Rapid preconditioning neuroprotection following anoxia in hippocampal slices: role of the K+ ATP channel and protein kinase C.

Sublethal cerebral anoxic/ischemic insults may "precondition" and thereby protect brain from subsequent anoxic/ischemic insults. We tested two hypotheses in hippocampal slices: (i) that short periods of anoxia, each followed by reoxygenation, precondition and thereby improve recovery of synaptic activity following "lethal" anoxic insults; and (ii) that the ATP-sensitive potassium channel [K+ ATP] or protein kinase C mediates anoxic preconditioning neuroprotection in hippocampal slices. Hippocampal slices were subjected to three short periods of anoxia, each separated by 10 min of reoxygenation. These anoxic insults were prolonged only until the onset of anoxic depolarization. Thirty minutes following these insults, slices underwent a "test" anoxic insult, which was characterized by an anoxic insult that lasted 1 min of anoxic depolarization. Recovery of evoked potential amplitudes was followed for 30 min of reoxygenation. The beneficial effects of preconditioning was shown by the significant recovery of evoked potentials after "test" anoxic insults in preconditioned slices, when compared to controls that only underwent a "test" anoxic insult. In control slices, transient superfusion with an ATP-sensitive potassium channel agonist (10 microM pinacidil) 30 min prior to "test" anoxia markedly improved evoked potential recovery. Administration of 5 microM of the sulfonylurea tolbutamide, an ATP-sensitive potassium channel antagonist during preconditioning insults, blocked the protection afforded by preconditioning. Transient superfusion of a protein kinase C activator (500 nM phorbol 12-myristate 13-acetate) did not improve evoked potential recovery. Administration of 50 nM chelerythrine, a protein kinase C inhibitor during preconditioning insults did not block the protection afforded by preconditioning. These data support the hypothesis that the ATP-sensitive potassium channel is involved in the neuroprotection afforded by anoxic preconditioning in hippocampal slices. However, protein kinase C activation does not appear to play a role in this neuroprotection.