Figure 1.

The effects of RGS4, PIP₃, and Ca²⁺/CaM upon single-channel K_G currents in patches from atrial myocytes. Experiments were performed on excised inside-out membrane patches in symmetrical 150 mM K⁺ solutions with 0.3 μM ACh in the pipette. Arrowheads indicate the zero current level. I/O indicates the excision of the patch from the myocyte. Compounds were applied in bath solution to the internal surface of patches for the periods indicated by the bars above the current records. (A) The effects of RGS4 and Ca²⁺/CaM on channel activity. (a) Concentration-dependent inhibitory effect of GST-RGS4 on K_G channel currents. (b) The addition of 1 μM CaM and 100 μM Ca²⁺ had no effect on the inhibition of K_G channels by 10 nM GST-RGS4. (B) The effect of PIP₃. (a) PIP₃ (1 μM) severely reduced the inhibitory effect of GST-RGS4, an effect that is reversed by Ca²⁺/CaM. (b) In PIP₃ and Ca²⁺/CaM the effect of GST-RGS4 was not inhibited. (C) The NPo of K_G channel currents recorded under different conditions (indicated below) relative to that seen in 3 μM GTP. N represents the number of K_G channels in a patch, and Po represents the open probability of each channel. Symbols and bars indicate the mean ± SEM; n = 10 for each. (D) Dose-dependent inhibition by GST-RGS4 of K_G channel currents in the absence (closed circles) or presence (open circles) of 1 μM PIP₃, and in the presence of 1 μM PIP₃ and Ca²⁺/CaM (open squares). Symbols and bars indicate the mean ± SEM, n = 6 for each. Vertical bars represent 5 pA, and horizontal bars represent 1 min.