Fig. 9.

In contrast to effects on calcium mobilization, histamine has no effect on the activity of mGlu4 PAMs in adenylate cyclase assays in cells expressing both mGlu₄ and H₁ receptors. Increasing concentration of mGlu₄ PAMs (PHCCC, 4PAM-2, ADX88178 or VU0155041, A-D, respectively) were co-diluted with 1 µM glutamate and incubated with mGlu₄/H₁/CHO-K1 cells either alone or together with 300 nM histamine. Intracellular cAMP concentration was measured as described and then normalized to either 20 µM forskolin response or 20 µM forskolin + 300 nM histamine, respectively. Potencies in the absence or presence of 300 nM histamine were: PHCCC, 2.5 ± 0.6 µM vs. 1.8 ± 0.4 µM (p = 0.40; unpaired t-test); 4PAM-2, 55.5 ± 12.6 nM v.s 66.1 ± 8.6 nM (p = 0.53; unpaired t-test); ADX88178, 11.7 ± 2.0 nM vs. 16.0 ± 4.3 nM (p = 0.42; unpaired t-test); and VU0155041, 287.3 ± 23.1 nM vs. 360.0 ± 38.8 nM (p = 0.18; unpaired t-test). Maximal inhibition values in the absence or presence of 300 nM histamine were: PHCCC, 85.3 ± 3.4% vs. 82.0 ± 2.7% (p = 0.49; unpaired t-test); 4PAM-2, 89.0 ± 1.2 nM vs. 89.4 ± 0.6% (p = 0.77; unpaired t-test); ADX88178, 90.4 ± 1.5% vs. 91.1 ± 0.6% (p = 0.70; unpaired t-test); and VU0155041, 89.5 ± 0.4% vs. 90.0 ± 0.1% (p = 0.85; unpaired t-test). Data shown were performed in triplicate; Mean ± SEM. Statistical analysis was performed using GraphPad Prism (La Jolla, CA).