Most mammalian cells in culture require serum or associated components (growth factors) for sustained proliferation. In the absence of these factors, cells become guiescent. Re-addition of serum or growth factors induces a series of events which culminate in DNA replication and cell division. Many early events in this response sequence involve intracellular ion levels: there are increased transmembrane fluxs of Na+ and H+ as well as increased levels of Ca++. The aims of the proposed investigation are to: 1) determine the effect of serum and growth factors on both the short- and long-term intracellular levels of these ions; 2) to examine the mechanisms behind ion changes; and 3) to explore the effects of these changes on later events in the proliferative response, notably glycolysis. Intracellular ion activities will be monitored using both Nuclear Magnetic Resonance (NMR) and fluorescence spectroscopies of perfused cells. While fluorescence studies are more sensitive, NMR allows long time course monitoring. Glycolysis will be monitored by 13C NMR and will be analyzed by a modified crossover theorem. The unique aspects of this proposal are the long time courses involved, as well as the investigation of glycolysis.