Iptakalim modulates ATP-sensitive K(+) channels in dopamine neurons from rat substantia nigra pars compacta.
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 K(ATP) 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 K(ATP) channel opener (KCO) diazoxide induced neuronal hyperpolarization and abolished action potential firing, but the SUR2B-selective KCO cromakalim exerted little effect, suggesting that functional K(ATP) 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 microM, iptakalim failed to hyperpolarize DA neurons; however, 300 microM 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 K(ATP) channels. Furthermore, in human embryonic kidney 293 cells, iptakalim (300-500 microM) closed diazoxide-induced Kir6.2/SUR1 K(ATP) 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 K(ATP) channel opener in rat SNc DA neurons; instead, iptakalim is a pm-K(ATP) channel closer at high concentrations. These effects of iptakalim stimulate further pharmacological investigation and the development of possible therapeutic applications.
Wu
Jie
J
Neurophysiology Laboratory, Neurology Research, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ 85013-4496, USA. Jie.Wu@chw.edu
Hu
Jun
J
Chen
Yu-Ping
YP
Takeo
Teruko
T
Suga
Sechiko
S
Dechon
Jamie
J
Liu
Qiang
Q
Yang
Ke-Chun
KC
St John
Paul A
PA
Hu
Gang
G
Wang
Hai
H
Wakui
Makoto
M
D018528:ATP-Binding Cassette Transporters / Q000187:drug effects; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects*; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects; D011437:Propylamines / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D011955:Receptors, Drug; D012402:Rotenone / Q000494:pharmacology; D013378:Substantia Nigra / Q000187:drug effects*; D064233:Sulfonylurea Receptors; D014044:Tolbutamide / Q000494:pharmacology; D000099161:Kcnj11 Channel
D018528:ATP-Binding Cassette Transporters; D000255:Adenosine Triphosphate; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011437:Propylamines; D011955:Receptors, Drug; D012402:Rotenone; D064233:Sulfonylurea Receptors; D014044:Tolbutamide; D000099161:Kcnj11 Channel; C577507:ABCC8 protein, human; C577509:Abcc8 protein, rat; C502260:N-(1-methylethyl)-1,1,2-trimethylpropylamine; C117780:mitochondrial K(ATP) channel