Figure 5.

MgATP activation of Q_Na in 20 mM Na⁺_i, with 125 mM Na⁺_o (pH 7.6). (A) MgATP-induced current (current in ATP minus current without ATP) elicited by voltage pulses from V_h = −50 mV to −160 mV or +40 mV. (B) Q_OFF-V curve for the patch in (A). Continuous lines represent global fits using the Boltzmann function (Eq. 2) with a shared slope factor kT/ez_q = 43 mV, Q_tot = 81.3 fC, V_1/2= −35 mV at 1 μM MgATP, and Q_tot = 120 fC, V_1/2 = −41 mV at 4 mM MgATP. (C) Average Q_OFF-V curves from five patches in which different [MgATP] were applied, normalized to Q_tot at 4 mM MgATP. Lines represent fits of Eq. 2 to the average data; the best fit V_1/2 values were −7.2 ± 9.0, −42 ± 4.7, −38 ± 5.2, −50 ± 5.2, and −38 ± 4.5 mV for 0.2 μM, 0.5 μM, 1 μM, 10 μM, and 4 mM ATP, respectively. No clear change in slope factor with [ATP] was observed in individual experiments; therefore, the slope factor was shared in the global fit; kT/ez_q = 43 ± 3 mV. (D) Q_tot as a function of [MgATP]. Continuous lines represent fits using Eq. 1 (n_H = 1) to the whole data set from five patches with K_0.5,ATP = 0.43 ± 0.03 μM. To see this figure in color, go online.