Growth cones isolated from developing rat forebrain: Uptake and release of GABA and noradrenaline

Abstract

A growth cone-enriched fraction isolated from neonatal rat forebrain was shown to accumulate γ-amino[ 3H]butyric acid ([ 3H]GABA) and [ 3H]noradrenaline ([ 3H]NA). Uptake of both neurotransmitters was sodium- and temperature-dependent and exhibited saturation kinetics with K m values of 17.7 μM and 4.5 μM respectively and V max values of 114 pmol/min/mg protein and 59 pmol/min/mg protein respectively. Electron microscopic autoradiography showed that about 50% of isolated growth cones can accumulate [ 3H]GABA. Inhibitor studies showed that β-alanine was a relatively weak inhibitor of [ 3H]GABA uptake compared to nipecotic acid and diamino-butyric acid. Growth cone fractions preloaded with [ 3H]GABA and [ 3H]NA demonstrated a K + (25 mM) -induced release of both neurotransmitters. Of the K +-stimulated release of [ 3H]GABA 50% was Ca 2+-dependent, whereas the release of [ 3H]NA was entirely Ca 2+-independent.