Effects of nucleotides on the binding sites for ³Hglibenclamide in rat cardiac ventricular membranes

Objective: To study the effects of nucleotides on the specific ³Hglibenclamide (Gli) binding to rat cardiac ventricular membranes.Methods: Radiolig and binding techniques including competitive or/ and kinetic assay of association and dissociation were employed to determine the modulation of ATP，ADP，UDP，AMP and adenosine (Ade) on the specific ³HGli binding to rat cardiac ventricular membranes，respectively.Results: It was observed that ³HGli bound reversibly and specifically to cardiac membranes and unlabeled Gli displaced the specific ³HGli binding completely with IC₅₀ of 195nmol/L.Under the same conditions，ATP，ADP and UDP (from 0.01 to 5mmol/L) concentration dependently inhibited ³HGli binding and the values of IC₅₀ were 1.68，0.80 and 2.08 mmol/L，respectively，whereas AMP and Ade did not inhibit the binding up to 1 mmol/L.Analysis of the kinetic experiment showed that the time of ³HGli association and dissociation in cardiac preparations conformed to first-order kinetics.The association was delayed and the dissociation kept unchanged by ATP，ADP and UDP of 1 mmol/L，respectively.Conclusion: It is suggested that ATP，ADP and UDP could change the conformation of SUR and thus regulate the specific binding of Gli in the negative allosteric manner in cardiac membranes.