Expression of a functional Kir4 family inward rectifier K⁺ channel from a gene cloned from mouse liver

Abstract

A low stringency polymerase chain reaction (PCR) homology screening procedure was used to probe a mouse liver cDNA library to identify novel inward rectifier K+ channel genes. A single gene (mLV1) was identified that exhibited extensive sequence homology with previously cloned inward rectifier K+ channel genes. The mLV1 gene showed greatest sequence identity with genes belonging to the Kir4 subfamily. The amino acid sequence of mLV1 was 96 % identical to a Kir channel cloned from human kidney (hKir4.2), and ≈60 % identical to the Kir4.1 channel cloned from human and rat, so that mLV1 was classified as mKir4.2. Xenopus oocytes injected with cRNA encoding mKir4.2 displayed a large inwardly rectifying K+ current, while control oocytes injected with H2O displayed no similar K+ current. The current was blocked by Ba2+ and Cs+ in a voltage‐dependent fashion and displayed inward rectification that was intermediate between that of the strong inward rectifier Kir2.1 and the weak inward rectifier Kir1.1. The current was weakly blocked by TEA in a voltage‐independent fashion. mKir4.2 current was subject to modulation by several distinct mechanisms. Intracellular acidification decreased mKir4.2 current in a reversible fashion, while activation of protein kinase C decreased mKir4.2 current in a manner that was not rapidly reversible. Incubation of oocytes in elevated [K+] produced a slowly developing enhancement of current. Oocytes co‐injected with cRNA for mKir4.2 and Kir5.1, a protein that does not form functional homomeric channels, displayed membrane currents with properties distinct from those expressing mKir4.2 alone. Co‐injected oocytes displayed larger currents than mKir4.2, with novel kinetic properties and an increased sensitivity to Ba2+ block at negative potentials, suggesting that mKir4.2 forms functional heteromultimeric channels with Kir5.1, as has been shown for Kir4.1 These results demonstrate for the first time that a Kir4.2 channel gene product forms functional channels in Xenopus oocytes, that these Kir channels display novel properties, and that Kir4.2 subunits may be responsible for physiological modulation of functional Kir channels.

The α9β1 integrin enhances cell migration by polyamine-mediated modulation of an inward-rectifier potassium channel

“…Our studies identify the involvement of one Kir channel subunit, Kir4.2, downstream of the ␣9 integrin in a pathway that enhances cell migration. Kir4.2 is present in a wide variety of tissues, including lung and liver, that are also sites of expression of the ␣9 integrin subunit (48,49). Thus, it remains plausible that these proteins functionally cooperate in vivo.…”

Expression of inwardly rectifying potassium channel subunits in native human retinal pigment epithelium

“…3f). Kir4.2, which has been reported to have a molecular mass of ~35 kDa to 40 kDa (Ferrando-Miguel et al, 2004;Hill et al, 2002), possesses a glycosylation motif (Pearson et al, 1999;Shuck et al, 1997). Thus, the two bands in brain and retina may represent unglycosylated and glycosylated dimers (Hibino et al, 2004).…”

“…Kir4.2 subunits form K + channels with intermediate inward rectification and can co-assemble with Kir5.1 subunits, which influence its rectification and gating properties (Pearson et al, 1999). Unlike Kir4.1 channels, Kir4.2 channels expressed in mammalian cells are insensitive to intracellular pH within the physiological range (Lam et al, 2006).…”

An Inwardly Rectifying Potassium Channel in Apical Membrane of Calu-3 Cells

“…Block by external Cs ϩ was highly voltage sensitive, and required Ͼ20 mM at Ϫ80 mV. No other studies have been reported for human Kir4.2, but in mouse Kir4.2, Cs ϩ blocks in the 100 M (ϳϪ120 mV) range (13). Kir channels display a broad range of sensitivities to Cs ϩ block, with K d values ranging over a 100-fold range near resting membrane potentials.…”

“…Kir channels display a broad range of sensitivities to Cs ϩ block, with K d values ranging over a 100-fold range near resting membrane potentials. Kir channels with micromolar sensitivity to external Cs ϩ include hKir2.1 at Ϫ92 mV (28), hamKir2.1 at ϳϪ80 mV (29), mKir3.2 at ϳϪ90 mV (30), rat Kir4.1 at ϳϪ75 mV (31), and mKir4.2 at ϳϪ120 mV (13). Kir channels with millimolar sensitivity to Cs ϩ block include Kir1.1 at Ϫ80 mV (32), Kir2.1 at ϳϪ110 mV (17), Kir2.4 at ϳϪ80 mV (33), and hKir7.1 at ϳϪ60 mV (34).…”