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 immun ochemically indistinguishable from type II sPLA(2) is (i) stored in ne uroendocrine 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 contain ed PLA(2) activity, which was neutralized completely by an antibody ra ised against rat type II sPLA(2). sPLA(2) immunoreactive with anti-(ty pe II sPLA(2)) antibody was released from synaptosomes in response to depolarization evoked by a high concentration of potassium in the pres ence of Ca2+. Rat pheochromocytoma PC12 cells, which differentiated in to 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 s PLA(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 release d into the medium and reached a maximal similar to 40% release by 15 m in. Inhibitors specific to type II sPLA(2) suppressed catecholamine se cretion by PC12 cells which had been activated by carbamylcholine. Fur thermore, treatment of PC12 cells with exogenous type II sPLA(2) alone elicited catecholamine secretion. These observations indicate that sP LA(2) released from neuronal cells may regulate the degranulation proc ess leading to release of neurotransmitters and are compatible with ou r earlier finding that this enzyme is involved in the degranulation of rat mast cells.