Pharmacological blockade of Cl- pumps or Cl- channels reduces the adenosine-mediated depression of stimulus train-evoked Ca2+ fluxes in rat hippocampal slices.

Stimulus train-evoked decreases of the extracellular Ca2+ concentration (delta Ca) were measured with ion-sensitive electrodes in the CA1 area of rat hippocampal slices. The adenosine receptor antagonist, theophylline, led to a marked increase of delta Ca in the synaptic and in the soma layer reflecting an increased activation and enhanced frequency potentiation of pyramidal neurons in the absence of endogenous adenosine action. The theophylline effect was significantly reduced in the presence of the C1 channel blocker, 4,4'-diisothiocyano-2,2'-stilbenedisulfonate (DIDS) or of the Cl- pump blocker, furosemide. The data indicate that the adenosine-mediated modulation of the repetitive input strength is related to the function of Cl- ions.