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

本文研究了肾上腺嗜铬细胞原代培养过程中胆碱能受体功能由毒蕈碱型向烟碱型转变的机制，这种转变涉及胞浆Ca^++动员和三磷酸肌醇（IP_3）。在培养0.5天时，毒蕈碱（M受体的特异性激动剂）对细胞内Ca^2+动员和Ins（1，3，4）P_3积累的影响大于烟碱特异性激动剂尼古丁。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。在0.5d时，M受体拮抗剂阿托品可明显抑制非特异性激动剂卡巴胆碱诱导的InsP_3积累，而在5d时，阿托品的抑制作用明显减弱。另一方面，烟碱受体拮抗剂六甲双铵和筒箭毒碱显示出更高的抑制效力，在5天相比，0.5天的文化。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+动员作用的减弱是由于毒蕈碱受体本身消失的可能性。这些结果表明，在原代培养的肾上腺嗜铬细胞中，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型转变为烟碱型。

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.