Yang M, Büscher R, Taguchi K, Grübbel B, Insel P A, Michel M C
Department of Medicine, University of Essen, Germany.
J Pharmacol Exp Ther. 1998 Jul;286(1):36-43.
We examined the down-regulation of alpha-1B adrenoceptors in Madin-Darby canine kidney D1 (MDCK) cells with an emphasis on a possible role of protein kinase C. The alpha-1 adrenoceptor agonist phenylephrine (1-100 microM) concentration-dependently down-regulated alpha-1B adrenoceptors in MDCK cells. Down-regulation by 100 microM phenylephrine was detectable after 2 hr and maximal after 8 to 24 hr. The receptor down-regulation was accompanied by a decrease in phenylephrine-stimulated inositol phosphate formation but not by an altered expression of immunodetectable Gq/11 alpha subunits. Even though alpha-1B adrenoceptor and P2 purinergic receptor stimulation promote prostaglandin E2 formation, receptor down-regulation was not prevented by indomethacin (10 microM) treatment but was partly mimicked by treatment with the purinergic receptor agonists adenosine-5'-O-(3-thio)triphosphate and 2-methylthio-ATP (300 microM each). Phorbol-12-myristate-13-acetate (1-100 nM) concentration-dependently down-regulated MDCK alpha-1B adrenoceptors to a greater extent than did phenylephrine. Three protein kinase C inhibitors, H7 (100 microM), staurosporine (100 nM) and KT5926 (1 microM), markedly attenuated receptor down-regulation promoted by phorbol ester but did not affect that by phenylephrine. Two inhibitors of Ca++/calmodulin protein kinase pathways, KT5926 (1 microM) and W-7 (30 microM), also failed to prevent phenylephrine-induced down-regulation of alpha-1B adrenoceptors. We conclude that agonist-induced down-regulation of MDCK cell alpha-1B adrenoceptors is mimicked by a protein kinase C-activating phorbol ester but that the second messenger kinases protein kinase C and Ca++/calmodulin protein kinase do not mediate agonist-induced down-regulation of the alpha-1B adrenoceptor.
我们研究了马-达二氏犬肾D1（MDCK）细胞中α-1B肾上腺素能受体的下调情况，重点关注蛋白激酶C的可能作用。α-1肾上腺素能受体激动剂去氧肾上腺素（1 - 100微摩尔）在MDCK细胞中浓度依赖性地下调α-1B肾上腺素能受体。100微摩尔去氧肾上腺素引起的下调在2小时后可检测到，8至24小时后达到最大程度。受体下调伴随着去氧肾上腺素刺激的肌醇磷酸生成减少，但免疫可检测的Gq/11α亚基的表达没有改变。尽管α-1B肾上腺素能受体和P2嘌呤能受体刺激可促进前列腺素E2的生成，但吲哚美辛（10微摩尔）处理并不能阻止受体下调，而嘌呤能受体激动剂5'-O-(3-硫代)三磷酸腺苷和2-甲硫基-ATP（各300微摩尔）处理则部分模拟了这种下调。佛波醇-12-肉豆蔻酸酯-13-乙酸酯（1 - 100纳摩尔）比去氧肾上腺素在更大程度上浓度依赖性地下调MDCKα-1B肾上腺素能受体。三种蛋白激酶C抑制剂，H7（100微摩尔）、星形孢菌素（100纳摩尔）和KT5926（1微摩尔），显著减弱了佛波酯促进的受体下调，但不影响去氧肾上腺素引起的下调。两种Ca++/钙调蛋白蛋白激酶途径抑制剂，KT5926（1微摩尔）和W-7（30微摩尔），也未能阻止去氧肾上腺素诱导的α-1B肾上腺素能受体下调。我们得出结论，激动剂诱导的MDCK细胞α-1B肾上腺素能受体下调可被激活蛋白激酶C的佛波酯模拟，但第二信使激酶蛋白激酶C和Ca++/钙调蛋白蛋白激酶并不介导激动剂诱导的α-1B肾上腺素能受体下调。
