Introduction

The uptake of glucose into mammalian cells is a necessity, and, regardless of the cell type, occurs either by facilitative diffusion along a natural glucose concentration gradient or by an active sodiumcoupled transport system against the glucose concentration gradient. During the past decade, the molecular structure, function and location of glucose transporters (GTs) has been extensively studied, leading to a rather detailed knowledge of the mechanisms underlying sugar transport in biological tissues (for review see Bell et al., 1990; Kasanicki and Pilch 1990; Thorens et al., 1990; Bell et al., 1993; Partridge and Boado, 1993).

Collectively, the sodium-independent ‘facilitative’ glucose transporters form a small multigene family of structurally and functionally related integral transmembrane proteins. Despite their close relationship, facilitative GTs exhibit distinct kinetic properties and show a pronounced tissue-specific expression pattern. To date, seven members of the facilitative GT family have been described and their cDNAs have been cloned and sequenced. These sequences, including one non-functional pseudosequence (Glut 6) (Kayano et al., 1990), were termed Glut 1 to Glut 7, referring to the order in which they were identified.

This chapter focuses on the developmental expression of the major facilitative glucose transporters in the mammalian brain. Facilitative GTs of tissues other than the brain are not discussed further.