Effects of lead salts on the uptake, release, and binding of gamma-aminobutyric acid: the importance of buffer composition.

The effects of lead on the uptake and release of gamma-[3H]aminobutyric acid [( 3H]GABA) from rat brain slices were examined in solutions buffered with Tris-HCl, sodium phosphate, and sodium bicarbonate. Lead acetate (10-250 microM) inhibited uptake and potassium-stimulated release and facilitated spontaneous efflux only in solutions buffered with Tris-HCl. Calcium-independent binding of [3H]GABA was unaffected by lead acetate (1-100 microM) in Tris-citrate buffer but was significantly inhibited by 3 microM lead acetate in Tris-HCl solution. At the rat soleus neuromuscular junction, lead caused a dose-dependent reduction of end-plate potential amplitude at concentrations of 10-100 microM lead acetate in HEPES-buffered solution but had no effect at these concentrations in phosphate-buffered solution. Stability constants of lead complexes indicate that buffers containing carbonate and phosphate are unlikely to contain a significant concentration of Pb2+, as complexing by these anions would reduce the availability of free Pb2+. This study indicates that the choice of buffer is important when investigating the effects of lead on biological systems and that negative findings may result from the use of inappropriate buffers. It also has important clinical implications suggesting that some effects of lead poisoning may result from its ability to affect neurotransmitter systems directly and that local changes in pH and complexing anion concentrations in the CNS may influence its biological availability and, hence, variable biological responses.