Fig. 3.

MMPIP analogs exhibit lower efficacies in thallium flux assays, and the potency of MMPIP is lower than in calcium mobilization studies. A, compounds were preapplied to mGluR7a/HEK/GIRK cells before the addition of an EC₈₀ concentration of l-AP4, and thallium flux through the GIRK channel was measured. B, MMPIP concentration-response in thallium flux assays using cells expressing mGluR4, mGluR7, mGluR8, and M4 muscarinic receptor. In each case, concentration-response curves were applied to cells before an appropriate EC₈₀ concentration of either l-AP4 (mGluR4, 7, and 8) or acetylcholine (M4). The potency of MMPIP in these experiments was 2.0 ± 0.2 μM. C, corrected concentration-response curve for MMPIP after normalizing for nonspecific effects of the compound on M4/GIRK cells. Methods for this correction are described under Materials and Methods. Revised potency of MMPIP, 717 ± 89 nM. Values represent mean ± S.E.M. and are an n of three experiments performed in quadruplicate.