Mechanisms of Magnesium Transport

Abstract

Mg, the second or third most abundant intracellular cation, is an important constituent of cells and is a necessary cofactor for many enzymes especially those involved in the transfer of phosphate groups. In this role Mg is essential for Na and Ca pump activity. Recently it has been shown to regulate the activity of the Na,K,CI (18) and K,CI (39) co-transport systems and to influence ionic traffic through Ca (34), K (37), and Na (48) channels. Mg may thus be an important link between ion transport and metabolism, and it is likely that its cytoplasmic concentration is precisely regulated. This chapter will focus on how Mg crosses the membrane and on some of the factors that influence the process. It will show how models initially formulated to de­ scribe Mg transport in squid axon and barnacle muscle have been used to explain recent observations on red cells. The earliest experiments on Mg transport suggested it was difficult to change cell Mg content. Several cell types had been incubated for long periods in media containing either high Mg concentrations or Mg chelators without significantly affecting cell Mg content. This, together with the observation that 28Mg equilibrated very slowly across some cell membranes, suggested that membranes had a particularly low Mg permeability (17, 19)