SELECTIVE NEUROTOXICITY INDUCED BY THE IONOPHORE LASALOCID IN RAT DISSOCIATED CEREBRAL CULTURES, INVOLVEMENT OF THE NMDA RECEPTOR CHANNEL/

An in vitro model of dissociated cerebral cultures, prepared from pren atal 15-16-days rat fetuses, was used to further characterize the neur otoxic effects caused by the antibiotic ionophore lasalocid - X-537A. The damage caused by lasalocid (1-2 mu M, 2-4 hr) included swelling of perikarya, followed by cytolysis of most neurons present in the cultu res. The neuronal damage was dose-dependent, noticeable at concentrati ons above 0.5 mu M, and was more pronounced in established cultures (1 4 days in vitro - DIV) than in younger ones (7 DIV). Unlike neurons, n o damage was observed in glia and other non-neuronal cells present in the cultures by exposure to 2 mu M lasalocid. Moreover, the drug was n ot toxic for cultures of rat astrocytes and C6 glioma cells. Another c alcium ionophore A-23187 (calcimycin, 1 mu M) destroyed both neuronal and non-neuronal cells within 1 hr. Ca2+ influx was increased by 140% in cultures exposed to lasalocid (1.5 mu M). The lasalocid neurotoxic effects were neither inhibited by 10 mu M nimodipine (a calcium channe l antagonist) nor by 10 mu M 6-Cyano-7-nitroquinoxaline-2,3-dione (CNQ X)(a non-N-methyl-D-aspartic acid (NMDA) receptor antagonist), but wer e exclusively blocked by 10 mu M MK-801 (a non-competitive NMDA recept or/channel antagonist). The neurotoxicity induced by lasalocid was fur ther confirmed by measurements of lactate dehydrogenase (LDH) released into the media. Lasalocid (1.5 mu M) induced the release of both LDH and arachidonic acid (AA) (by 8 and 4 fold of control values, respecti vely), and this was blocked by MK-801 but not by CNQX. These results a re in according with the observations that activation of calcium influ x through the NMDA receptor leads to activation of phospholipase A(2) (PLA(2)) and release of AA. In contrast, MK-801 did not block the rele ase of either LDH or AA mediated by the calcium ionophore A-23187 (1 m u M) in these cultures. [H-3]-MK-801 binding to washed rat cortical me mbranes, a measure of direct interaction with the NMDA receptor/channe l complex, was nor affected by lasalocid either alone or in the presen ce of glutamate and glycine. [H-3]-D-aspartate release, a measure of e xcitatory amino acid (EAA) secretion media ted by NMDA receptor activa tion, was increased by lasalocid and could be blocked by MK-801. These observations suggest that lasalocid induces selective neurotoxicity, which involves the NMDA receptor/channel complex, possibly indirectly, resulted in elevated intracellular Ca2+ levels and the subsequent glu tamate or aspartate release. (C) 1996 Intox Press, Inc.