Extracellular potassium can simulate the role of serum as an activator of uridine uptake by quiescent hamster cells in culture

Multiple controls on the intracellular trapping of uridine

Uridine uptake by mouse or hamster cells grown in conditions which support good growth is very sensitive to inhibition by cyanide and azide, at concentrations which only slightly reduce overall cellular ATP levels. Iodoacetate, when present alone, reduces uridine uptake only insofar as it reduces cellular ATP levels. At concentrations which by themselves do not affect uridine uptake, iodoacetate greatly reduces the sensitivity of uridine uptake to cyanide or azide. The effect of cyanide is on intracellular trapping of uridine and not on its transport into the cell. The specific effect of cyanide is confined to uridine and not found for the uptake of adenine, thymidine or 2-deoxyglucose. The effect is of rapid onset (within 2 min) and is rapidly reversible (also within 2 min). Phosphorylation of uridine in homogenised cells or in Triton X-100-permeabilised cells is unaffected by cyanide. The data are interpreted in terms of a model in which intracellular trapping of uridine is subject to multiple controls, including one regulated by some factor requiring intact functioning of the mitochondrion. These multiple control systems interact synergistically to affect trapping of uridine by the intact cell.

Enhancing effect of lithium and potassium ions on lectin-induced lymphocyte proliferation in aging and Down's syndrome subjects

The effect of different concentrations of LiCl or KCl (0.6-20 meq/liter) on PHA-stimulated lymphocytes from young, old, and Down's syndrome subjects was studied. LiCl showed a dramatic enhancing effect on [3H]thymidine incorporation induced by a suboptimal dose of PHA in old subjects and Down's syndrome patients. An increase of [3H]thymidine incorporation in human lymphocytes stimulated by a suboptimal dose of PHA was also observed with KCl. This effect was higher in old subjects than that observed in young and Down's subjects. LiCl and KCl can modulate and partially restore the derangement in early events of mitogen stimulation which seems to be present in lymphocytes from both old and Down's syndrome subjects.