Figure 1.

E7K mutant presented a higher PI(4,5)P₂ sensitivity than the wild-type (WT)-TRPM4 channel. (A) In the inside-out patch configuration and after the fast rundown, diC₈-PI(4,5)P₂ (5 μM) restored TRPM4 channel activity over its initial magnitude. Vertical deflections reflect ramp- or step pulse-induced currents. (B) Representative data from two inside-out patch membranes (WT and E7K) demonstrating the dose-dependent reactivation of TRPM4 channels in response to various concentrations of diC₈-PI(4,5)P₂. (C) The degree of reactivation by diC₈-PI(4,5)P₂ (relative current) is defined as (I_[x] − I_{[post-desens]})/(I_{[20μM diC8-PIP2]} − I_{[post-desens]}), where I_[x] and I respectively denote the amplitudes of TRPM4 currents reactivated by given (‘X’ μM) and maximal (20 μM) concentrations of diC₈-PI(4,5)P₂, and I_{[post-desens]} is that of the basal TRPM4 current after desensitization to 300 μM Ca²⁺ [13]. Averaged concentration-response curves for the TRPM4 channel reactivation by diC₈-PI(4,5)P₂ are fitted by the Hill-type equation: 1/(1 + (EC₅₀/[diC₈PIP₂])ⁿ. It gives EC₅₀ values of 2.40 ± 0.23 μM and 1.44 ± 0.20 μM; Hill coefficient (n) values of 1.5 and 1.2 for WT and E7K, respectively. * p < 0.05 with ANOVA followed by Tukey’s post hoc tests (n = 5).