Evaluation of Mg2+ as an intracellular regulator of uridine uptake.
The rate of uptake of the nucleoside uridine increases within minutes after adding a growth stimulus to quiescent 3T3 cells. We have previously shown this uptake rate to be highly sensitive to changes in the intracellular concentration of Mg2+. In the present paper, the alteration of uptake by Mg2+ is shown to occur at the phosphorylation step - the same point at which serum acts to modulate uridine uptake. The serum stimulation of uridine uptake can be mimicked by Mg2+ alone or blocked by partially depleting cells of their Mg2+. Work with cell-free extracts shows that the uridine kinase enzyme responds to Mg2+ in a manner similar to that exhibited by whole cells whose concentrations of Mg2+ have been raised. In addition, the enzyme's inhibition by ATP is relieved by raising the Mg2+ concentration. Thymidine uptake, a reaction which does not respond quickly to mitogenic stimulation, is unaffected by alterations in Mg2+ concentration. These results are discussed in terms of a possible role for Mg2+ as an intracellular regulator of uridine uptake and other reactions of the coordinate response of cells to external effectors.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active; D002455:Cell Division; D002460:Cell Line; D006133:Growth Substances / Q000097:blood; D008274:Magnesium / Q000502:physiology*; D051379:Mice; D013936:Thymidine / Q000378:metabolism; D013937:Thymidine Kinase / Q000378:metabolism; D014529:Uridine / Q000378:metabolism*; D014541:Uridine Kinase / Q000378:metabolism
D006133:Growth Substances; D000255:Adenosine Triphosphate; D013937:Thymidine Kinase; D014541:Uridine Kinase; D008274:Magnesium; D013936:Thymidine; D014529:Uridine