Selective activation of inhibitory G-protein alpha-subunits by partial agonists of the human 5-HT1A receptor.
Plasma membranes from Chinese hamster ovary (CHO) cells transfected with the serotonin 5-HT1A receptor have been incubated with full or partial receptor agonists and the photoreactive GTP analog, 4-azidoanilido-[alpha-32P]-GTP ([32P]-AA-GTP), to characterize the resulting receptor-G-protein interactions. Subsequent solubilization and immunoprecipitation of the membranes with anti-G(i)alpha-2 or anti-G(i)alpha-3 immunoglobulins revealed that full and partial agonists produce concentration-dependent labeling of the respective G-proteins with [32P]-AA-GTP. Full agonists of the 5-HT1A receptor [serotonin 5-hydroxytryptamine (5-HT) and 8-hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT)] produced a 7-12-fold increase in the labeling of G(i)alpha-2 and G(i)alpha-3, whereas partial agonists (rauwolscine and ipsapirone) produced a smaller incorporation (2-5-fold) of [32P]-AA-GTP by the same G-proteins. The concentration of agonist producing half-maximal binding of [32P]-AA-GTP by G(i)alpha-3 [5-HT, 48 +/- 1 nM; 8-OH-DPAT, 28 +/- 1 nM; ipsapirone, 22 +/- 6 nM] compared to G(i)alpha-2 [5-HT, 124 +/- 38 nM; 8-OH-DPAT, 40 +/- 1 nM, ipsapirone, 82 +/- 7 nM] was lower with all agonists except rauwolscine, where the EC50's were similar (G(i)alpha-2, 604 +/- 145 nM; Gi alpha-3, 708 +/- 130 nM).(ABSTRACT TRUNCATED AT 250 WORDS)
Gettys
T W
TW
Department of Medicine, Medical University of South Carolina, Charleston 29425.
Fields
T A
TA
Raymond
J R
JR
D000067956:Adenylyl Cyclase Inhibitors; D000345:Affinity Labels; D000818:Animals; D001386:Azides; D016466:CHO Cells; D006224:Cricetinae; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives; D006367:HeLa Cells; D006801:Humans; D010446:Peptide Fragments / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D011233:Precipitin Tests; D011743:Pyrimidines / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D015016:Yohimbine / Q000494:pharmacology
D000067956:Adenylyl Cyclase Inhibitors; D000345:Affinity Labels; D001386:Azides; D010446:Peptide Fragments; D010761:Phosphorus Radioisotopes; D011743:Pyrimidines; D017366:Serotonin Receptor Agonists; D015016:Yohimbine; C031907:GTP gamma-4-azidoanilide; C043077:ipsapirone; D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins