Ajmat M T, Bonilla F, Hermosilla P C, Zelarayán L, Bühler M I
Instituto Superior de Investigaciones Biológicas (INSIBIO) Universidad Nacional de Tucumán Chacabuco 461 (4000) S.M. de Tucumán. Argentina.
Zygote. 2013 Aug;21(3):214-20. doi: 10.1017/S0967199411000645. Epub 2012 Feb 2.
Transient increases in the concentration of cytosolic Ca(2+) are essential for triggering egg activation events. Increased Ca(2+) results from its rapid release from intracellular stores, mainly mediated by one or both intracellular calcium channels: the inositol trisphosphate receptor (IP3R) and the ryanodine receptor (RyR). Several regulatory pathways that tailor the response of these channels to the specific cell type have been proposed. Among its many modulatory actions, calcium can serve as an activator of a cytosolic phospholipase A(2) (cPLA2), which releases arachidonic acid from phospholipids of the endoplasmic reticulum as well as from the nuclear envelope. Previous studies have suggested that arachidonic acid and/or its metabolites were able to modulate the activity of several ion channels. Based on these findings, we have studied the participation of the phospholipase A(2) (PLA(2)) pathway in the process of Bufo arenarum oocyte activation and the interrelation between any of its metabolites and the ion channels involved in the calcium release from the intracellular reservoirs at fertilization. We found that addition of both melittin, a potent PLA(2) activator, and arachidonic acid, the main PLA(2) reaction metabolite, was able to induce activation events in a bell-shaped manner. Differential regulation of IP3Rs and RyRs by arachidonic acid and its products could explain melittin and arachidonic acid behaviour in Bufo arenarum egg activation. The concerted action of arachidonic acid and/or its metabolites could provide controlled mobilization of calcium from intracellular reservoirs and useful tools for understanding calcium homeostasis in eggs that express both types of receptors.
胞质Ca(2+)浓度的短暂升高对于触发卵子激活事件至关重要。Ca(2+)浓度升高是由于其从细胞内储存库快速释放，主要由一种或两种细胞内钙通道介导：肌醇三磷酸受体（IP3R）和兰尼碱受体（RyR）。已经提出了几种调节这些通道对特定细胞类型反应的调节途径。在其众多调节作用中，钙可作为胞质磷脂酶A(2)（cPLA2）的激活剂，该酶从内质网以及核膜的磷脂中释放花生四烯酸。先前的研究表明，花生四烯酸和/或其代谢产物能够调节几种离子通道的活性。基于这些发现，我们研究了磷脂酶A(2)（PLA(2)）途径在中华大蟾蜍卵母细胞激活过程中的参与情况，以及其任何代谢产物与受精时参与细胞内储存库钙释放的离子通道之间的相互关系。我们发现，添加蜂毒肽（一种有效的PLA(2)激活剂）和花生四烯酸（主要的PLA(2)反应代谢产物）都能够以钟形方式诱导激活事件。花生四烯酸及其产物对IP3Rs和RyRs的差异调节可以解释蜂毒肽和花生四烯酸在中华大蟾蜍卵子激活中的行为。花生四烯酸和/或其代谢产物的协同作用可以提供从细胞内储存库中可控的钙动员，并为理解表达两种受体类型的卵子中的钙稳态提供有用的工具。
