Na(+)- and Cl(-)-dependent [3H]GABA binding to catfish brain particles.
The uptake of [3H]GABA by homogenates of catfish brain was previously shown to be temperature-sensitive and sodium-dependent, and to display saturation kinetics. The present study is a continuation of this work and was undertaken to characterize the initial binding of [3H]GABA to its transport system. [3H]GABA binding to catfish brain particles at 4 degrees C displayed saturability and was totally dependent on both Na+ and Cl-, the optimum concentrations of which were 150 mM and 75 mM, respectively. The effects of a number of drugs on binding were established. Unlabelled GABA was the most potent inhibitor (IC50 = 3.2 microM). The structural analogues nipecotic acid and guvacine were also strongly inhibitory. Interestingly, verapamil, a Ca2+ channel blocker, also inhibited [3H]GABA binding (IC50 = 38 microM). Harmaline, known to compete for Na+ binding in other transport systems, did not appear to influence Na+ binding but was effective at displacing [3H]GABA. These results suggest that the interaction of GABA with its carrier is similar to that found in the mammalian nervous system and is further evidence that GABA is involved in neurotransmission in catfish brain.
King
S M
SM
Laboratory of Neurochemistry, Indiana University School of Medicine, Evansville 47712.
Tunnicliff
G
G
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002397:Catfishes; D002712:Chlorides / Q000494:pharmacology*; D018756:GABA Antagonists; D006246:Harmaline / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology*; D013997:Time Factors; D014700:Verapamil / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D002712:Chlorides; D018756:GABA Antagonists; D005680:gamma-Aminobutyric Acid; D012964:Sodium; D014700:Verapamil; D006246:Harmaline