Contribution of GABA(A)-mediated conductances to anoxia-induced depolarization

CA1 pyramids were studied intracellularly in rat hippocampal slices to establish the contribution of excitatory amino acid (EAA) and GABA(A) receptors to the depolarizations induced by brief (< 10 min) anoxic episodes. An increase of the amplitude of the depolarizations evoked by successive anoxic episodes occurred with KCl (n=4 cells), not with K-acetate-filled (n=3) recording electrodes. Moreover, with K-acetate-filled electrodes the anoxic depolarization amplitude was reduced, but not abolished by EAA receptor antagonists (n=14). The residual anoxic depolarizations were blocked by a GABA(A) receptor antagonist (n=5) and decreased by the carbonic anhydrase inhibitor acetazolamide (n=4). We conclude that the anoxic depolarizations generated by CA1 pyramids are caused by the activation of EAA along with GABA(A) receptors leading to an increased membrane conductance to both Cl- and HCO3-.