TABLE 2.

Summary of operational model parameters for positive allosteric modulation of glutamate-mediated intracellular Ca²⁺ mobilization in HEK cells expressing either low or high levels of mGlu₅

Interactions between glutamate and allosteric modulators were quantified by using eq. 2 (for α = 1), eq. 3 (for τ_B = 0), or eq. 4 (when αβ was determined); glutamate affinity was held constant at a previously reported value (logK_A = −6.155) (Mutel et al., 2000). The presence of allosteric modulators did not affect estimates of glutamate coupling efficiency (logτ_A), transduction coefficient (n), maximal system response (E_m), or basal response levels; the assumption of α = 1 also had no effect on these estimates (one-way analysis of variance) (Supplemental Table 1). In the low-level mGlu₅-expressing cell line, with αβ being determined, logτ_A = 0.75 ± 0.03, n = 2.54 ± 0.12, E_m = 102.5 ± 1.0, and basal = 1.0 ± 0.17; with α = 1, logτ_A = 0.80 ± 0.02, n = 2.66 ± 0.13, E_m = 103.5 ± 1.07, and basal = 1.15 ± 0.19. In the high-level mGlu₅-expressing cell line, logτ_A = 0.37 ± 0.02, n = 2.84 ± 0.16, E_m = 118.3 ± 2.3, and basal = 0.81 ± 0.23. Data represent the mean ± S.E.M. from at least three independent determinations.

	CDPPB	VU29	CPPHA	VU0357121	VU0364289	VU0092273	VU0360172	VU0405398	VU0415051	VU0405386
Low-level mGlu5, determining αβ
pKB	6.31 ± 0.10	6.20 ± 0.09	6.03 ± 0.10	6.46 ± 0.09	5.18 ± 0.13	6.45 ± 0.11	6.98 ± 0.05	7.30 ± 0.24	7.45 ± 0.24	8.17 ± 0.24
logαβ	0.78 ± 0.16	0.81 ± 0.08	0.65 ± 0.09	0.42 ± 0.05	0.97 ± 0.08	0.49 ± 0.04	0.51 ± 0.02	0.33 ± 0.04	0.36 ± 0.06	0.60 ± 0.11
logτB	−0.42 ± 0.23	−0.67 ± 0.06	N.A.	N.A.	N.A.	N.A.	N.A.	N.A.	N.A.	N.A.
Low-level mGlu5, assuming α = 1
pKB	6.38 ± 0.10	6.23 ± 0.09	6.06 ± 0.10	6.48 ± 0.17	5.22 ± 0.16	6.46 ± 0.12	7.00 ± 0.05	7.29 ± 0.26	7.46 ± 0.20	8.18 ± 0.28
logβ	0.66 ± 0.15	0.71 ± 0.08	0.56 ± 0.07	0.37 ± 0.05	0.90 ± 0.09	0.44 ± 0.05	0.47 ± 0.02	0.30 ± 0.04	0.30 ± 0.05	0.54 ± 0.07
logτB	−0.32 ± 0.15	−0.64 ± 0.07	N.A.	N.A.	N.A.	N.A.	N.A.	N.A.	N.A.	N.A.
High-level mGlu5, assuming α = 1
pKB	6.99 ± 0.04	6.59 ± 0.13	5.55 ± 0.14	6.00 ± 0.15	5.83 ± 0.20	6.68 ± 0.06	7.07 ± 0.14	7.29 ± 0.20	8.02 ± 0.25	8.00 ± 0.29
logβ	0.29 ± 0.05	0.54 ± 0.13	0.58 ± 0.07	0.92 ± 0.01	0.78 ± 0.05	0.77 ± 0.11	0.88 ± 0.15	0.87 ± 0.06*	0.74 ± 0.19	1.10 ± 0.16*
logτB	0.00 ± 0.01	−0.05 ± 0.06	−0.14 ± 0.15	N.A.	−0.38 ± 0.03	−0.23 ± 0.04	−0.13 ± 0.07	−0.69 ± 0.15	−0.19 ± 0.11	−0.14 ± 0.03

pK_B, negative logarithm of the allosteric modulator equilibrium dissociation constant; logαβ, logarithm of the composite cooperativity factor, αβ, which reflects both affinity and efficacy modulation, as quantified with eq. 4; logτ_B, logarithm of the coupling efficiency of the allosteric modulator; logβ, logarithm of the efficacy cooperativity factor, β, as quantified with either eq. 2 or 3 as appropriate; N.A., not applicable because of lack of appreciable agonism by the allosteric modulator.

^* Significantly different (P < 0.05) from the value for the modulator determined in low-level mGlu₅-expressing HEK293A cells for Ca²⁺ mobilization, with one-way analysis of variance and Tukey's post hoc test.