Menbrane phospholipase c activation and signal transduction in relation to change of receptor-linkage mechanism

研究了肾上腺染色质细胞原代培养过程中细胞内Ca^<++>动员和肌醇三磷酸（IP_3）的功能由毒碱受体向烟碱能受体转变的机制。在培养0.5 d时，毒蕈碱（一种毒蕈碱受体的特异性激动剂）对细胞内Ca^<2+>的动员和Ins(1,3,4)P_3的积累的影响比尼古丁特异性激动剂更大。相反，在第5天，尼古丁对Ins(1,3,4)P_3的积累和细胞内钙动员的影响大于毒蕈碱。此外，在0.5 d时，毒蕈碱拮抗剂阿托品强烈抑制非特异性激动剂卡巴醇诱导的InsP_3积累的增加，而在5 d时，阿托品的抑制作用大大降低。另一方面，烟碱受体拮抗剂六甲溴铵和-管库碱在培养5天时的抑制作用明显高于0.5天。与毒蕈碱配体的结合实验排除了毒蕈碱对InsP_3和细胞内Ca^<2+>动员的作用减弱是由于毒蕈碱受体本身消失的可能性。这些数据表明，在肾上腺染色质细胞原代培养过程中，与InsP_3积累和Ca^<2+>动员相关的胆碱能受体在功能上从毒蕈碱向烟碱转变。

The mechanism of functional shift from muscarinic to nicotinic cholinergic receptors involved in cytosolic Ca^<++> mobilization and inositol triphosphate (IP_3) during the primary culture of adrenal chromaffin cells was studied. At 0.5 day in culture, muscarine, a specific agonist for muscarinic receptors, caused a greater effect on intracellular Ca^<2+> mobilization and the accumulation of Ins(1,3,4)P_3 than did the nicotinic-specific agonist nicotine. On the contrary, at 5 days, nicotine produced a greater effect on the accumulation of Ins(1,3,4)P_3 and intracellular calcium mobilization than did muscarine. Furthermore, at 0.5 day, the muscarinic antagonist atropine strongly inhibited the increase in InsP_3 accumulation that was induced by the nonspecific agonist carbachol, whereas at 5 days the inhibitory effect of atropine was greatly lowered. On the other hand, the nicotinic receptor antagonists hexamethonium and - tubocurarine showed a much higher inhibitory potency at 5 days compared with 0.5 day in culture. Binding experiments with a muscarinic ligand excluded the possibility that the reduction in muscarinic effects on InsP_3 and intracellular Ca^<2+> mobilization were due to disappearance of the muscarinic receptor itself. These data show that cholinergic receptors linked to the accumulation of InsP_3 and Ca^<2+> mobilization functionally shift from muscarinic to nicotinic during primary culture of adrenal chromaffin cells.