cAMP and forskolin decrease gamma-aminobutyric acid-gated chloride flux in rat brain synaptoneurosomes.
The effects of the cyclic nucleotide cAMP on gamma-aminobutyric acid-gated chloride channel function were investigated. The membrane-permeant cAMP analog N6,O2'-dibutyryladenosine 3',5'-cyclic monophosphate inhibited muscimol-induced 36Cl- uptake into rat cerebral cortical synaptoneurosomes in a concentration-dependent manner (IC50 = 1.3 mM). The inhibition was due to a decrease in the maximal effect of muscimol, with no change in potency. Similar effects were observed with 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate, 8-bromoadenosine 3',5'-cyclic monophosphate, and the phosphodiesterase inhibitor isobutylmethylxanthine. The effect of endogenous cAMP accumulation on the gamma-aminobutyric acid-gated Cl- channel was studied with forskolin, an activator of adenylate cyclase. Under identical conditions, in the intact synaptoneurosomes, forskolin inhibited muscimol-induced 36Cl- uptake and generated cAMP with similar potencies (IC50 = 14.3 microM; EC50 = 6.2 microM, respectively). Surprisingly, 1,9-dideoxyforskolin, which does not activate adenylate cyclase, also inhibited the muscimol response, suggesting that forskolin and its lipophilic derivatives may interact with the Cl- channel directly. Indeed, forskolin inhibition of muscimol-induced 36Cl- uptake was extremely rapid (within 5 sec), preceding the accumulation of sufficient levels of cAMP. After 5 min, a slower phase of inhibition was seen, similar to the time course for cAMP accumulation. The data suggest that gamma-aminobutyric acid (GABAA) receptor function in brain can be regulated by cAMP-dependent phosphorylation.
Heuschneider
G
G
Department of Pharmacology, Duke University Medical Center, Durham, NC 27710.
Schwartz
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RD
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000502:physiology*; D003994:Bucladesine / Q000494:pharmacology; D018118:Chloride Channels; D002712:Chlorides / Q000502:physiology*; D005576:Colforsin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000502:physiology*; D066298:In Vitro Techniques; D008565:Membrane Proteins / Q000502:physiology*; D009118:Muscimol / Q000494:pharmacology; D051381:Rats; D013574:Synaptosomes; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D018118:Chloride Channels; D002712:Chlorides; D008565:Membrane Proteins; D005576:Colforsin; D009118:Muscimol; D005680:gamma-Aminobutyric Acid; D003994:Bucladesine; D000242:Cyclic AMP; D015056:1-Methyl-3-isobutylxanthine