Table 2. Properties of Agonist and Antagonist Radioligand Binding in Membranes from Whole Brain or Spinal Cord of Wild-Type and Gα_o Transgenic Mice.

Tissue	Genotype	[3H]DPN binding		[3H]DAMGO binding
		Total (fmol/mg protein)	MOR (fmol/mg protein)a	Bmax (fmol/mg protein)	KD (nM)
Whole brain	Wild type	366±24	218±13b	246±29	2.5±0.4
	Gαo +/−	391±38	216±3	181±16	1.9±0.5
	Gαo −/−	407±38	233±12	121±17*	3.5±1.3
Spinal cord	Wild type	161±20	95±5	84±5c	ND
	Gαo +/−	161±14	101±6	93±6c	ND

Abbreviation: ND, not determined.

^aMOR expression was evaluated as the amount of bound [³H]DPN at a maximal concentration that was displaced by the MOR-selective antagonist CTAP (300 nM).

^bIn wild-type whole brain, there is a trend for total MOR to be less than high-affinity MOR because binding was measured indirectly (see Materials and Methods).

^cIn spinal cord, B_max values were estimated using a single maximal concentration of [³H]DAMGO.

Data represent the mean±SEM (n=2–3 performed in at least duplicate). Asterisk indicates a statistical difference vs wild-type whole brain by Bonferroni's post-test (p<0.05).