Hydrogen‐Peroxide‐Induced Toxicity of Rat Striatal Neurones Involves Activation of a Non‐Selective Cation Channel

Abstract

Striatal neurones are particularly vulnerable to hypoxia/ischaemia-induced damage, and free radicals are thought to be prime mediators of this neuronal destruction. It has been shown that hydrogen peroxide (H₂O₂), through the production of free radicals, induces rat insulinoma cell death by activation of a non-selective cation channel, which leads to irreversible cell depolarization and unregulated Ca²⁺ entry into the cell. In the study presented here, we demonstrate that a subpopulation of striatal neurones (medium spiny neurones) is depolarized by H₂O₂ through the production of free radicals. Cell-attached recordings from rat cultured striatal neurones demonstrate that exposure to H₂O₂ opens a large-conductance channel that is characterized by extremely long open times (seconds). Inside-out recordings show that cytoplasmically applied β-nicotinamide adenine dinucleotide activates a channel with little voltage dependence, a linear current-voltage relationship and a single-channel conductance of between 70 and 90 pS. This channel is permeable to Na⁺, K⁺ and Ca²⁺ ions. Fura-2 imaging from cultured striatal neurones reveals that H₂O₂ exposure induces a biphasic intracellular Ca²⁺ increase in a subpopulation of neurones, the second, later phase resulting in Ca²⁺ overload. This later component of the Ca²⁺ response is dependent on the presence of extracellular Ca²⁺ and is independent of synaptic activity or voltage-gated Ca²⁺ channel opening. Consequently, this channel may be an important contributor to free radical-induced selective striatal neurone destruction. These results are remarkably similar to those observed for insulinoma cells and suggest that this family of non-selective cation channels has a widespread distribution in mammalian tissues.