Molecular identification of a component of delayed rectifier current in gastrointestinal smooth muscles.
Kv2.2, homologous to the shab family of Drosophila voltage-gated K+ channels, was isolated from human and canine colonic circular smooth muscle-derived mRNA. Northern hybridization analysis performed on RNA prepared from tissues and RT-PCR performed on RNA isolated from dispersed and selected smooth muscle cells demonstrate that Kv2.2 is expressed in smooth muscle cells found in all regions of the canine gastrointestinal (GI) tract and in several vascular tissues. Injection of Kv2.2 mRNA into Xenopus oocytes resulted in the expression of a slowly activating K+ current (time to half maximum current, 97 +/- 8.6 ms) mediated by 15 pS (symmetrical K+) single channels. The current was inhibited by tetraethylammonium (IC50 = 2.6 mM), 4-aminopyridine (IC50 = 1.5 mM at +20 mV), and quinine (IC50 = 13.7 microM) and was insensitive to charybdotoxin. Low concentrations of quinine (1 microM) were used to preferentially block the slow component of the delayed rectifier current in native colonic myocytes. These data suggest that Kv2.2 may contribute to this current in native GI smooth muscle cells.
Schmalz
F
F
Department of Physiology, School of Medicine, University of Nevada, Reno 89557, USA.
Kinsella
J
J
Koh
S D
SD
Vogalis
F
F
Schneider
A
A
Flynn
E R
ER
Kenyon
J L
JL
Horowitz
B
B
D015761:4-Aminopyridine / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D015152:Blotting, Northern; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D051668:Delayed Rectifier Potassium Channels; D004064:Digestive System / Q000166:cytology; D004068:Digestive System Physiological Phenomena; D004285:Dogs; D004553:Electric Conductivity; D006801:Humans; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000166:cytology / Q000502:physiology*; D009865:Oocytes / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated; D051669:Shab Potassium Channels; D019789:Tetraethylammonium / Q000494:pharmacology; D014981:Xenopus
D018076:DNA, Complementary; D051668:Delayed Rectifier Potassium Channels; C496992:KCNB2 protein, human; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D051669:Shab Potassium Channels; D019789:Tetraethylammonium; D004247:DNA; D015761:4-Aminopyridine