TABLE 3

Parameters of induced [³⁵S]GTPγS binding to G_i, G_s, and G_q subtypes of G proteins

Induced binding to individual subtypes of G proteins in membranes from CHO cells expressing M₁ or M₂ receptors, respectively, was detected by scintillation proximity assay. E_MAX is expressed as percentage increase above basal binding, and concentrations of agonist producing EC₅₀ are expressed as negative logarithms of [³⁵S]GTPγS binding to G_i, G_s, and G_q G proteins, respectively. Data are means ± S.E.M. from three to four independent experiments performed in quadruplicates.

	M₁		M₂
	pEC₅₀	E_MAX	pEC₅₀	E_MAX
		% above basal		% above basal
Without preincubation
Carbachol
G_i	5.33 ± 0.06	96 ± 7	6.11 ± 0.05	248 ± 11
G_s	5.44 ± 0.05	92 ± 8	5.29 ± 0.06	79 ± 6
G_q	5.94 ± 0.06	289 ± 11	5.38 ± 0.05	55 ± 5
Xanomeline
G_i	6.28 ± 0.06	68 ± 6	7.54 ± 0.05	59 ± 6
G_s	6.37 ± 0.04	77 ± 7	n.e.	n.e.
G_q	8.11 ± 0.04	283 ± 9	n.e.	n.e.
With 60-min preincubation
Carbachol
G_i	5.37 ± 0.05	103 ± 8	6.13 ± 0.05	255 ± 12
G_s	5.46 ± 0.04	100 ± 7	5.31 ± 0.06	82 ± 6
G_q	6.01 ± 0.04	309 ± 12	5.42 ± 0.04	57 ± 6
Xanomeline
G_i	6.30 ± 0.05	72 ± 7	7.67 ± 0.06^*	121 ± 7^*
G_s	6.39 ± 0.05	81 ± 7	5.82 ± 0.04	38 ± 4
G_q	8.16 ± 0.03	294 ± 10	6.19 ± 0.04	49 ± 4
With 60-min preincubation followed by washing Xanomeline
G_i	4.23 ± 0.05^†	49 ± 4^†	5.96 ± 0.06^†	95 ± 6^†
G_s	4.43 ± 0.05^†	53 ± 4^†	4.09 ± 0.05^†	28 ± 5
G_q	5.98 ± 0.04^†	260 ± 10	4.36 ± 0.05^†	41 ± 5

n.e., no effect.
↵* Significantly different from no preincubation (P < 0.05; ANOVA followed by Tukey-Kramer post-test).
↵† Significantly different from 60-min preincubation (P < 0.05; ANOVA followed by Tukey-Kramer post-test).