Table 2.

pK_i values for a range of NOP ligands measured in CHO_INDhNOP membranes induced with 5 μM ponasterone A

Ligand Agonist	Class Peptide (P)/non-peptide (NP)	pKi
N/OFQ	P	9.93±0.08
N/OFQ–NH2	P	10.37±0.04
N/OFQ(1-13)–NH2	P	10.35±0.04
Presumed partial agonists NalBzOH	NP	7.1±0.02
[F/G]N/OFQ(1-13)–NH2	P	9.6±0.1
Ac-RYYRIK–NH2	P	9.12±0.02
Ac-RYYRWK–NH2	P	9.99±0.03
Antagonist
J-113397	NP	9.09±0.11

pK_i values were calculated using the Cheng and Prusoff equation using a K_D of 60.3 pM for [leucyl-³H]N/OFQ, measured in saturation experiments for the same induction (Table 1). Data are mean±s.e.m. (n=4).