Localization of the sulphonylurea receptor subunits, SUR2A and SUR2B, in rat renal tubular epithelium.

摘要

ATP-sensitive K+ (K(ATP)) channels in the kidney are considered to play roles in regulating membrane potential according to changes in the intracellular ATP concentration. They are composed of two types of subunits; the pore subunits (Kir6.1, Kir6.2), which are members of the inwardly rectifying K+ channel family, and the regulatory subunits, the sulphonylurea receptors, which belong to the ATP-binding cassette (ABC) superfamily. The sulphonylurea receptors (SURs) are receptors of sulphonylureas widely used for the treatment of type 2 diabetes mellitus. The SURs are divided into two isoforms, SUR1 and SUR2, the latter was further divided into SUR2A and SUR2B. In the present study, we have investigated the mRNA expression by RT-PCR assay, and protein expression profiles by immunoblotting, immunohistochemistry, and immunoelectron microscopy with anti SUR2A and anti SUR2B antibodies. RT-PCR detected the presence of mRNA transcripts of the SUR2A and SUR2B, while SUR1 mRNA was barely detected. In immunoblotting, SUR2A protein was detected distinctly in the microsomal fraction, weakly in the mitochondrial fraction and at negligible level in the cell membrane fraction. In contrast, the SUR2B protein was detected intensely in the microsomal fraction, with a low level in the mitochondrial fraction and scarcely in the cell membrane fraction. In immunohistochemistry SUR2A and SUR2B proteins were widely distributed in renal tubular epithelial cells, glomerular mesangial cells, and the endothelium and the smooth muscle of blood vessels. In immunoelectron microscopy, the immunoreactivity was localized in the endoplasmic reticulum and mitochondria throughout the epithelial cells for SUR2A, and dominantly in the apical cytoplasm of the cells for SUR2B. In conclusion, the regulatory subunits of the K(ATP) channel in the rat kidney are SUR2A and SUR2B; they also are candidate regulatory subunits for the mitochondrial K(ATP) channel.