Murphy G J, Hruby V J, Trivedi D, Wakelam M J, Houslay M D
Biochem J. 1987 Apr 1;243(1):39-46. doi: 10.1042/bj2430039.
Treatment of intact hepatocytes with glucagon, TH-glucagon [( 1-N-alpha-trinitrophenylhistidine, 12-homoarginine]glucagon), angiotensin or vasopressin led to a rapid time- and dose-dependent loss of the glucagon-stimulated response of the adenylate cyclase activity seen in membrane fractions isolated from these cells. Intracellular cyclic AMP concentrations were only elevated with glucagon. All ligands were capable of causing both desensitization/loss of glucagon-stimulated adenylate cyclase activity and stimulation of inositol phospholipid metabolism in the intact hepatocytes. Maximally effective doses of angiotensin precluded any further inhibition/desensitizing action when either glucagon or TH-glucagon was subsequently added to these intact cells, as has been shown previously for the phorbol ester TPA (12-O-tetradecanoylphorbol 13-acetate) [Heyworth, Wilson, Gawler & Houslay (1985) FEBS Lett. 187, 196-200]. Treatment of intact hepatocytes with these various ligands caused a selective loss of the glucagon-stimulated adenylate cyclase activity in a washed membrane fraction and did not alter the basal, GTP-, NaF- and forskolin-stimulated responses. Angiotensin failed to inhibit glucagon-stimulated adenylate cyclase activity when added directly to a washed membrane fraction from control cells. Glucagon GR2 receptor-stimulated adenylate cyclase is suggested to undergo desensitization/uncoupling through a cyclic AMP-independent process, which involves the stimulation of inositol phospholipid metabolism by glucagon acting through GR1 receptors. This action can be mimicked by other hormones which act on the liver to stimulate inositol phospholipid metabolism. As the phorbol ester TPA also mimics this process, it is proposed that protein kinase C activation plays a pivotal role in the molecular mechanism of desensitization of glucagon-stimulated adenylate cyclase. The site of the lesion in desensitization is shown to be at the level of coupling between the glucagon receptor and the stimulatory guanine nucleotide regulatory protein Gs, and it is suggested that one or both of these components may provide a target for phosphorylation by protein kinase C.
用胰高血糖素、TH-胰高血糖素[（1-N-α-三硝基苯组氨酸，12-高精氨酸）胰高血糖素]、血管紧张素或血管加压素处理完整的肝细胞，导致从这些细胞分离的膜组分中，胰高血糖素刺激的腺苷酸环化酶活性的反应迅速出现时间和剂量依赖性丧失。细胞内的环磷酸腺苷浓度仅在胰高血糖素作用下升高。所有配体都能够导致完整肝细胞中胰高血糖素刺激的腺苷酸环化酶活性的脱敏/丧失，以及刺激肌醇磷脂代谢。当随后向这些完整细胞中添加胰高血糖素或TH-胰高血糖素时，血管紧张素的最大有效剂量排除了任何进一步的抑制/脱敏作用，正如之前对佛波酯TPA（12-O-十四烷酰佛波醇13-乙酸酯）所显示的那样[海沃思、威尔逊、高勒和豪斯利（1985年）《欧洲生物化学学会联合会快报》187，196 - 200]。用这些不同的配体处理完整的肝细胞，导致在洗涤后的膜组分中胰高血糖素刺激的腺苷酸环化酶活性选择性丧失，并且不改变基础的、GTP-、NaF-和福斯可林刺激的反应。当直接添加到对照细胞的洗涤后膜组分中时，血管紧张素未能抑制胰高血糖素刺激的腺苷酸环化酶活性。胰高血糖素GR2受体刺激的腺苷酸环化酶被认为通过一个不依赖环磷酸腺苷的过程发生脱敏/解偶联，该过程涉及胰高血糖素通过GR1受体作用刺激肌醇磷脂代谢。这种作用可以被其他作用于肝脏以刺激肌醇磷脂代谢的激素模拟。由于佛波酯TPA也模拟这个过程，有人提出蛋白激酶C的激活在胰高血糖素刺激的腺苷酸环化酶脱敏的分子机制中起关键作用。脱敏损伤的部位显示在胰高血糖素受体与刺激性鸟嘌呤核苷酸调节蛋白Gs之间的偶联水平，并且有人提出这些组分中的一个或两个可能为蛋白激酶C的磷酸化提供靶点。
