Endogenous Hydrogen Peroxide Regulates the Excitability of Midbrain Dopamine Neurons via ATP-Sensitive Potassium Channels

Abstract

ATP-sensitive K+(KATP) channels link metabolic state to cell excitability. Here, we examined regulation of KATPchannels in substantia nigra dopamine neurons by hydrogen peroxide (H2O2), which is produced in all cells during aerobic metabolism. Blockade of KATPchannels by glibenclamide (100 nm) or depletion of intracellular H2O2by including catalase, a peroxidase enzyme, in the patch pipette increased the spontaneous firing rate of all dopamine neurons tested in guinea pig midbrain slices. Using fluorescence imaging with dichlorofluorescein to visualize intracellular H2O2, we found that moderate increases in H2O2during partial inhibition of glutathione (GSH) peroxidase by mercaptosuccinate (0.1-0.3 mm) had no effect on dopamine neuron firing rate. However, with greater GSH inhibition (1 mmmercaptosuccinate) or application of exogenous H2O2, 50% of recorded cells showed KATPchannel-dependent hyperpolarization. Responsive cells also hyperpolarized with diazoxide, a selective opener for KATPchannels containing sulfonylurea receptor SUR1 subunits, but not with cromakalim, a selective opener for SUR2-based channels, indicating that SUR1-based KATPchannels conveyed enhanced sensitivity to elevated H2O2. In contrast, when endogenous H2O2levels were increased after inhibition of catalase, the predominant peroxidase in the substantia nigra, with 3-amino-1,2,4-triazole (1 mm), all dopamine neurons responded with glibenclamide-reversible hyperpolarization. Fluorescence imaging of H2O2indicated that catalase inhibition rapidly amplified intracellular H2O2, whereas inhibition of GSH peroxidase, a predominantly glial enzyme, caused a slower, smaller increase, especially in nonresponsive cells. Thus, endogenous H2O2modulates neuronal activity via KATPchannel opening, thereby enhancing the reciprocal relationship between metabolism and excitability.

Somatodendritic dopamine release: recent mechanistic insights

“…Further distinctions are seen in expression of ATPsensitive potassium (K ATP ) channels, which contribute to the greater effect of DA-selective neurotoxins on SNc versus VTA DA neurons [104]. Moreover, differences in K ATP channel subtypes between two populations of DA neurons within SNc contribute to the relative responsiveness of these cells to metabolic stress and to H 2 O 2 [105,106]. Differences in Ca 2þ channel expression among DA neuron populations is also well recognized, with a greater role for Cav1.3 L-type Ca 2þ channels in the regulation of pacemaker activity in SNc versus VTA DA neurons that contributes to the greater vulnerability of SNc cells to degeneration [107].…”

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“…Elevated hydrogen peroxide suppresses striatal dopamine release (Avshalumov et al 2005), and excess O&NS is involved in the degeneration of dopaminergic neurons (Tsang and Chung 2009).…”

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“…21 It can also be amplified by irreversible inhibition of peroxidase enzymes, and can lead to K ATP channel opening and suppression of axonal DA release. 22 Furthermore, in vivo studies investigating acute exposure to rotenone have shown increased generation of ROS during DA metabolism in nigrostriatal neurons. 21 32 In this work, the carbon-fiber electrode was positioned in the dorsal striatum of an anesthetized rat and ramped from −0.4 to 1.4 V in a triangular waveform every 100 ms at a scan rate of 400 V/s.…”