Figure 4.

Arg-Lys-Arg triad and gating is realized within one subunit. (A) (Upper) Cartoon illustrating the coexpression experiment (see text) designed to test for formation of the Arg-Lys-Arg triad via intersubunit interaction between Arg-41, Lys-80 [in K_ir1.1(R311Q, N171D)], and Arg-311 [in K_ir1.1(K80M)]. (Lower) Intersubunit interaction in a heteromultimeric complex assembled from three K_ir1.1(K80M) subunits and one K_ir1.1(R311Q, N171D) subunit. (B) Histograms illustrating current amplitudes (at −80 mV; Left), relative conductance at pH 8.4 in the presence of 100 μM SPM (at 50 mV; Center), and relative conductance at pH 6.0 in the absence of SPM (Right) observed with homomeric K_ir1.1(K80M) and channels forming on coexpression of K_ir1.1(K80M) and K_ir1.1(R311Q, N171D); all values are mean ± SD of 16–21 experiments (for the amplitudes) or of 8–11 experiments (for the conductances); relative conductance is normalization of conductance with respect to that observed in the absence of SPM or at a pH_i of 9.6. All coexpression experiments were done with an mRNA ratio of 1:10 (K80M: R311Q,N171D or K80M:N171D); note that all channels formed in the K80M:N171D coexpression were blocked by 100 μM SPM at 50 mV.