Cloning and characterization of a novel human inwardly rectifying potassium channel predominantly expressed in small intestine

Abstract

A new member of the two transmembrane domain potassium (K + ) channel family was identified and isolated from a human brain cDNA library. The cDNA clone contains an open reading frame which encodes a 360 amino acid sequence with a characteristic P domain flanked by two hydrophobic regions representing the membrane spanning segments. The closest homologue of this gene product is the inwardly rectifying potassium channel subunit, Kir1.2 (identity approximately 42%). Northern blot analysis of human tissues with a selective cDNA probe for this new K + subunit showed a single major transcript of 3.4 kb predominantly expressed at high levels in small intestine, with lower levels in stomach, kidney and brain. The main regions of expression in the central nervous system were medulla, hippocampus and corpus callosum. cRNA-injected oocytes and transiently transfected HEK293 cells expressed a K + conductance which displays an inward rectification. This conductance is blocked by cesium and barium but is insensitive to tolbutamide and diazoxide even upon co-transfection of this novel subunit with the plasmid encoding the sulfonylurea receptor SUR1. Taken together, these results demonstrate that we have isolated and characterized a novel K + channel subunit belonging to the inwardly rectifying K + (Kir) channel family to which, upon homology classification, we have given the nomenclature Kir7.1.z 1998 Federation of European Biochemical Societies.

Gastric parietal cell secretory membrane contains PKA- and acid-activated Kir2.1 K+channels

“…To investigate the molecular nature of the gastric K ϩ channel, we screened gastric mRNA by RT-PCR for three different K ϩ channels: Kir2.1 (1,30,39,44), 4.1 (2, 58), and 7.1 (33,43), which appeared to have one or more characteristics similar to those of native gastric vesicles. Primers were designed to be isoform specific, and ␤-actin was used as a control for the amount of cDNA used.…”

Inwardly Rectifying Potassium Channels: Their Structure, Function, and Physiological Roles

“…Kir7.1 was independently identified by three groups (140,393,604 (140, 393). The residue responsible for these unusual characteristics in the pore region is M125 (Arg in all other Kir subunits).…”

Focus on Kir7.1: physiology and channelopathy

“…It was independently identified by 3 groups in the secretory epithelial cells of the choroid plexus, 27 central neuron cells 28 and in the small intestine. 29 The primary structure of K ir channels consists a common motif of 2 membrane spanning domains (TM1 and TM2) linked by an extracellular pore forming region (H5) and cytoplasmic amino (NH 2 -) and carboxy (COOH-) terminal domains. This topology is common to all K ir channels.…”