title: Both pertussis toxin-sensitive and insensitive g-proteins link melatonin receptor to inhibition of adenylate cyclase in the ovine pars tuberalis.
abstract: Bordetella pertussis toxin (islet activating protein, IAP) has been used to investigate the G-proteins involved in mediating the action of the melatonin receptor. Melatonin inhibits iorskolin-stimulated cyclic AMP production in ovine pars tuberalis (PT) cells. In cells treated with IAP for 16 h this response is attenuated in a dose-dependent manner, but not abolished. IAP catalyses the incorporation of [(32) P-ADP]ribose into a 41 kd protein present in PT membranes, but this labelling can be reduced if PT cells are preincubated with IAP for 16 h. Treatment of crude membrane preparations with IAP (20 /ig/ml) suppresses the binding of 2-[(125) l]iodomelatonin by 20%, whereas 1 mM GTP alone reduces binding by 40%, and in combination with IAP its effect is additive (60% inhibition). Therefore, these results indicate that the melatonin receptor acts via two G-proteins, one pertussis toxin-sensitive and the other pertussis toxin-insensitive.
authors.affiliation: Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen AB2 9SB, UK.
authors.forename: P J
authors.initials: PJ
authors.lastname: Morgan
authors.forename: G
authors.initials: G
authors.lastname: Davidson
authors.forename: W
authors.initials: W
authors.lastname: Lawson
authors.forename: P
authors.initials: P
authors.lastname: Barrett