title: Thermodynamic analysis of ligands at cholecystokinin CCK2 receptors in rat cerebral cortex.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  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
  CCK(2) receptor agonists and antagonists at rat CCK(2) receptors cannot be discriminated by thermodynamic analysis using [(3)H]-JB93182 as the radioligand.
authors.affiliation: James Black Foundation, 68 Half Moon Lane, Dulwich, London, UK. elaine.harper@kcl.ac.uk
authors.forename: E A
authors.initials: EA
authors.lastname: Harper
authors.forename: S P
authors.initials: SP
authors.lastname: Roberts
authors.forename: S B
authors.initials: SB
authors.lastname: Kalindjian
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001681:Biological Assay; D002540:Cerebral Cortex; D007211:Indoles / Q000378:metabolism; D008024:Ligands; D008297:Male; D051379:Mice; D011869:Radioligand Assay / Q000379:methods*; D019275:Radiopharmaceuticals; D051381:Rats; D017208:Rats, Wistar; D043887:Receptor, Cholecystokinin B / Q000819:agonists* / Q000037:antagonists & inhibitors*; D013696:Temperature; D013816:Thermodynamics
chemical_list: D007211:Indoles; C109753:JB93182; D008024:Ligands; D019275:Radiopharmaceuticals; D043887:Receptor, Cholecystokinin B