Evidence for a Carrier-mediated Transfer Model for the Accumulation of ¹⁴C-γ-Aminobutyric Acid by Brain Particles at Zero Degrees Centigrade

Abstract

It has been shown that subcellular particles prepared from sucrose homo-genates of imouse brain can accumulate isotopioally labeled γ-aminobuttyric acid (/ABA) when suspended in a Na⁺ containing medium (0.2 M NiaCl, 0.05 M tris-HCl pH 7.3, ¹⁴C-γABA) at 0° C. This process is Na⁺ dependent, pH dependent and osmotictally sensitive (S a n o and R o b e r t s 1963). In studies which were carried out on a morphologically heterogeneous mitochondrial fraction (containing mitochondria, synaptosomes, myelin structures and vesicular fragments of endoplasmic reticulum) and a microsomal fraction (predominantly composed of vesicular fragments of endoplasmic (reticulum) the following observations were made (Varon, Weinstein and Roberts 1964): Both preparations contained endogenous γ ABA in the particles. Upon transfer of the heterogeneous mitochondrial fraction from a sucrose medium to the radioactive ¹⁴C-γABA saline suspension, there was an initial net increment in the amount of total bound γABA, even though the isotopie evidence indicated a concurrent release into the suspending medium of endogenous γABA by the particles. This phase was followed by a slow net release of γABA. The accumulation of ¹⁴C-γABA by the particles continued during the early stages of the net loss of γABA from the particles.

This work was supported in part by grant NB-01615 from the National Institute of Neurological Diseases and Blindness, National Institutes of Health, and by a grant from the National Association for Mental Health.