4-acetamido-4--isothiocyanatostilbene-2-2--disulfonic-acid and 2-amino-4-phosphonobutyric-acid

1. Depolarizing responses to DL-2-amino-4-phosphonobutyrate (AP4) and related amino acids have been studied in the rat cerebral cortex slice following the application of quisqualate (Quis). 2. Before exposure to Quis, 500 microM DL-AP4 had little or no effect. However, following a single application of 40 microM Quis for 2 min, DL-AP4 produced depolarizing responses. With repeated applications of DL-AP4, there was a decline in response amplitude. A second application of Quis restored the depolarizing potency of DL-AP4 to a level above that for the first DL-AP4 response after the first Quis application. With a sequence of alternate applications of Quis and DL-AP4, the amplitude of DL-AP4 responses became maximal after the second Quis application. Responses to DL-AP4 could also be induced by the application of 1 microM Quis for 60 min, but were smaller in amplitude. 3. Responses to the normally inactive amino acids L-cysteine (Cys), L-cystathionine (CTN) and L-alpha-aminoadipate (AA) were also induced once Quis was applied. These responses were also maximized after a second application of Quis, except those to L-Cys, which failed to reach a plateau after three Quis applications. 4. The co-application of DL-AP4 with the first Quis application depressed the subsequent mean DL-AP4 response by 47%. Re-application of Quis restored the amplitude of DL-AP4 responses to levels comparable to control. L-alpha-AA also suppressed the induction of DL-AP4 responses, when co-applied with the first Quis exposure, reducing mean response amplitude by 98%. Unlike DL-AP4, however, the effect with L-alpha-AA persisted so that DL-AP4 responses were significantly suppressed compared to control, even after further applications of Quis. 5. The effects of the anion transport blockers, 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and 4-acetoamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid (SITS) on the induction process and the DL-AP4 responses themselves were examined. DIDS (100 microM) significantly inhibited the DL-AP4 responses, and to a lesser extent the induction of the responses by 40 microM Quis (2 min), while SITS (300 microM) only inhibited the DL-AP4 responses. However, the induction of responses by 1 microM Quis (60 min) was significantly affected by this concentration of SITS. 6. DIDS (100 microM) had no effect on responses to alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionate (AMPA), but selectively potentiated those to Quis. Examination of the ful

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Amino Acids; Aminobutyrates; Animals; Cerebral Cortex; Excitatory Amino Acid Antagonists; Ibotenic Acid; In Vitro Techniques; Male; Neuromuscular Depolarizing Agents; Quisqualic Acid; Rats; Rats, Wistar; Receptors, AMPA; Receptors, Glutamate

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.

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Aminobutyrates; Animals; Bromides; Chlorides; Colforsin; Cyclic AMP; Fluorides; Furosemide; Guinea Pigs; Hippocampus; Histamine; Male