Lysophosphatidylcholine induces arachidonic acid release and calcium overload in cardiac myoblastic H9c2 cells

Lysophosphatidylcholine (lyso-PC) and arachidonate are products of phosphatidylcholine hydrolysis by phospholipase A₂. In this study, the modulation of arachidonate release by exogenous lyso-PC in rat heart myoblastic H9c2 cells was examined. Incubation of H9c2 cells with lyso-PC resulted in an enhanced release of arachidonate in both a time- and dose- dependent fashion. Lyso-PC species containing palmitoyl (C(16:0)) or stearoyl (C(18:0)) groups evoked the highest amount of arachidonate release, while other lysophospholipid species were relatively ineffective. Cells treated with phospholipase A₂ inhibitors resulted in the attenuation of the enhanced arachidonate release in the presence of lyso-PC. Lyso-PC caused the translocation of phospholipase A₂ from the cytosol to the membrane fraction and induced an increase in Ca²⁺ flux from the medium into the cells. Nimodipine, a specific Ca²⁺-channel blocker, partially attenuated the lyso- PC-induced rise in intracellular Ca²⁺. Concurrent with Ca²⁺ influx, lyso- PC caused an enhancement of protein kinase C activity. The lyso-PC-induced arachidonate release was attenuated when cells were preincubated with specific protein kinase C and mitogen activated protein kinase kinase inhibitors. Taken together, these results strongly indicate that the lyso-PC- induced increases in levels of intracellular calcium and stimulation of protein kinase C lead to the activation of cytosolic phospholipase A₂ which results in the enhancement of arachidonate release in H9c2 cells.