INHIBITION OF GLUTAMATE UPTAKE AND PROTON-PUMPING IN SYNAPTIC VESICLES BY S-NITROSYLATION

Nitric oxide (NO; including NO., NO+, and NO-) was found to inhibit gl utamate uptake by isolated synaptic vesicles of rat brain. This was ob served when two unrelated NO donors, S-nitrosogluthathione and S-nitro so-N-acetylpenicillamine, were used. The primary target of NO is the H +-ATPase found in the synaptic vesicles, which leads to dissipation of the electrochemical proton gradient and inhibition of glutamate uptak e. Oxyhemoglobin (12 mu M) and, to a much lesser extent, methemoglobin protected the vacuolar H+-ATPase from inhibition. Inhibition of H+ pu mping by NO was reversed by addition of 0.5 mM dithiothreitol. The res ults indicate that the vacuolar H+-ATPase from synaptic vesicles is in hibited by NO by a mechanism that involves S-nitrosylation of critical sulfhydryl groups in the enzyme. The interaction of NO with synaptic vesicles might be of importance for the understanding of the multiple effects of NO in neurotransmission.