| Abstrakt: |
Background and purpose:Several studies using radioligand binding assays, have shown that measurement of thermodynamic parameters can allow discrimination of agonists and antagonists (Weiland et al., 1979; Borea et al., 1996a). Here we investigate whether agonists and antagonists can be thermodynamically discriminated at CCK2 receptors in rat cerebral cortex.Experimental approach:The pKL of [3H]-JB93182 in rat cerebral cortex membranes was determined at 4, 12, 21 and 37°C in 50 mM Tris-HCl buffer (buffer B pH 6.96; containing 0.089 mM bacitracin). pKI values of ligands of diverse chemical structure and with differing intrinsic activity (α), as defined by the lumen-perfused rat and mouse stomach bioassays, were determined in buffer B at 4, 12, 21 and 37°C.Key results:[3H]-JB93182 labelled a homogeneous population of receptors in rat cerebral cortex at 4, 12, 21 and 37°C and the pKL and Bmax were not altered by incubation temperature. [3H]-JB93182 binding reached equilibrium after 10, 50, 90 and 220 min at 37, 21, 12 and 4°C, respectively. pKI values for R-L-365,260, R-L-740,093, YM220, PD134,308 and JB95008 were higher at 4°C than at 37°C. There was no effect of temperature on pKI values for pentagastrin, CCK-8S, S-L-365,260, YM022, PD140,376 and JB93242.Conclusions and implications:CCK2 receptor agonists and antagonists at rat CCK2 receptors cannot be discriminated by thermodynamic analysis using [3H]-JB93182 as the radioligand.British Journal of Pharmacology (2007) 151, 1352–1367; doi:10.1038/sj.bjp.0707355; published online 25 June 2007 [ABSTRACT FROM AUTHOR] |
