Characterization of human recombinant somatostatin sst5 receptors mediating activation of phosphoinositide metabolism.
1. We have functionally characterized the human recombinant somatostatin (SRIF) sst5 receptor in Chinese hamster ovary-K1 (CHOsst5) cells by measuring total [3H]-inositol phosphate ([3H]-InsPx) accumulation, in the presence of 10 mM LiCl, in cells labelled with [3H]-myo-inositol. 2. In CHOsst5 cells, SRIF, SRIF-28 and the cyclic hexapeptide, L-362,855, produced time- and concentration-related increases in [3H]-InsPx accumulation, with similar potency (pEC50 values of 6.5, 6.8 and 7.2, respectively). L-362,855 behaved as a partial agonist, producing approximately 30% of the SRIF maximum response. The other peptide analogues of SRIF, BIM-23027 and BIM-23056, were inactive as agonists. 3. Increasing concentrations of L-362,855 increased [3H]-InsPx accumulation and simultaneously produced rightward shifts of SRIF concentration-effect curves, with an estimated pKp value of 7.6, confirming that it was acting as a partial agonist. 4. BIM-23056, but not BIM-23027, potently antagonized SRIF-induced [3H]-InsPx accumulation, with an estimated pKB value of 7.4. BIM-23056 did not antagonize [3H]-InsPx accumulation induced by uridine 5'-triphosphate (UTP). 5. SRIF- but not UTP-induced [3H]-InsPx accumulation was inhibited by increasing concentrations of pertussis toxin (0.01-100 ng ml-1), indicating the involvement of pertussis toxin-sensitive G-proteins. 6. These findings show that the human recombinant sst5 receptor, when stably expressed in CHO-K1 cells, is able to mediate activation of phosphoinositide metabolism in a pertussis toxin-sensitive manner. In this system L-362,855 behaved as a partial agonist while BIM-23056 was a specific antagonist. These agents should provide useful tools for functionally characterizing endogenous SRIF receptors.
Wilkinson
G F
GF
Glaxo Institute of Applied Pharmacology, Department of Pharmacology, University of Cambridge.
Feniuk
W
W
Humphrey
P P
PP
D000818:Animals; D016466:CHO Cells / Q000166:cytology / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D019204:GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D007294:Inositol / Q000737:chemistry; D007553:Isotope Labeling; D018021:Lithium Chloride / Q000737:chemistry; D009842:Oligopeptides / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D037342:Pertussis Toxin; D010716:Phosphatidylinositols / Q000378:metabolism*; D017481:Receptors, Somatostatin / Q000819:agonists / Q000096:biosynthesis* / Q000378:metabolism; D011994:Recombinant Proteins / Q000819:agonists / Q000096:biosynthesis / Q000378:metabolism; D013004:Somatostatin / Q000031:analogs & derivatives / Q000494:pharmacology; D014316:Tritium; D014544:Uridine Triphosphate / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000633:toxicity
C091738:BIM 23027; C091737:BIM 23056; C091739:L 362855; D009842:Oligopeptides; D010456:Peptides, Cyclic; D010716:Phosphatidylinositols; D017481:Receptors, Somatostatin; D011994:Recombinant Proteins; D010566:Virulence Factors, Bordetella; D014316:Tritium; D007294:Inositol; D013004:Somatostatin; C020948:somatostatin, Trp(8)-Cys(14)-; C094573:somatostatin receptor 5; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D018021:Lithium Chloride; D014544:Uridine Triphosphate