Phospholemman expression in extraglomerular mesangium and afferent arteriole of the juxtaglomerular apparatus

Abstract

The molecular mechanisms with which the juxtaglomerular apparatus accomplishes its twin functions, acute regulation of glomerular blood flow and secretion of renin, are still not clearly understood. Least understood is the role of the extraglomerular mesangial (EM) cells, also known as lacis or Goormaghtigh cells, which lie sandwiched between the macula densa and the afferent and efferent arterioles. Here, we report that immunoreactivity for phospholemman (FXYD1), a single-span membrane protein homologous to the gamma (γ) sub-unit of the Na,K-ATPase, is found in the kidney in EM cells with the Na,K-ATPase β2-subunit and in cortical blood vessels and the afferent arteriole with Na,K-ATPase α2 and β2. Phospholemman's distribution in EM cells is distinct from that of the Na,K-ATPase γ-subunit, which is found on the basolateral surface of macula densa cells with Na,K-ATPase α1 and β1. Phospholemman is a major kinase target, and its location in the juxtaglomerular apparatus suggests that it is involved in tubuloglomerular feedback.