GABA transport in the rat thyroid.
1. The uptake of gamma-aminobutyric acid (GABA) into rat thyroid slices was studied. 2. Uptake of 14C-GABA was concentration-dependent: one unsaturable (diffusion) and two saturable components obeying Michaelis-Menten kinetics contributed to transport. 3. The kinetic constants of saturable GABA transport systems were: Km1 = 1.5 microM, V1 = 4.0 nmol x (g wet weight)-1 x (20 min)-1 (high-affinity uptake): Km2 = 800 microM, V2 = 260 nmol x (g wet weight)-1 x (20 min)-1 (low-affinity uptake). 4. Uptake mediated by each of the carrier systems was concentrative, entirely Na+-dependent, and required activation energies characteristic for active transport. 5. High-affinity transport was structurally specific for GABA. The substrate specificity of low-affinity uptake resembled that of beta-amino acid transport systems.
D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D001692:Biological Transport; D018756:GABA Antagonists; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000502:physiology; D013696:Temperature; D013961:Thyroid Gland / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D000596:Amino Acids; D000963:Antimetabolites; D018756:GABA Antagonists; D005680:gamma-Aminobutyric Acid; D012964:Sodium