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), parafin 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, pervanadate, Cd++ and Zn++), which, at low concentrations, act as insulin mimics. We have found that vanadate and pervanadate stimulate hexose uptake by acting at intracellular sites and protein synthesis by acting at surface sites. Several observations indicate that vanadate, pervanadate and to a smaller extent insulin signal changes in protein synthesis by affecting Mg transport at the plasma membrane. First, rates of translation are particularly sensitive to microinjected, intracellular Mg. Second, stimulation of protein synthesis by vanadate, pervanadate and insulin depends on extracellular Mg, but not Ca; stimulation is reduced when Mg is reduced and exagerrated when Mg is raised. Third, exposing oocytes to vanadate, pervanadate or insulin causes a rapid, net influx of Mg. Future plans include: 1) characterizing further the detailed mechanisms by which insulin mimics affect the function of oocytes and somatic cells, 2) examining the role of intracellular Mg in metabolic control, and 3) determining if inappropriate cellular signalling is an important toxic effect of heavy metals that have insulin-like actions at low concentrations.
