Figure 1

The affinity of intracellular Mg²⁺ for WT Kir2.1 channel in symmetrical 100 mM K⁺.

(a)Sample sweeps demonstrating the inhibition of WT Kir2.1 currents in the same patch by intracellular Mg²⁺ in symmetrical 100 mM K⁺. The membrane voltage was repolarized from a holding potential of 0 mV to −100 mV for 20 ms and then stepped to test pulses between −150 and +100 mV in 10 mV increment for 150 ms. The dashed lines indicate the zero current level. (b) The relative current is defined by the ratio between the steady–state currents in Mg²⁺ and in control at each designated membrane potential and are plotted against Mg²⁺ concentration (n = 5–8). The data obtained at different membrane voltages (from −60 to +60 mV) are fitted by Eq. 1 (see Methods). (c) The Kd from part b is plotted against membrane voltage on a semi–logarithmic scale. The Kd–voltage relationship is clearly nonlinear, with the most evident change around 0 mV (the reversal potential of K⁺ ion; E_K⁺). The IR index (defined as the ratio between the Kd values at −30 and +30 mV¹³) is ~95 in this case.