Phospholipase A2 and phospholipase C are activated by distinct GTP-binding proteins in response to alpha 1-adrenergic stimulation in FRTL5 thyroid cells.
In FRTL5 rat thyroid cells, norepinephrine, by interacting with alpha 1-adrenergic receptors, stimulates inositol phosphate formation, through activation of phospholipase C, and arachidonic acid release. Recent studies have shown that GTP-binding proteins couple several types of receptors to phospholipase C activation. The present study was undertaken to determine whether GTP-binding proteins couple alpha 1-adrenergic receptors to stimulation of phospholipase C activity and arachidonic acid release. When introduced into permeabilized FRTL5 cells, guanosine 5'-[gamma-thio]triphosphate (GTP[gamma-S]), which activates many GTP-binding proteins, stimulated inositol phosphate formation and arachidonic acid release. Neomycin inhibited GTP[gamma-S]-stimulated inositol phosphate formation but was without effect on GTP[gamma-S]-stimulated arachidonic acid release, suggesting that separate GTP-binding proteins mediate each process. In addition, pertussis toxin inhibited norepinephrine-stimulated arachidonic acid release but not norepinephrine-stimulated inositol phosphate formation. Norepinephrine-stimulated arachidonic acid release but not inositol phosphate formation was also inhibited by decreased extracellular calcium and by TMB-8, suggesting a role for a phospholipase A2. To confirm that arachidonic acid was released by a phospholipase A2, FRTL5 membranes were incubated with 1-acyl-2-[3H]arachidonoyl-sn-glycero-3-phosphocholine. GTP[gamma-S] slightly stimulated arachidonic acid release, whereas norepinephrine acted synergistically with GTP[gamma-S] to stimulate arachidonic acid release. The results show that phospholipase C and phospholipase A2 are activated by alpha 1-adrenergic agonists. Both phospholipases are coupled to the receptor by GTP-binding proteins. That coupled to phospholipase A2 is pertussis toxin-sensitive, whereas that coupled to phospholipase C is pertussis toxin-insensitive.
D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D002118:Calcium / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology; D004075:Diglycerides / Q000494:pharmacology; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007295:Inositol Phosphates / Q000378:metabolism; D009355:Neomycin / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D037342:Pertussis Toxin; D010740:Phospholipases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D013961:Thyroid Gland / Q000502:physiology*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D001095:Arachidonic Acids; D004075:Diglycerides; D007295:Inositol Phosphates; D011942:Receptors, Adrenergic, alpha; D010566:Virulence Factors, Bordetella; D016718:Arachidonic Acid; D037342:Pertussis Toxin; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D009355:Neomycin; D002118:Calcium; D009638:Norepinephrine