Kir2.1 encodes the inward rectifier potassium channel in rat arterial smooth muscle cells

• Published in: The Journal of physiology 1999-03, Vol.515 (3), p.639-651
• Main Authors: Bradley, Karri K., Jaggar, Jonathan H., Bonev, Adrian D., Heppner, Thomas J., Flynn, Elaine R.M., Nelson, Mark T., Horowitz, Burton
• Format: Article
• Language: English
• Subjects: Animals; Barium - pharmacology; Basilar Artery - metabolism; Cesium - pharmacology; Cloning, Molecular; Coronary Vessels - metabolism; Membrane Potentials - drug effects; Mesenteric Arteries - metabolism; Muscle, Smooth, Vascular - metabolism; Oocytes - physiology; Original; Patch-Clamp Techniques; Potassium - pharmacology; Potassium Channels - drug effects; Potassium Channels - genetics; Potassium Channels - physiology; Potassium Channels, Inwardly Rectifying; Rats; Rats, Sprague-Dawley; Recombinant Proteins - metabolism; Reverse Transcriptase Polymerase Chain Reaction; Transcription, Genetic; Xenopus laevis
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1111/j.1469-7793.1999.639ab.x

The molecular nature of the strong inward rectifier K + channel in vascular smooth muscle was explored by using isolated cell RT-PCR, cDNA cloning and expression techniques. RT-PCR of RNA from single smooth muscle cells of rat cerebral (basilar), coronary and mesenteric arteries revealed transcripts for K ir 2.1. Transcripts for K ir 2.2 and K ir 2.3 were not found. Quantitative PCR analysis revealed significant differences in transcript levels of K ir 2.1 between the different vascular preparations ( n = 3; P < 0.05). A two-fold difference was detected between K ir 2.1 mRNA and β-actin mRNA in coronary arteries when compared with relative levels measured in mesenteric and basilar preparations. K ir 2.1 was cloned from rat mesenteric vascular smooth muscle cells and expressed in Xenopus oocytes. Currents were strongly inwardly rectifying and selective for K + . The effect of extracellular Ba 2+ , Ca 2+ , Mg 2+ and Cs 2+ ions on cloned K ir 2.1 channels expressed in Xenopus oocytes was examined. Ba 2+ and Cs + block were steeply voltage dependent, whereas block by external Ca 2+ and Mg 2+ exhibited little voltage dependence. The apparent half-block constants and voltage dependences for Ba 2+ , Cs + , Ca 2+ and Mg 2+ were very similar for inward rectifier K + currents from native cells and cloned K ir 2.1 channels expressed in oocytes. Molecular studies demonstrate that K ir 2.1 is the only member of the K ir 2 channel subfamily present in vascular arterial smooth muscle cells. Expression of cloned K ir 2.1 in Xenopus oocytes resulted in inward rectifier K + currents that strongly resemble those that are observed in native vascular arterial smooth muscle cells. We conclude that K ir 2.1 encodes for inward rectifier K + channels in arterial smooth muscle.