Phospholipase A2 and Phospholipase C are Activated by Distinct GTP-Binding Proteins in Response to α 1-adrenergic Stimulation in FRTL5 Thyroid Cells

• Published in: Proceedings of the National Academy of Sciences - PNAS 1986-10, Vol.83 (19), p.7201-7205
• Main Authors: Burch, Ronald M., Luini, Alberto, Axelrod, Julius
• Format: Article
• Language: English
• Subjects: Animals; Arachidonic Acid; Arachidonic Acids - metabolism; Biochemistry; Calcium; Calcium - physiology; Cell Line; Cell Membrane - enzymology; Cell membranes; Diglycerides; Diglycerides - pharmacology; Enzyme Activation; GTP-Binding Proteins - antagonists & inhibitors; GTP-Binding Proteins - metabolism; Inositol phosphates; Inositol Phosphates - metabolism; Neomycin - pharmacology; Norepinephrine; Norepinephrine - pharmacology; Pertussis Toxin; Phosphatidic acids; Phospholipases - metabolism; Phospholipases A - metabolism; Phospholipases A2; Rats; Receptors; Receptors, Adrenergic, alpha - physiology; Thyroid Gland - physiology; Toxins; Type C Phospholipases - antagonists & inhibitors; Type C Phospholipases - metabolism; Virulence Factors, Bordetella - pharmacology; Whooping cough
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.83.19.7201

In FRTL5 rat thyroid cells, norepinephrine, by interacting with α 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 α 1-adrenergic receptors to stimulation of phospholipase C activity and arachidonic acid release. When introduced into permeabilized FRTL5 cells, guanosine 5′-[γ -thio]triphosphate (GTP[γ -S]), which activates many GTP-binding proteins, stimulated inositol phosphate formation and arachidonic acid release. Neomycin inhibited GTP[γ -S]-stimulated inositol phosphate formation but was without effect on GTP[γ -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[γ -S] slightly stimulated arachidonic acid release, whereas norepinephrine acted synergistically with GTP[γ -S] to stimulate arachidonic acid release. The results show that phospholipase C and phospholipase A2 are activated by α 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.