Swelling-Induced Arachidonic Acid Release via the 85-kDa cPLA2in Human Neuroblastoma Cells

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Abstract
Basavappa, Srisaila, Stine F. Pedersen, Nanna K. Jørgensen, J. Clive Ellory, and Else K. Hoffmann. Swelling-induced arachidonic acid release via the 85-kDa cPLA2in human neuroblastoma cells. J. Neurophysiol. 79: 1441–1449, 1998. Arachidonic acid or its metabolites have been implicated in the regulatory volume decrease (RVD) response after hypotonic cell swelling in some mammalian cells. The present study investigated the role of arachidonic acid (AA) during RVD in the human neuroblastoma cell line CHP-100. During the first nine minutes of hypo-osmotic exposure the rate of3H-arachidonic acid (3H-AA) release increased to 250 ± 19% (mean ± SE, n = 22) as compared with cells under iso-osmotic conditions. This release was significantly inhibited after preincubation with AACOCF3, an inhibitor of the 85-kDa cytosolic phospholipase A2(cPLA2). This indicates that a PLA2, most likely the 85-kDa cPLA2is activated during cell swelling. In contrast, preincubation with U73122, an inhibitor of phospholipase C, did not affect the swelling-induced release of3H-AA. Swelling-activated efflux of36Cl and3H-taurine were inhibited after preincubation with AACOCF3. Thus the swelling-induced activation of cPLA2may be essential for stimulation of both36Cl and3H-taurine efflux during RVD. As the above observation could result from a direct effect of AA or its metabolite leukotriene D4(LTD4), the effects of these agents were investigated on swelling-induced36Cl and3H-taurine effluxes. In the presence of high concentrations of extracellular AA, the swelling-induced efflux of36Cl and3H-taurine were inhibited significantly. In contrast, addition of exogenous LTD4had no significant effect on the swelling-activated36Cl efflux. Furthermore, exogenous AA increased cytosolic calcium levels as measured in single cells loaded with the calcium sensitive dye Fura-2. On the basis of these results we propose that cell swelling activates phospholipase A2and that this activation via an increased production of AA or some AA metabolite(s) other than LTD4is essential for RVD.