Evidence from cultured rat cortical neurons of differences in the mechanism of ischemic preconditioning of brain and heart

Ca2+ influx and activation of protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) during nonlethal ischemic preconditioning have been i mplicated in the protection of the heart against subsequent lethal ischemic injury. Thus, we determined if Ca2+ influx, PKC and MAPK also mediate isch emic preconditioning-induced protection in neurons. Preconditioning by expo sure of E18 rat cortical cultures to 90 min of nonlethal oxygen-glucose dep rivation (OGD) 24 h prior to 180-240 min of lethal OGD was neuroprotective. Exposure to nominally free Ca2+, or blockade of the alpha-amino-hydroxy-5- methyl-isoxazolepropionate (AMPA) receptor with CNQX did not eliminate prot ection. MAPK activity did not change and PKC activity decreased by 50% rela tive to normal baseline levels at 0 and 24 h following preconditioning. The sustained decrease in PKC activity was not due to a loss of enzyme as dete rmined from immunoblots using pan and epsilon-, beta- and zeta-specific PKC antibodies. Neuroprotection was maintained with pharmacological inhibition of PKC activity by staurosporine, chelerythrine and calphostin C and MAPK activity by PD 98059 during preconditioning, indicating that activation of these enzymes during preconditioning was not necessary for protection. Ther efore, in contrast to cardiac tissue, ischemic preconditioning of neurons d oes not require activation of PKC and MAP kinase, and protection is maintai ned with substantial removal of extracellular Ca2+ or blockade of the AMPA receptor. (C) 1999 Published by Elsevier Science B.V. All rights reserved.