Secreted phospholipase A2 potentiates glutamate-induced calcium increase and cell death in primary neuronal cultures

Secreted phospholipases A(2) (sPLA(2)s) modulate neuronal survival and neurotransmitter release. Here we show that sPLA(2) (group III) synergistically increases glutamate-induced cell death and intracellular calcium ([Ca2+](i)) in cultured primary cortical and hippocampal neurons. Whereas 1 muM glutamate elicited transient [Ca2+](i) increases in all neurons that recovered 66% to baseline, 25 ng/ml sPLA(2) pretreatment resulted in sustained [Ca2+]i increases, with only 5% recovery. At 250 nM glutamate, 25% of neurons failed to respond, and the average recovery time was 101 +/- 12 sec; sPLA(2) increased recovery time to 158 +/- 6 sec, and only 2% of cells failed to respond. Both the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 and the calcium-channel blocker cobalt inhibited this effect. Experiments with the glutamate uptake inhibitor L-trans-pyrollidine-2,4-dicarboxylic acid (2.5 muM) indicated that glutamate uptake sites are not a likely modulation point by sPLA(2), whereas arachidonic acid (AA) potentiated calcium responses to glutamate. Thus the enhancement of glutamate-induced [Ca2+]i increases by sPLA(2) may be due to modulation at NMDA receptors and/or calcium channels by AA. These results indicate that sPLA(2) affects neuronal responses to both nontoxic (0.1-10 muM) and toxic (=25 muM) concentrations of glutamate, implicating this enzyme in neuronal functions in pathology. (C) 2002 Wiley-Liss, Inc.