Release of secretory phospholipase A(2) from rat neuronal cells and its possible function in the regulation of catecholamine secretion

Here we show that secretory phospholipase A(2) (sPLA(2)) that is immunochemically indistinguishable from type II sPLA(2) is (i) stored in neuroendocrine cells, (ii) released in response to neurotransmitters or depolarization, and (iii) involved in the regulation of catecholamine secretion by these cells. Rat brain synaptic vesicle fractions contained PLA(2) activity, which was neutralized completely by an antibody raised against rat type II sPLA(2). sPLA(2) immunoreactive with anti-(type II sPLA(2)) antibody was released from synaptosomes in response to depolarization evoked by a high concentration of potassium in the presence of Ca2+. Rat pheochromocytoma PC12 cells, which differentiated into adherent cells similar to sympathetic neurons in response to nerve growth factor, were used for the detailed analysis of the dynamics and function of sPLA(2) in neuronal cells. Antibody against rat type II sPLA(2) precipitated similar to 80% of the PLA(2) activity in PC12 cell lysates. Transcript for type II sPLA(2) was detected in PC12 cells by reverse transcriptase-PCR. When neuronally differentiated PC12 cells were stimulated with carbamylcholine or potassium, sPLA(2) was released into the medium and reached a maximal similar to 40% release by 15 min. Inhibitors specific to type II sPLA(2) suppressed catecholamine secretion by PC12 cells which had been activated by carbamylcholine. Furthermore, treatment of PC12 cells with exogenous type II sPLA(2) alone elicited catecholamine secretion. These observations indicate that sPLA(2) released from neuronal cells may regulate the degranulation process leading to release of neurotransmitters and are compatible with our earlier finding that this enzyme is involved in the degranulation of rat mast cells.