Activation of ATP-sensitive K+ (K(ATP)) channels by H2O2 underlies glutamate-dependent inhibition of striatal dopamine release

Abstract

In many cells, ATP-sensitive K+ channels (KATP channels) couple metabolic state to excitability. In pancreatic beta cells, for example, this coupling regulates insulin release. Although KATP channels are abundantly expressed in the brain, their physiological role and the factors that regulate them are poorly understood. One potential regulator is H2O2. We reported previously that dopamine (DA) release in the striatum is modulated by endogenous H2O2, generated downstream from glutamatergic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-receptor activation. Here we investigated whether H2O2-sensitive KATP channels contribute to DA-release modulation by glutamate and gamma-aminobutyric acid (GABA). This question is important because DA-glutamate interactions underlie brain functions, including motor control and cognition. Synaptic DA release was evoked by using local electrical stimulation in slices of guinea pig striatum and monitored in real time with carbon-fiber microelectrodes and fast-scan cyclic voltammetry. The KATP-channel antagonist glibenclamide abolished the H2O2-dependent increase in DA release usually seen with AMPA-receptor blockade by GYKI-52466 [1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride] and the decrease in DA release seen with GABA-type-A-receptor blockade by picrotoxin. In contrast, 5-hydroxydecanoate, a mitochondrial KATP-channel blocker, was ineffective, as were sulpiride, a D2-receptor antagonist, and tertiapin, a G protein-coupled K+-channel inhibitor. Diazoxide, a sulfonylurea receptor 1 (SUR1)selective KATP-channel opener, prevented DA modulation by H2O2, glutamate, and GABA, whereas cromakalim, a SUR2-selective opener, did not. Thus, endogenous H2O2 activates SUR1-containing KATP channels in the plasma membrane to inhibit DA release. These data not only demonstrate that KATP channels can modulate CNS transmitter release in response to fast-synaptic transmission but also introduce H2O2 as a KATP-channel regulator.

Fig. 1.

Glutamate–H₂O₂-dependent modulation of striatal DA release is blocked by glibenclamide. (A) Glibenclamide (Glib; 3 μM) caused a significant increase in evoked DA release (P < 0.01, glibenclamide vs. control; n = 5). (B) Applied voltage waveform and representative voltammograms of DA obtained during DA calibration (DA cal; 1 μM) and at maximum evoked [DA]_o during stimulation (10 Hz, 30 pulses) in normal aCSF (control) and in the presence of glibenclamide in the same striatal slice. Sampling interval was 100 ms; voltage scan rate was 800 V/s. (C) In the presence of glibenclamide, the usual effects of MCS (1 mM), GYKI-52466 (GYKI; 50 μM), and picrotoxin (100 μM) on DA release were prevented (P > 0.05, each agent vs. glibenclamide alone; n = 5). Data are given as mean ± SEM, illustrated as percentage of same-site control. Solid bars indicate the stimulation period.

Fig. 2.

Glutamate–H₂O₂-dependent inhibition of striatal DA release does not involve D₂ receptors or G protein-coupled K⁺ channels. (A) Sulpiride (1 μM), a D₂-receptor antagonist, increased evoked [DA]_o in striatum (P < 0.001, sulpiride vs. control; n = 6). The usual suppression of pulse-train-evoked DA release seen in MCS (1 mM) persisted in the presence of sulpiride (P < 0.001, sulpiride plus MCS vs. sulpiride; n = 6). (B) Blockade of G protein-coupled K⁺ channels with tertiapin (100 nM to 1 μM) caused a significant increase in striatal DA release (P < 0.001, tertiapin vs. control; n = 7) but did not alter the usual increase in evoked [DA]_o seen with AMPA receptor blockade by GYKI-52466 (GYKI; 50 μM) (P < 0.001, tertiapin + GYKI vs. tertiapin; n = 7). Solid bars indicate the stimulation period.

Fig. 3.

mitK_ATP channels do not mediate glutamate–H₂O₂-dependent modulation of striatal DA release. The mitK_ATP-channel inhibitor 5-HD (100 μM) caused an increase in evoked [DA]_o (P < 0.01, 5-HD vs. control; n = 4). However, 5-HD had no effect on the further increase in DA release that accompanied AMPA-receptor blockade by GYKI-52466 (GYKI; 50 μM) (P < 0.001, 5-HD + GYKI vs. 5-HD; n = 4). Solid bars indicate the stimulation period.

Fig. 4.

Differential effects of K_ATP-channel openers on striatal DA release. (Upper) Diazoxide (30 μM), a SUR1-selective K_ATP-channel opener, decreased evoked [DA]_o in striatum (P < 0.01, diazoxide vs. control; n = 5). Moreover, diazoxide abolished the effects of MCS, GYKI-52466 (GYKI), and picrotoxin (PTX) on DA release (P > 0.05, diazoxide + each agent vs. diazoxide; n = 5). (Lower) Cromakalim (30 μM), a SUR2-selective K_ATP-channel opener, also caused a significant decrease in evoked [DA]_o (P < 0.01, cromakalim vs. control; n = 5) but did not alter the usual pattern of DA-release modulation seen with MCS, GYKI-52466, and PTX (P < 0.05, cromakalim + each agent vs. cromakalim; n = 5). Solid bars indicate the stimulation period.