Harper EA, Roberts SP, Kalindjian SB. Thermodynamic analysis of ligands at cholecystokinin CCK2 receptors in rat cerebral cortex.
Br J Pharmacol 2007;
151:1352-67. [PMID:
17592503 PMCID:
PMC2189820 DOI:
10.1038/sj.bjp.0707355]
[Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2007] [Revised: 05/01/2007] [Accepted: 05/22/2007] [Indexed: 11/09/2022] Open
Abstract
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 CCK(2) receptors in rat cerebral cortex.
EXPERIMENTAL APPROACH
The pK(L) of [(3)H]-JB93182 in rat cerebral cortex membranes was determined at 4, 12, 21 and 37 degrees C in 50 mM Tris-HCl buffer (buffer B pH 6.96; containing 0.089 mM bacitracin). pK(I) values of ligands of diverse chemical structure and with differing intrinsic activity (alpha), as defined by the lumen-perfused rat and mouse stomach bioassays, were determined in buffer B at 4, 12, 21 and 37 degrees C.
KEY RESULTS
[(3)H]-JB93182 labelled a homogeneous population of receptors in rat cerebral cortex at 4, 12, 21 and 37 degrees C and the pK(L) and B(max) were not altered by incubation temperature. [(3)H]-JB93182 binding reached equilibrium after 10, 50, 90 and 220 min at 37, 21, 12 and 4 degrees C, respectively. pK(I) values for R-L-365,260, R-L-740,093, YM220, PD134,308 and JB95008 were higher at 4 degrees C than at 37 degrees C. There was no effect of temperature on pK(I) values for pentagastrin, CCK-8S, S-L-365,260, YM022, PD140,376 and JB93242.
CONCLUSIONS AND IMPLICATIONS
CCK(2) receptor agonists and antagonists at rat CCK(2) receptors cannot be discriminated by thermodynamic analysis using [(3)H]-JB93182 as the radioligand.
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