title: Somatostatin receptors (sst2) are coupled to Go and modulate GTPase activity in the rabbit retina.
abstract: The role of somatostatin and its mechanism of action in the retina remains an important target for investigation. Biochemical and pharmacological studies were engaged to characterize the somatostatin receptors in the rabbit retina, and their coupling to G-proteins. The ability of selective ligands to inhibit [125I]Tyr11-somatostatin-14 binding to rabbit retinal membranes was examined. The sst2 analogues SMS201-995, MK678, and BIM23014, displayed IC50 values of 0.28 +/- 0.12, 0.04 +/- 0.01 and 1.57 +/- 0.39 nm, respectively. The sst1 analogue CH275 moderately displaced the [125I]Tyr11-somatostatin-14 binding, while selective analogues for sst3, sst4 and sst5 had minimal effect. Immunoblotting and/or immunohistochemistry studies revealed the presence of the pertussis toxin sensitive Gi1/2, and Go proteins, as well as Gs. Somatostatin-14 and MK678 stimulated GTPase activity in a concentration-dependent manner with EC50 values of 42.8 +/- 16.8 and 70.0 +/- 16.5 nm, respectively, thus supporting the functional coupling between the receptor and the G-proteins. CH275 stimulated the GTPase activity moderately, in agreement with its binding profile. The antisera raised against Goalpha and Gi1/2alpha inhibited the somatostatin-induced high-affinity GTPase activity, but only anti-Goalpha inhibited the MK678 stimulation of the enzyme. These results suggest that somatostatin mediates its actions in the rabbit retina by interacting mainly with sst2 receptors that couple to Goalpha.
authors.affiliation: Laboratory of Pharmacology, Department of Basic Science, Faculty of Medicine, University of Crete, Heraklion, Crete 71110, Greece.
authors.forename: Anna
authors.initials: A
authors.lastname: Vasilaki
authors.forename: Zafiroula
authors.initials: Z
authors.lastname: Georgoussi
authors.forename: Kyriaki
authors.initials: K
authors.lastname: Thermos
mesh_terms: D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D015153:Blotting, Western; D002462:Cell Membrane / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000037:antagonists & inhibitors; D020962:Heterotrimeric GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007106:Immune Sera / Q000494:pharmacology; D008024:Ligands; D008297:Male; D010456:Peptides, Cyclic / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors; D011817:Rabbits; D011869:Radioligand Assay; D017481:Receptors, Somatostatin / Q000378:metabolism*; D012160:Retina / Q000737:chemistry / Q000378:metabolism*; D013004:Somatostatin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology
chemical_list: C110576:CH 275; D007106:Immune Sera; D008024:Ligands; D010456:Peptides, Cyclic; D011518:Proto-Oncogene Proteins; D017481:Receptors, Somatostatin; C060347:lanreotide; D013004:Somatostatin; C040968:seglitide; D020558:GTP Phosphohydrolases; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020962:Heterotrimeric GTP-Binding Proteins