Membrane bound and cellular cationic changes associated with insulin stimulation of cultured cells

Insulin was employed as a stimulant in our continuing investigations of the molecular mechanisms involved in the coordinate control of cellular metabolism and growth. Incubation of chicken embryo fibroblasts for 16 hours in media containing 0-0.1 U insulin/ml resulted in a 17-fold increase in the rate of 3H-thymidine incorporation into DNA. Concomitantly, there were graded increases in intracellular K+ (14%) AND Mg2+ (22%) and no significant change in Ca2+. These changes in cation content occurred within 10 to 30 minutes and preceded the changes in 3H-thymidine incorporation. Insulin produced a consistent graded decrease in externally bound Mg2+ and Ca2+ and a concomitant increase in bound Na+ and K+ with no significant change in the rates of K+ and Mg2+ efflux. The results are consistent with the concept of Mg2+ as a second messenger for insulin action, as well as with the more general hypothesis that Mg2+ is the centtral agent in the coordinate control of metabolism and growth in animal cells.