Magnesium and calcium effects on uptake of hexoses and uridine by chick embryo fibroblasts.

Abstract

Cultures of chick embryo fibroblasts were incubated for varying periods in media containing different concentrations of Ca2+ and Mg2+. Mg2+ deprivation produced a gradual decrease in the Vmax of the glucose transport system for the D-glucose and 2-deoxy-D-3H-glucose and a parallel decrease in the rate of production of lactate from glucose in the medium. It greatly reduced the rates of 3H-uridine uptake and incorporation by decreasing the Vmax of the uridine transport system. Addition of Mg2+ to Mg2+-deprived cultures rapidly increased the rate of 3H-uridine uptake without requiring protein synthesis and increased the rate of 2-deoxy-D-3H-glucose uptake without requiring RNA synthesis. These effects of changes in Mg2+ concentration qualitatively reproduce the effects of such variables as cell density and serum and insulin concentrations. Ca2+ deprivation resulted in similar, though much smaller, changes in the activities of the 2 transport systems, but also greatly increased the leakiness of the cells to the nontransported hexose L-3H-glucose.