Fig. S6.

Related to Fig. 6. M₁ and M₂ receptors were coexpressed with GIRK2 channels, with or without SMIT1 expression. We found that the addition of M₁ receptors dramatically diminished the peak GIRK2 current induced by the shared agonist Oxo-M, suggesting depletion of PI(4,5)P₂ by M₁ receptor activation. Consistent with an enlarged pool of PI(4,5)P₂, SMIT1 delayed PI(4,5)P₂ depletion the reversed the reduction of peak GIRK2 current. (A) Representative current time courses showing that myo-inositol supplementation and SMIT1 overexpression modulated the effect of Oxo-M on GIRK2 currents. GIRK2 channels are coexpressed with M₁ and M₂ muscarinic acetylcholine receptors. I is the current amplitude induced by high concentrations of KCl, which includes ∼2 pA/pF through endogenous potassium channels. This 2 pA/pF was subtracted from I, generating I* in B. ΔI is the current amplitude induced by applying 10 μM Oxo-M, activating both M₁ and M₂ receptors. (B) Summary of the effects of SMIT1 and myo-inositol on the ratio of ΔI versus I* for GIRK2 channels coexpressed with M₁ and M₂ receptors. GIRK2 with only M₂ receptors were used as a reference (n = 5–11). Data are means ± SEM.