Physicochemical modulation of agonist-induced [35s]GTPgammaS binding: implications for coexistence of multiple functional conformations of dopamine D1-like receptors.
Dopamine agonist-stimulated [35S]GTPgammaS binding to membrane G proteins was studied in select brain regions under experimental conditions that permit the activation of receptor coupling to the G proteins Gi, Gs, or Gq. Agents studied were agonists known to be effective at various dopamine receptor/effector systems and included quinelorane (D2-like/Gi), SKF38393 (D1-like/Gq, D1-like/Gs), SKF85174 (D1-like/Gs), and SKF83959 (D1-like/Gq). Dopamine and SKF38393 significantly stimulated [35S]GTPgammaS binding to normal striatal membranes by 161% and 67% above controls. Deoxycholate, which enhances agonist-induced phospholipase C (PLC) stimulation, markedly enhanced the agonistic effects of dopamine and SKF38393 to 530% and 637% above controls, respectively. The enhancing effects of deoxycholate were reversed if it was washed off the membranes before agonist addition. The thiol-reducing agent, dithiothreitol, completely abolished the effects of SKF38393 and SKF83959, whereas SKF85174 effects were augmented. Agonist responses were concentration-related, and highest efficacies were obtained in the hippocampus, thus paralleling both the brain regional distribution and agonist efficacies previously observed in phosphoinositide hydrolysis assays. These findings suggest that D1-like receptor conformations that mediate agonist stimulation of Gs/adenylylcyclase may be structurally different from those that mediate Gq/PLC activation. Although the exact mechanism of deoxycholate's effect awaits elucidation, the results are consistent with the emerging concept of functional selectivity whereby deoxycholate could create a membrane environment that facilitates the transformation of the receptor from a conformation that activates Gs/adenylylcyclase to one that favors Gq/PLC signaling.
Panchalingam
Sandra
S
Neuropharmacology Laboratory, Department of Pharmaceutical Sciences, School of Pharmacy and The Program in Neuroscience, University of Maryland, Baltimore, Maryland 21201-1075, USA.
Undie
Ashiwel S
AS
D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism*; D003840:Deoxycholic Acid / Q000494:pharmacology; D003902:Detergents / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D018491:Dopamine Agonists / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism*; D008297:Male; D011487:Protein Conformation; D051381:Rats; D017207:Rats, Sprague-Dawley; D017447:Receptors, Dopamine D1 / Q000737:chemistry* / Q000378:metabolism*
D003902:Detergents; D018491:Dopamine Agonists; D017447:Receptors, Dopamine D1; D003840:Deoxycholic Acid; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D019204:GTP-Binding Proteins; D004229:Dithiothreitol