Mechanism of excitatory amino acid-induced accumulation of cyclic AMP in hippocampal slices: role of extracellular chloride.

We show the involvement of chloride transport on excitatory amino acids-induced accumulation of cyclic AMP in brain slices. The stimulation of cyclic AMP formation induced by excitatory amino acids in guinea pig hippocampal slices was absolutely dependent on the presence of Cl- in the incubation medium. The apparent half-maximal concentration of chloride was about 30 to 40 mM with the maximum response at more than 60 mM. As regards to the anion selectivity for the stimulation by excitatory amino acids, Br- was fully effective as Cl-, whereas F- and SO42- were ineffective. DL-(+/-)-2-Amino-4-phosphonobutyric acid, an antagonist of excitatory amino acid receptors, reduced significantly the response to excitatory amino acids. In the Cl- -free medium, the stimulatory effects of 50 microM veratridine, 10 microM forskolin and 100 microM histamine were reduced markedly but still significantly observed. The anion exchange blockers at the concentrations of more than 1 mM reduced significantly the cyclic AMP formation induced by an excitatory amino acid in a dose-dependent manner. Furosemide at the concentration of 3 mM negated the Cl- -dependent responses to forskolin and histamine without affecting the Cl- -independent ones. Furosemide did not inhibit the adenylate cyclase activity of hippocampal synaptic membrane fractions.