O2 deprivation inhibits Ca2+-activated K+ channels cytosolic factors in mice neocortical neurons

O-2 deprivation induces membrane depolarization in mammalian central neurons. It is possible that this anoxia-induced depolarization is partly mediated by an inhibition of K+ channels. We therefore performed experiments using patch-clamp techniques and dissociated neurons from mice neocortex. Three types of K+ channels were observed in both cell-attached and inside-out configurations, but only one of them was sensitive to lack of O-2. This O-2-sensitive K+ channel was identified as a large-conductance Ca2+-activated K+ channel (BKCa) as it exhibited a large conductance of 210 pS under symmetrical K+ (140 mM) conditions, a strong voltage-dependence of activation, and a marked sensitivity to Ca2+. A low-O-2 medium (PO2 = 10-20 mmHg) markedly inhibited this BKCa channel open probability in a voltage-dependent manner in cell-attached patches, but not in inside-out patches, indicating that the effect of O-2 deprivation on BKCa channels of mice neocortical neurons was mediated via cytosol-dependent processes. Lowering intracellular pH (pH(i)) or cytosolic addition of the catalytic subunit of a cAMP-dependent protein kinase A in the presence of Mg-ATP, caused a decrease in BKCa, channel activity by reducing the sensitivity of this channel to Ca2+. In contrast, the reducing agents glutathione and DTT increased single BKCa channel open probability without affecting unitary conductance. We suggest that in neocortical neurons, (a) BKCa is modulated by O-2 deprivation via cytosolic factors and cytosol-dependent processes, and (b) the reduction in channel activity during hypoxia is likely due to reduced Ca2+ sensitivity resulting from cytosolic alternations such as in pH(i) and phosphorylation. Because of their large conductance and prevalence in the neocortex, BKCa channels may be considered as a target for pharmacological intervention in conditions of acute anoxia or ischemia.