Table 1.

Agonist potencies of L-α-amino acids at mGPRC6A transiently co-expressed with Gα_qG66D in tsA cells

L-α-amino acid	EC50 (μM)	pEC50±s.e.m.	N	Concentration of L-α-amino acid (mean±s.d.) in mouse plasmaa (μM)
L-Orn	63.6	4.20±0.001	3	86±20
L-Lys	135	3.97±0.18	4	366±55
L-Arg	284	3.58±0.08b	6	137±22
L-Cys	356c	3.46±0.09b	3	Not determined
L-Ala	486	3.41±0.18b,d	4	431±85
Gly	538e	3.30±0.09b,f	4	340±54
L-Ser	1160g	2.94±0.03b,d,f	3	181±25

The IP turnover assay was used to determine the EC₅₀ values of various amino acids at mGPRC6A. The pEC₅₀ values of all the listed amino acids were compared to determine statistically significant differences (P<0.05; ANOVA followed by Tukey's test).

^aTaken from Komarov and Reddy (1998).

^bSignificantly different from L-Orn.

^cL-Cys displayed a small but significant effect on mock-transfected cells at high concentrations (⩾1 mM). The EC₅₀ value might thus be overestimated.

^dSignificantly different from L-Lys.

^eGly displayed partial agonism with a maximal response of 49±9% (mean±s.e.m.) relative to the maximal activation of mGPRC6A obtained by stimulation with 10 mM L-Arg.

^fSignificantly different from L-Arg.

^gOwing to low potency, L-Ser was tested at concentrations eliciting sub-maximal effect. Assuming full agonism, concentration–response curves for this compound were fitted using the maximal response to L-Arg (10 mM), which was always included as control.