Complex organisms use chemical signals, e.g., hormones and growth factors, to integrate and coordinate the function of specialized tissues. Information is transferred to target cells when chemical signals bind to specific surface receptors and, as a result, cell structure and function can be profoundly altered. This project is concerned with events that occur after such signals are received, intracellular events that transmit the information from the surface receptor to the cell's biochemical machinery. To study how information flows to metabolic control points, we have developed a powerful experimental system, consisting of a giant cell (amphibian oocyte), paraffin oil-based cell microinjection and microdissection procedures and single cell analyses. Recent experiments have focussed on the actions of insulin and certain heavy metal salts (vanadate and Zn++), which, at low concentrations, act as insulin mimics. We found that a peroxide of vanadate (pervanadate) rather than vanadate itself is the form of the ion that stimulates hexose uptake and protein synthesis. In addition hexose uptake, but not protein synthesis, is stimulated by microinjected, intracellular pervanadate. Pervanadate stimulates protein synthesis (but not hexose uptake) by a Mg-dependent mechanism, increasing Mg influx at the surface membrane. Since translation is particularly sensitive to intracellular Mg, increased influx appears to signal increased translation. Future plans include: 1) determining the mechanisms by which external and internal pervanadate affect the function of oocytes and somatic cells, 2) examining the role of intracellular Mg in metabolic control, and 3) determining how other heavy metal ions, which act as insulin mimics at low concentrations, disrupt cellular control mechanisms.
