—β‐Bungarotoxin, a presynaptically‐acting polypeptide neurotoxin, caused an efflux from synaptosomes of previously accumulated γ‐aminobutyric acid and 2‐deoxy‐d‐glucose. The toxin‐induced efflux of γ‐aminobutyric acid occurred by a Na+ ‐dependent process while that of 2‐deoxyglucose was Na+ ‐independent. These effects were also produced by treating synaptosomes with low molecular weight compounds, including fatty acids, that inhibit oxidative phosphorylation. After incubation with β‐bungarotoxin, synaptosomes exhibited increased production of 14CO2 from [U‐14C]glucose and decreased ATP levels. β‐Bungarotoxin treatment of various subcellular membrane fractions caused the production of a factor that uncoupled oxidative phosphorylation when added to mitochondria. Mitochondria from toxin‐treated brain tissue exhibited a limitation in the maximal rate of substrate utilization. We conclude that β‐bungarotoxin acts by inhibiting oxidative phosphorylation in the mitochondria of nerve terminals. This inhibition accounts for the observed β‐bungarotoxin effects on synaptosomes and at neuromuscular junctions. We suggest that the effects on energy metabolism result from a phospholipase A activity found to be associated with the toxin.

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Na⁺-dependent, high-affinity transport of ¹⁴C-GABA into adult and neonatal (1–2 days old) crude synaptosomal fractions was measured at various temperatures in incubation media containing either high (108 mM) or low (18 mM) sodium ion concentrations. Determinations of V_max and K_m revealed a possible difference in the kinetics of GABA transport between the two maturational stages in the high (HS) and low sodium (LS) buffers. Arrhenius plots of data obtained using HS buffer were similar for both adults and neonates. In both plots there was a discontinuity between 20 and 25°C and the apparent activation energies (E_a) on either side of this transition temperature (T_c) were similar in both stages of development. Van''t Hoff plots of data obtained using HS buffer also revealed similar changes in the apparent heat content (ΔH_m) in both developmental stages. Arrhenius plots of data from LS buffer for both stages were similar to each other but not to those in HS buffer. T_c was different and the activation energies above T_c were smaller. Changes in the apparent heat content in LS buffer were also less than those in HS buffer.