Swelling-induced arachidonic acid release via the 85-kDa cPLA2 in human neuroblastoma cells

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 of H-3-arachidonic acid (H-3-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 AACOCF(3), an inhibitor of the 85-kDa cytosolic phospholipase A(2) (cPLA(2)). This indicates that a PLA(2), most likely the 85-kDa cPLA(2) is activated during cell swelling. In contrast, preincubation with U73122, an inhibitor of phospholipase C, did not affect the swelling-induced release of H-3-AA. Swelling-activated efflux of 36Cl and H-3-taurine were inhibited after preincubation with AACOCF(3). Thus the swelling-induced activation of cPLA(2) may be essential for stimulation of both 36Cl and H-3-taurine efflux during RVD. As the above observation could result from a direct effect of AA or its metabolite leukotriene D-4 (LTD4), the effects of these agents were investigated on swelling-induced Cl-36 and H-3-taurine effluxes. In the presence of high concentrations of extracellular AA, the swelling-induced efflux of Cl-36 and H-3-taurine were inhibited significantly. In contrast, addition of exogenous LTD4 had no significant effect on the swelling-activated Cl-36 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 A(2) and that this activation via an increased production of AA or some AA metabolite(s) other than LTD4 is essential for RVD.