Burch R M, Luini A, Axelrod J
Proc Natl Acad Sci U S A. 1986 Oct;83(19):7201-5. doi: 10.1073/pnas.83.19.7201.
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.
在FRTL5大鼠甲状腺细胞中，去甲肾上腺素通过与α1 - 肾上腺素能受体相互作用，激活磷脂酶C来刺激肌醇磷酸形成，并促进花生四烯酸释放。最近的研究表明，GTP结合蛋白可将几种类型的受体与磷脂酶C的激活偶联起来。本研究旨在确定GTP结合蛋白是否能将α1 - 肾上腺素能受体与磷脂酶C活性的刺激以及花生四烯酸释放偶联起来。当将能激活许多GTP结合蛋白的鸟苷5'-[γ-硫代]三磷酸（GTP[γ-S]）导入通透的FRTL5细胞时，可刺激肌醇磷酸形成和花生四烯酸释放。新霉素抑制GTP[γ-S]刺激的肌醇磷酸形成，但对GTP[γ-S]刺激的花生四烯酸释放没有影响，这表明不同的GTP结合蛋白介导每个过程。此外，百日咳毒素抑制去甲肾上腺素刺激的花生四烯酸释放，但不抑制去甲肾上腺素刺激的肌醇磷酸形成。细胞外钙浓度降低和TMB - 8也抑制去甲肾上腺素刺激的花生四烯酸释放，但不抑制肌醇磷酸形成，提示磷脂酶A2发挥了作用。为证实花生四烯酸是由磷脂酶A2释放的，将FRTL5细胞膜与1-酰基-2-[3H]花生四烯酰-sn-甘油-3-磷酸胆碱一起孵育。GTP[γ-S]轻微刺激花生四烯酸释放，而去甲肾上腺素与GTP[γ-S]协同作用刺激花生四烯酸释放。结果表明，磷脂酶C和磷脂酶A2可被α1 - 肾上腺素能激动剂激活。两种磷脂酶均通过GTP结合蛋白与受体偶联。与磷脂酶A2偶联的对百日咳毒素敏感，而与磷脂酶C偶联的对百日咳毒素不敏感。
