Huamin Wang, Hubert Zajicek, Vijay Kumar, Paul Wilson, and Moshe Levi

Department of Medicine, The University of Texas Southwestern Medical Center at Dallas and Department of Veterans Affairs Medical Center, Dallas, Texas 75216, USA

Received 1/13/97; Accepted 1/13/97; On-line 02/01/96

2. INTRODUCTION

Lipids play an essential structural role as a barrier between intra and extracellular medium and as a matrix providing a suitable hydrophobic environment for membrane proteins. The functional role of lipids as a selective barrier to fully or moderately water soluble compounds, and as modulators of membrane transport proteins, enzymes, and channels activity have been well recognized (1-4).

In this report we will discuss the evidence that has been obtained during the past decade which indicates an important role for alterations in renal proximal tubular cell membrane cholesterol content in the regulation of renal phosphate transport activity.

The kidney plays a critical role in the regulation of inorganic phosphate (Pi) homeostasis. Pi is freely filtered across the glomerules, and most of the Pi is reabsorbed along the proximal tubule via a sodium gradient-dependent process (Na/Pi co-transport). The Na/Pi cotransporter is located on the apical brush border membrane (BBM) of the proximal tubule. The evidence, to date, indicates that regulation of the overall renal tubular Pi transport by dietary, hormonal, or metabolic factors occurs at the level of the proximal tubular BBM Na/Pi cotransport system (5-8).