cPLA2alpha-evoked formation of arachidonic acid and lysophospholipids is required for exocytosis in mouse pancreatic beta-cells

• Published in: American journal of physiology: endocrinology and metabolism Vol. 48; no. 1; p. E73
• Main Authors: Juhl, Kirstine, Hoy, Marianne, Olsen, Hervor L, Bokvist, Krister
• Format: Journal Article
• Language: English
• Published: Bethesda American Physiological Society 01.07.2003
• Subjects: Acids; Arachnids; Cells; Pancreas; Phosphorus; Rodents
• ISSN: 0193-1849; 1522-1555

Using capacitance measurements, we investigated the effects of intracellularly applied recombinant human cytosolic phospholipase A2 (cPLA2) and its lipolytic products arachidonic acid and lysophosphatidylcholine on Ca2+-dependent exocytosis in single mouse pancreatic -cells. cPLA2 dose dependently (EC50 = 86 nM) stimulated depolarization-evoked exocytosis by 450% without affecting the whole cell Ca2+ current or cytoplasmic Ca2+ levels. The stimulatory effect involved priming of secretory granules as reflected by an increase in the size of the readily releasable pool of granules from 70-80 to 280-300. cPLA2-stimulated exocytosis was antagonized by the specific cPLA2 inhibitor AACOCF3. Ca2+-evoked exocytosis was reduced by 40% in cells treated with AACOCF3 or an antisense oligonucleotide against cPLA2. The action of cPLA2 was mimicked by a combination of arachidonic acid and lysophosphatidylcholine (470% stimulation) in which each compound alone doubled the exocytotic response. Priming of insulin-containing secretory granules has been reported to involve Cl- uptake through ClC-3 Cl- channels. Accordingly, the stimulatory action of cPLA2 was inhibited by the Cl- channel inhibitor DIDS and in cells pretreated with ClC-3 Cl- channel antisense oligonucleotides. We propose that cPLA2 has an important role in controlling the rate of exocytosis in -cells. This effect of cPLA2 reflects an enhanced transgranular Cl- flux, leading to an increase in the number of granules available for release, and requires the combined actions of arachidonic acid and lysophosphatidylcholine. [PERIODICAL ABSTRACT]