The Lipid Peroxidation Product 4-Hydroxynonenal Potently and Selectively Inhibits Synaptic Plasma Membrane Ecto-ATPase Activity,A Putative Regulator of Synaptic ATP and Adenosine

Synaptic plasma membrane (SPM)-bound, extracellular-facing (ecto) ATPases are Mg²⁺- or Ca²⁺-activated enzymes that regulate the synaptic levels of the excitatory neurotransmitter ATP and provide ADP for the further ecto-nucleotidase-mediated production of the inhibitory neuromodulator adenosine. The present results show that low concentrations (IC₅₀ = 4 M) of the lipid peroxidation product 4-hydroxynonenal (HNE) inhibited up to about 80% of the ecto-ATPase activity of SPM purified from rat brain cerebral cortex. In contrast, low concentrations of HNE did not inhibit the activity of the intracellular-facing Na⁺, K⁺, Mg²⁺-ATPase. In addition, the inhibition of SPM ecto-ATPase activity by HNE was largely irreversible and pH-dependent. Furthermore, structure-activity studies demonstrate that inhibition was dependent on the presence of the reactive functional groups of HNE. These findings suggest that HNE selectively inhibits SPM ecto-ATPase activity by a mechanism that may involve the covalent modification of functionally-critical nucleophilic amino acids. It is proposed that inhibition of SPM ecto-ATPase activity could contribute to the mechanisms by which lipid peroxidation and HNE formation promote excitotoxicity.