Ion Channel Involvement in Anoxic Depolarization Induced by Cardiac Arrest in Rat Brain

Abstract

Anoxic depolarization (AD) and failure of ion homeostasis play an important role in ischemia-induced neuronal injury. In the present study, different drugs with known ion-channel-modulating properties were examined for their ability to interfere with cardiac-arrest-elicited AD and with the changes in the extracellular ion activity in rat brain. Our results indicate that only drugs primarily blocking membrane Na⁺ permeability (NBQX, R56865, and flunarizine) delayed the occurrence of AD, while compounds affecting cellular Ca²⁺ load (MK-801 and nimodipine) did not influence the latency time. The ischemia-induced [Na⁺]_e reduction was attenuated by R56865. Blockade of the ATP-sensitive K⁺ channels with glibenclamide reduced the [K⁺]_e increase upon ischemia, indicating an involvement of the K_ATP channels in ischemia-induced K⁺ efflux. The K_ATP channel opener cromakalim did not affect the AD or the [K⁺]_e concentration. The ischemia-induced rapid decline of extracellular calcium was attenuated by receptor-operated Ca²⁺ channel blockers MK-801 and NBQX, but not by the voltage-operated Ca²⁺ channel blocker nimodipine, R56865, and flunarizine.