Inhibition of Na+-dependent GABA uptake in isolated frog sensory nerve cell bodies by extra- and intracellular Li+.
The effect of Li+ on the Na+-dependent gamma-aminobutyric acid (GABA) uptake was investigated by examining the effects of external and internal Li+ ([Li]o and [Li]i) on GABA-gated Cl- current (ICl) in the frog dorsal root ganglion cells using the suction pipette technique which allows the internal perfusion under voltage-clamp condition. The suppression of GABA responses in the presence of external Na+ ([Na]o) was larger at lower than at higher GABA concentration. Replacement of [Na]o with Li+ completely removed the Na+ suppression, and GABA dose-response curve in Li+ external solution agreed well with that in Na+-free (Tris+) external solution. Either increasing [Li]i) or internal Na+ ([Na]i) at a constant [Na]o equally reduced the Na+-dependent suppression of GABA-gated ICl. The results indicate that both the [Li]o and [Li]i remove in different manner the [Na]o-dependent suppression of GABA-induced ICl:i.e. the [Li]o acts as a blocker of Na+-GABA co-transport mechanism while the increase of [Li]i decreases the Na+ electrochemical potential gradient across the soma membrane as well as [Na]i does.
D000818:Animals; D005727:Ganglia, Spinal / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D008094:Lithium / Q000008:administration & dosage / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D011892:Rana catesbeiana; D012964:Sodium / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D005680:gamma-Aminobutyric Acid; D008094:Lithium; D012964:Sodium