Cl- transporter block enhances GABAergic spontaneous activity in rat hippocampal CA3 cells

Chloride-cation Transporter Blockers (CTBs) furosemide and ammonium were used to test the effects of changes in the internal [Cl-] on the spontaneous and miniature GABAergic post-synaptic currents (PSCs) of CA3 pyramidal cells of rat hippocampal slices with the whole-cell patch technique. Application of CTBs in the presence of kynurenic acid raised (65 +/- 21%) the frequency of GABAergic spontaneous PSCs leaving unchanged the miniature frequency, indicating that the increase in synaptic activity was caused by interneurone firing. Partial removal of external chloride yielded the same effect, suggesting that ECl contributes to the resting potential of interneurones. PSC rise times were prolonged and their mean amplitude was lowered by furosemide as well as the response to exogenous muscimol, confirming that furosemide exerts some GABAA receptor antagonism.