Nitric oxide-evoked [H-3]gamma-aminobutyric acid release is mediated by two distinct release mechanisms

Mechanisms underlying the release of [H-3]gamma-aminobutyric acid (GABA) evoked by nitric oxide (NO) were investigated by use of primary cultured neurons prepared from the mouse cerebral cortex. NO generators such as sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) increased both [H-3]GABA release from the neurons and [Ca-45(2+)] influx into the neurons in a dose-dependent manner, which was significantly diminished by hemoglobin. The removal of Ca2+ significantly reduced the NO-induced [H-3]GABA release by about 50%. Nipecotic acid and 1-(2-(((diphenylmethylene)amino)oxy)ethyl)-1,2,5,6-tetrahydro-3-pyridinecarboxylic acid (NO-711), GABA uptake inhibitors, dose-dependently inhibited the NO-evoked [H-3]GABA release in either the presence or absence of Ca2+. The concentration of these GABA uptake inhibitors to suppress the NO-induced release of [H-3]GABA was sufficiently lower than that to exhibit the inhibition of [H-3]GABA transport into the neurons. In addition, the NO-evoked [H-3]GABA release was reduced by approximately 50% when total Na+ in incubation buffer was replaced with equimolar choline, and was also completely abolished by the removal of both Ca2+ and Na+. These results indicate that the release of [H-3]GABA evoked by NO is mediated by two release mechanisms, a Ca2+-dependent release system and the reverse process of the Ca2+-independent and Na+-dependent carrier-mediated GABA uptake system.