Research Article

Role of phospholipase A₂ pathway in regulating activation of Bufo arenarum oocytes

M.T. Ajmat^a2, F. Bonilla^a2, P.C. Hermosilla^a3, L. Zelarayán^a2 and M.I. Bühler^a1 c1

^a1 Departamento de Biología del Desarrollo (INSIBIO), Chacabuco 461, 4000- San Miguel de Tucumán, Argentina.

^a2 Instituto Superior de Investigaciones Biológicas (INSIBIO) Universidad Nacional de Tucumán Chacabuco 461 (4000) S.M. de Tucumán. Argentina.

^a3 Instituto de Biología Facultad de Bioquímica, Química y Farmacia Universidad Nacional de Tucumán, Argentina.

Summary

Transient increases in the concentration of cytosolic Ca²⁺ are essential for triggering egg activation events. Increased Ca²⁺ 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 A₂ (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 A₂ (PLA₂) 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 PLA₂ activator, and arachidonic acid, the main PLA₂ 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.

(Received January 10 2011)

(Accepted May 28 2011)

Keywords:

• Bufo arenarum;
• Oocytes activation;
• Phospholipase A₂

Correspondence:

^c1 All correspondence to: Marta Bühler. Departamento de Biología del Desarrollo (INSIBIO), Chacabuco 461, 4000- San Miguel de Tucumán, Argentina. Fax: +54 381 4247752 (ext. 7004). e-mail: mbuhler@fbqf.unt.edu.ar