O-2 deprivation inhibits Ca2+-activated K+ channels cytosolic factors in mice neocortical neurons

O-2 deprivation induces membrane depolarization in mammalian central neuron s. It is possible that this anoxia-induced depolarization is partly mediate d 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 con figurations, but only one of them was sensitive to lack of O-2. This O-2-se nsitive K+ channel was identified as a large-conductance Ca2+-activated Kchannel (BKCa) as it exhibited a large conductance of 210 pS under symmetri cal 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 th e effect of O-2 deprivation on BKCa channels of mice neocortical neurons wa s mediated via cytosol-dependent processes. Lowering intracellular pH (pH(i )) or cytosolic addition of the catalytic subunit of a cAMP-dependent prote in kinase A in the presence of Mg-ATP, caused a decrease in BKCa, channel a ctivity by reducing the sensitivity of this channel to Ca2+. In contrast, t he reducing agents glutathione and DTT increased single BKCa channel open p robability without affecting unitary conductance. We suggest that in neocor tical neurons, (a) BKCa is modulated by O-2 deprivation via cytosolic facto rs and cytosol-dependent processes, and (b) the reduction in channel activi ty during hypoxia is likely due to reduced Ca2+ sensitivity resulting from cytosolic alternations such as in pH(i) and phosphorylation. Because of the ir large conductance and prevalence in the neocortex, BKCa channels may be considered as a target for pharmacological intervention in conditions of ac ute anoxia or ischemia.