FIGURE 5.

Intracellular loops of M3 muscarinic receptor specifically enhance efficiency of Gα_q-dependent activation of PLC. A, [³H]IP₃ release from [³H]PIP₂-labeled vesicles due to PLCβ3 activation by Gα_q-GDP-AlF₄⁻ was measured as a function of M3R loop concentration as described under “Experimental Procedures.” B, IP₃ release from [³H]PIP₂-labeled vesicles due to PLCβ3 activation was measured in the presence of calcium only, Gβ₁γ₂, or Gα_q-GDP-AlF₄⁻. Buffer (in which all fusion proteins were suspended) or a 300 nm concentration of GST, M3Ri2, M3Ri3Na, or M3R/H8-CT was added. C, PLCβ3 activation was measured as a function of [Gα_q-Mg-GDP-AlF₄⁻]. A representative plot is shown. D, IP₃ release from [³H]PIP₂-labeled vesicles due to activation of PLCβ3 (filled) and PLCβ2 (empty) was measured in the presence of Gα_q-GDP-AlF₄⁻. For C and D, M3Ri2, M3Ri3Na, and M3R/H8-CT were included at 200 nm. All assay results are representative of at least three independent experiments that contained internal triplicates per experimental condition. Error bars represent S.E.