Apamin,a selective blocker of SKCa channels,inhibits posthypoxic hyperexcitability but does not affect rapid hypoxic preconditioning in hippocampal CA1 pyramidal neurons in vitro

The aim of this study was to investigate the effects of apamin, a selective blocker of SK_Ca channels, on the repeated brief hypoxia-induced posthypoxic hyperexcitability and rapid hypoxic preconditioning in hippocampal CA1 pyramidal neurons in vitro. The method of field potentials measurement in CA1 region of the rat hippocampal slices was used. Application of apamin (50 nM) to the hippocampal slices during hypoxic episodes significantly abolished posthypoxic hyperexcitability induced by brief hypoxic episodes. However, in contrast to our previous results with iberiotoxin, a selective blocker of BK_Ca channels, apamin significantly enhanced the depressive effect of brief hypoxia on the PS amplitude during hypoxic episode and did not abolish the rapid hypoxic preconditioning in CA1 pyramidal neurons. Present results indicate that SK_Ca channels, along with previously implicated BK_Ca channels, play an important role in the development of posthypoxic hyperexcitability induced by brief hypoxic episodes in CA1 pyramidal neurons. However, SK_Ca channels, in contrast to the BK_Ca channels, are not involved in the rapid hypoxic preconditioning in CA1 hippocampal region in vitro.