Fig. 5.
mGluR2 occluded D2 activation of GIRK.A, In an oocyte expressing both mGluR2 and D2, 1 μm dopamine evoked a GIRK current. Subsequent application of 100 μm glutamate in the continuous presence of dopamine evoked additional GIRK current (left panel). However, after recovery, the application of 100 μmglutamate evoked a large GIRK current. Subsequent application of dopamine in the continuous presence of glutamate produced no additional current (middle panel). On washout of agonists, dopamine again evoked a GIRK response (right panel), suggesting that mGluR2 occlusion of dopamine responses reflects use of a common pool of G-proteins rather than heterologous desensitization.B, mGluR2 and D2 responses were additive when mGluR2 was not maximally activated by using low glutamate concentrations (2 μm). At left, the initial application of 1 μm dopamine evoked a GIRK current, and subsequent application of 2 μm glutamate evoked additional GIRK current, as in A, left panel. In contrast to A, middle panel, the initial application of 2 μm glutamate evoked GIRK current, yet application of dopamine evoked additional current. A andB are from two different oocytes.