Calcium mobilization by muscarinic receptors and ATP receptors during retinogenesis

乙酰胆碱和三磷酸腺苷（ATP）可通过M受体和P_嘌呤受体<2U>释放早期鸡胚视网膜细胞内钙库中的Ca ^2+，从而增加细胞内Ca ^2+浓度。我们用Fura-2荧光技术研究了毒蕈碱和嘌呤能Ca ^2+反应的信号转导机制以及嘌呤能Ca^2+反应的发育变化，结果表明，百日咳毒素抑制ATP诱导的Ca^2+升高，而对毒蕈碱型Ca^2+升高无抑制作用。磷脂酶C抑制剂U-73122可抑制ATP引起的Ca^2+升高，但其类似物U-73343不能抑制ATP引起的Ca^2+升高，相反，U-73122和U-73343均抑制毒蕈碱引起的Ca^2+升高。抑制磷脂酰肌醇代谢的Li^+可增强毒蕈碱能和嘌呤能Ca^2+的升高。Thapsigargin是三磷酸肌醇（IP_3）敏感性Ca ^2+商店的Ca^2+-ATP酶抑制剂，它能消除毒蕈碱和嘌呤能Ca^2+升高。毒蕈碱能和嘌呤能Ca^2+动员之间发生了相互作用，但它们并不闭塞。我们的研究结果表明，毒蕈碱能和嘌呤能的Ca^&lt;2+&gt;动员都是利用IP_3敏感的Ca^&lt;2+&gt;库，但两者之间的信号转导途径不同，ATP诱导的Ca^&lt;2+升高在E3时最显著，到E8时急剧下降，并进一步下降，直到突触形成前的E11-13。ATP可能在鸡视网膜神经发生的早期起细胞间信使的作用。

Acetylcholine and adenosine triphosphate (ATP) raise intracellular Ca^<2+> concentration via muscarinic receptors and P_<2U> purinoceptors by releasing Ca^<2+> from intracellular Ca^<2+> stores in the neural retina of early embryonic chick. We studied the signal transduction mechanisms for the muscarinic and purinergic Ca^<2+> responses and developmental changes in the purinergic Ca^<2+> responses with fura-2 fluorescence measurements.Pertussis toxin suppressed the ATP-induced Ca^<2+> rise, whereas no inhibition was observed on the muscarinic Ca^<2+> rise. U-73122, an inhibitor of phospholipase C,suppressed the Ca^<2+> rise to ATP,but its analog U-73343 did not suppress it. In contrast, both U-73122 and U-73343 suppressed the muscarinic Ca^<2+> rise. Li^+, which inhibits phosphatidylinositol metabolism, enhanced both the muscarinic and purinergic Ca^<2+> rises. Thapsigargin, an inhibitor of Ca^<2+>-ATPase of inositol trisphosphate (IP_3) -sensitive Ca^<2+> stores, abolished both the muscarinic and purinergic Ca^<2+> rises. Cross-talk occurred between the muscarinic and purinergic Ca^<2+> mobilizations but they were not occlusive. Our study suggests that both the muscarinic and purinergic Ca^<2+> mobilizations utilize IP_3-sensitive Ca^<2+> stores, but different signal transduction pathways are involved in between the muscarinic and purinergic Ca^<2+> responses.The ATP-induced Ca^<2+> rise was the most prominent at E3, drastically declined towards E8 and further decreased until E11-13 before synapse formation. ATP might act as an intercellular messenger during the early period of neurogenesis in the chick retina.