Molecular identification of a component of delayed rectifier current in gastrointestinal smooth muscles

Abstract

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 μM) and was insensitive to charybdotoxin. Low concentrations of quinine (1 μM) 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.

Differential Expression of Voltage-Gated K + Channel Genes in Arteries From Spontaneously Hypertensive and Wistar-Kyoto Rats

“…Several members of the Shaker family, including Kv1.1, Kv1.2, and Kv1.5, have previously been reported to be expressed in smooth muscle from vascular, 19,23,32 gastrointestinal, 21,22,33 and airway sources. 20 Yuan et al 10 have reported decreased expression of the Kv1.5 gene (but not Kv␤1.1) in pulmonary arteries of human subjects with primary pulmonary hypertension.…”

Voltage-Gated K+ Channel Dysfunction in Myocytes from a Dog Model of Subarachnoid Hemorrhage

“…Primers and the probe for Kv2.2 were based on the dog sequence of Kv2.2 (Schmalz et al, 1998) and were what we used before on dog basilar arteries with endothelium (Aihara et al, 2004 (Aihara et al, 2004). Expression levels of target genes were evaluated by the ratio of the threshold cycle (C T ) number of target mRNA to 18S rRNA.…”

Molecular and functional characterization of Kv7 K+ channel in murine gastrointestinal smooth muscles

“…Much is now known about the ionic conductances responsible for the formation of electric slow waves and the maintenance of the resting membrane potential of smooth muscle and ICC (2, 14, 30, 37, 40 -42). However, there is still a lack of information about the fundamental K ϩ channels suppressing gastrointestinal smooth muscle (GISM) contractility although K v 1.2/K v 1.5 [4-aminopyridine (4-AP) sensitive] and K v 2 [tetraethylammonium (TEA) sensitive] contribute significantly to delayed rectifier K ϩ currents (5,13,24,25,29,33). Recently, K ϩ channels encoded by KCNQ genes have been identified as major regulators of vascular contractility (4,10,16,18,23,50).…”