Expression and immunolocalization of ERG1 potassium channels in the rat kidney

Potassium (K⁺) channels participate in K⁺ secretion, K⁺ recycling, and cell volume regulation and help to maintain the resting potential in mammalian kidneys. Previously, we identified a set of voltage-gated K⁺ channels (Kv1) in the inner medullary collecting duct of the rat kidney. In the present work, we identified the voltage-gated K⁺ channel ether-à-go-go-related gene (ERG) in the rat kidney. mRNAs of ERG1a and its N-terminal splice-variant ERG1b were detected. Immunoblots of the cortex and medulla revealed two molecular mass proteins of 135 and 80 kDa, consistent in size with the nonglycosylated ERG1a and ERG1b isoforms, respectively. However, bands of 155 and 95 kDa, corresponding to mature glycosylated ERG1a and ERG1b, respectively, were also observed. In our immunohistochemical experiments, we could not differentiate the ERG1 isoforms because we used an antibody against a carboxy-terminal epitope. ERG1 was differentially localized in specific nephron segments: its localization was intracellular in the proximal tubule and medullary collecting ducts and in the apical membranes in the distal convoluted and connecting tubules. ERG1 was also abundant in glomerular arterioles and renal vessels. In summary, ERG1 displays a heterogeneous distribution in the rat kidney.