LITHIUM-CHLORIDE DOES NOT INHIBIT THE PROLIFERATION OF L6 MYOBLASTS BY DECREASING INTRACELLULAR FREE INOSITOL

We conducted a series of experiments to determine whether lithium chlo ride (LiCl) inhibited the proliferation of L6 myoblasts by reducing th e availability of intracellular free inositol. After the myoblasts wer e plated in DMEM + 10% fetal bovine serum (FBS) for 24 h, medium was r eplaced with DMEM + 10% FBS containing 0 (control), 5, 10, or 20 mM Li Cl. Cell number, protein content, and [H-3]thymidine incorporation int o DNA were determined at 24-h intervals. Control cells exhibited a 3.8 -fold increase in cell number by 96 h in culture. Although 5 mM LiCl d id not affect the rate or extent of proliferation, 10 and 20 mM LiCl c aused 36 and 86% decreases, respectively (P <.05), in cell number by 9 6 h in culture. The effects of LiCl could not be overcome by the addit ion of free inositol (up to 20 mM) to the medium. Lithium chloride cau sed 4.6- and 7.3-fold increases (P <.05) in lactate dehydrogenase acti vity in culture media after 96 h of exposure to 10 and 20 mM LiCl, res pectively, indicating loss of viability after chronic treatment. Howev er, the acute effects of LiCl after 24 h of treatment were reversible, as indicated by a rapid resumption of proliferation following removal of LiCl. Concentrations of 5, 10, and 20 mM LiCl caused 4.7-, 8.2-, a nd 9.1-fold increases (P <.05), respectively, in the accumulation of [ H-3]inositol within the inositol monophosphate pool. Treatment of cell s with 10 and 20 mM LiCl also increased (P <.05) label recovered as in ositol bisphosphate. Rather than depress phosphoinositide synthesis, t he addition of 10 and 20 mM LiCl dose-dependently increased (P <.05) t he incorporation of [H-3]inositol into phosphatidylinositol and phosph atidylinositol-4-phosphate. These results indicate that LiCl does not decrease proliferation of L6 myoblasts via a depletion in the intracel lular free inositol pool. Instead, LiCl may block the hydrolysis of ph osphatidyl inositides.