TY - JOUR
T1 - Iptakalim modulates ATP-sensitive K+ channels in dopamine neurons from rat substantia nigra pars compacta
AU - Wu, Jie
AU - Hu, Jun
AU - Chen, Yu Ping
AU - Takeo, Teruko
AU - Suga, Sechiko
AU - DeChon, Jamie
AU - Liu, Qiang
AU - Yang, Ke Chun
AU - St. John, Paul A.
AU - Hu, Gang
AU - Wang, Hai
AU - Wakui, Makoto
PY - 2006
Y1 - 2006
N2 - Iptakalim, a novel cardiovascular ATP-sensitive K+ (K ATP) channel opener, exerts neuroprotective effects on dopaminergic (DA) neurons against metabolic stress-induced neurotoxicity, but the mechanisms are largely unknown. Here, we examined the effects of iptakalim on functional KATP channels in the plasma membrane (pm) and mitochondrial membrane using patch-clamp and fluorescence-imaging techniques. In identified DA neurons acutely dissociated from rat substantia nigra pars compacta (SNc), both the mitochondrial metabolic inhibitor rotenone and the sulfonylurea receptor subtype (SUR) 1-selective KATP channel opener (KCO) diazoxide induced neuronal hyperpolarization and abolished action potential firing, but the SUR2B-selective KCO cromakalim exerted little effect, suggesting that functional KATP channels in rat SNc DA neurons are mainly composed of SUR1. Immunocytochemical staining showed a SUR1- rather than a SUR2B-positive reaction in most dissociated DA neurons. At concentrations between 3 and 300 μM, iptakalim failed to hyperpolarize DA neurons; however, 300 μM iptakalim increased neuronal firing. In addition, iptakalim restored DA neuronal firing during rotenone-induced hyperpolarization and suppressed rotenone-induced outward current, suggesting that high concentrations of iptakalim close neuronal KATP channels. Furthermore, in human embryonic kidney 293 cells, iptakalim (300-500 μM) closed diazoxide-induced Kir6.2/SUR1 KATP channels, which were heterologously expressed. In rhodamine-123-preloaded DA neurons, iptakalim neither depolarized mitochondrial membrane nor prevented rotenone-induced mitochondrial depolarization. These data indicate that iptakalim is not a KATP channel opener in rat SNc DA neurons; instead, iptakalim is a pm-KATP channel closer at high concentrations. These effects of iptakalim stimulate further pharmacological investigation and the development of possible therapeutic applications.
AB - Iptakalim, a novel cardiovascular ATP-sensitive K+ (K ATP) channel opener, exerts neuroprotective effects on dopaminergic (DA) neurons against metabolic stress-induced neurotoxicity, but the mechanisms are largely unknown. Here, we examined the effects of iptakalim on functional KATP channels in the plasma membrane (pm) and mitochondrial membrane using patch-clamp and fluorescence-imaging techniques. In identified DA neurons acutely dissociated from rat substantia nigra pars compacta (SNc), both the mitochondrial metabolic inhibitor rotenone and the sulfonylurea receptor subtype (SUR) 1-selective KATP channel opener (KCO) diazoxide induced neuronal hyperpolarization and abolished action potential firing, but the SUR2B-selective KCO cromakalim exerted little effect, suggesting that functional KATP channels in rat SNc DA neurons are mainly composed of SUR1. Immunocytochemical staining showed a SUR1- rather than a SUR2B-positive reaction in most dissociated DA neurons. At concentrations between 3 and 300 μM, iptakalim failed to hyperpolarize DA neurons; however, 300 μM iptakalim increased neuronal firing. In addition, iptakalim restored DA neuronal firing during rotenone-induced hyperpolarization and suppressed rotenone-induced outward current, suggesting that high concentrations of iptakalim close neuronal KATP channels. Furthermore, in human embryonic kidney 293 cells, iptakalim (300-500 μM) closed diazoxide-induced Kir6.2/SUR1 KATP channels, which were heterologously expressed. In rhodamine-123-preloaded DA neurons, iptakalim neither depolarized mitochondrial membrane nor prevented rotenone-induced mitochondrial depolarization. These data indicate that iptakalim is not a KATP channel opener in rat SNc DA neurons; instead, iptakalim is a pm-KATP channel closer at high concentrations. These effects of iptakalim stimulate further pharmacological investigation and the development of possible therapeutic applications.
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U2 - 10.1124/jpet.106.106286
DO - 10.1124/jpet.106.106286
M3 - Article
C2 - 16837559
AN - SCOPUS:33749020320
SN - 0022-3565
VL - 319
SP - 155
EP - 164
JO - Journal of Pharmacology and Experimental Therapeutics
JF - Journal of Pharmacology and Experimental Therapeutics
IS - 1
ER -