Büscher R, Erdbrügger W, Philipp T, Brodde O E, Michel M C
Department of Medicine, University of Essen, Germany.
Naunyn Schmiedebergs Arch Pharmacol. 1994 Dec;350(6):592-8. doi: 10.1007/BF00169362.
We have compared the coupling mechanisms of rat renal alpha 1A- and alpha 1B-like adrenoceptors to inositol phosphate formation. The experiments were performed in parallel in native renal tissue preparations and in those where alpha 1B-adrenoceptors had been inactivated by treatment with 10 mumol/l chloroethylclonidine for 30 min at 37 degrees C; renal slices were used in most experiments but isolated renal cells were also used in some cases. The Ca2+ chelating agent, EGTA (5 mmol/l), reduced noradrenaline-stimulated inositol phosphate formation in native but enhanced it in chloroethylclonidine-treated renal slices. The inhibitory effect of EGTA was not mimicked by 100 nmol/l nifedipine. Inactivation of 87% of cellular Gi by 16-20 h treatment with 500 ng/ml pertussis toxin did not significantly affect noradrenaline-stimulated inositol phosphate formation in isolated renal cells but abolished the inhibitory effect of chloroethylclonidine. The adenylate cyclase activator, forskolin (20 mumol/l), inhibited noradrenaline-stimulated inositol phosphate formation in native and chloroethylclonidine-treated slices, and the inhibitory effects of chloroethylclonidine treatment and forskolin were additive. We conclude that in rat kidney inositol phosphate formation via alpha 1B-like adrenoceptors may involve the influx of extracellular Ca2+ and a pertussis toxin-sensitive G-protein but is insensitive to inhibition by forskolin. In contrast alpha 1A-like adrenoceptor-mediated inositol phosphate formation does not require the presence of extracellular Ca2+ or of Gi and is sensitive to inhibition by forskolin. In comparison to published data from other model systems we further conclude that the signaling mechanisms of alpha 1-adrenoceptor subtypes may depend on their cellular environment.
我们比较了大鼠肾α1A-和α1B样肾上腺素能受体与肌醇磷酸生成的偶联机制。实验在天然肾组织制剂以及用10μmol/L氯乙可乐定在37℃处理30分钟使α1B肾上腺素能受体失活的制剂中平行进行；大多数实验使用肾切片，但在某些情况下也使用分离的肾细胞。Ca2+螯合剂EGTA（5mmol/L）降低了天然肾组织中去甲肾上腺素刺激的肌醇磷酸生成，但增强了氯乙可乐定处理的肾切片中的生成。100nmol/L硝苯地平不能模拟EGTA的抑制作用。用500ng/ml百日咳毒素处理16 - 20小时使87%的细胞Gi失活，对分离肾细胞中去甲肾上腺素刺激的肌醇磷酸生成没有显著影响，但消除了氯乙可乐定的抑制作用。腺苷酸环化酶激活剂福斯可林（20μmol/L）抑制天然和氯乙可乐定处理切片中去甲肾上腺素刺激的肌醇磷酸生成，氯乙可乐定处理和福斯可林的抑制作用是相加的。我们得出结论，在大鼠肾脏中，通过α1B样肾上腺素能受体生成肌醇磷酸可能涉及细胞外Ca2+内流和百日咳毒素敏感的G蛋白，但对福斯可林的抑制不敏感。相比之下，α1A样肾上腺素能受体介导的肌醇磷酸生成不需要细胞外Ca2+或Gi的存在，且对福斯可林的抑制敏感。与其他模型系统已发表的数据相比，我们进一步得出结论，α1肾上腺素能受体亚型的信号传导机制可能取决于它们的细胞环境。
