GUANOSINE IS NEUROPROTECTIVE AGAINST OXYGEN/GLUCOSE DEPRIVATION SN HIPPOCAMPAL SLICES VIA LARGE CONDUCTANCE CA~(2+)-ACTIVATED K~+ CHANNELS, PHOSPHATIDILINOSITOL-3 KINASE/ PROTEIN KINASE B PATHWAY ACTIVATION AND GLUTAMATE UPTAKE

摘要

Guanine derivatives (GD) have been implicated in many relevant brain extracellular roles, such as modulation of giutamate transmission and neuronal protection against excitotoxic damage. GD are spontaneously released to the extracellular space from cultured astrocytes and during oxygen/glucose deprivation (OGD), The aim of this study has been to evaluate the potassium channels and phosphatidili-nositol-3 kinase (PI3K) pathway involvement in the mechanisms related to the neuroprotective role of guanosine in rat hippocampal slices subjected to OGD. The addition of guanosine (100 /M) to hippocampal slices subjected to 15 min of OGD and followed by 2 h of re-oxygenation is neuroprotective. The presence of K~+ channel blockers, glibencl-amide (20 (xM) or apamin (300 nM), revealed that neuroprotective effect of guanosine was not dependent on ATP-sen-sitive K~+ channels or small conductance Ca~(2+)-activated K~+ channels. The presence of charybdotoxin (100 nM), a large conductance Ca~(2+)-activated K~+ channel (BK) blocker, inhibited the neuroprotective effect of guanosine. Hippocampal slices subjected to OGD and re-oxygenation showed a significant reduction of giutamate uptake. Addition of guanosine in the re-oxygenation period has blocked the reduction of giutamate uptake. This guanosine effect was inhibited when hippocampal slices were pre-incubated with charybdotoxin or wortmanin (a PI3K inhibitor, 1 fiM) in the re-oxygenation period. Guanosine promoted an increase in Akt protein phos-phorylation. However, the presence of charybdotoxin blocked such effect. In conclusion, the neuroprotective effect of guanosine involves augmentation of giutamate uptake, which is modulated by BK channels and the activation of PI3K pathway. Moreover, neuroprotection caused by guanosine depends on the increased expression of phospho-Akt protein.