.5 ± 0.1; KCa3.1 (n = 57), EC₅₀ = 508 ± 13 nM and h = 2.0 ± 0.2; and KCa3.1+PCMBS (n = 6), EC₅₀ = 235 ± 17 nM and h = 2.5 ± 0.2. (B) Plot of normalized 〈I〉 current against the corresponding [Ca²⁺]_i for KCa3.1 L281W (■), KCa3.1 L281W+PCMBS (□), and KCa3.1 V282W (○). KCa3.1 (▴) and KCa3.1+PCMBS (▵) are included for comparison. KCa3.1 L281W (n = 12), EC₅₀ = 54 ± 6.4 nM and h = 3.3 ± 0.2; KCa3.1 L281W+PCMBS (n = 3), EC₅₀ = 43 ± 1.2 nM and h = 3.6 ± 0.5; KCa3.1 V282W (n = 12), EC₅₀ = 296 ± 14 nM and h = 1.6 ± 0.1; KCa3.1 (n = 57), EC₅₀ = 508 ± 13 nM and h = 2.0 ± 0.2; and KCa3.1+PCMBS (n = 6), EC₅₀ = 235 ± 17 nM and h = 2.5 ± 0.2. Error bars represent standard SEM. Error bars smaller than the symbols are not visible in the graph.