Fig. 3.

Heterologous expression of sponge inward-rectifier potassium (Kir) channels. Strongly rectifying currents in 5 mmol l^–1 external K⁺ (KMES) recorded from (A) AmqKirA using 2 s voltage steps from– 150 to +100 mV in +20 mV increments from a holding potential –50 mV and (B) AmqKirB using a voltage ramp from a holding potential of –50 mV. Current–voltage plots for AmqKirB taken at 10 (#1), 30 (#2), 60 (#3) and 90 (#4) mins. The inset shows, in the same cell, the time-dependent change in the normalized current at –140 mV (until the recording ended). (C) Effect of increasing external K⁺ on AmqKirA currents. Solutions of 2, 5, 10, 25 and 50 mmol l^–1 KMES were used. The inset is a semi-log plot of the reversal potential versus external K⁺ concentration for AmqKirA (N=6–28 per concentration, means± s.e.m.). The fitted line has a slope of 49 mV. (D) Representative AmqKirA current–voltage relationships recorded in 5 mmol l^–1 K⁺, 100 mmol l^–1 NMDG, and 100 mmol l^–1 Na (all used as MES salts) showing no Na or NMDG permeability. The inset shows results of the test of Na (0.03–1 mmol l^–1 NaCl) block of 5 mmol l^–1 KMES currents (N=5, means ± s.e.m.).