Cell volume restoration following an osmotic stress is the property of every cell type. The mechanism of this volume regulation depends upon the ability of the cell to control intracellular water gain and loss by regulating the intracellular levels of ions and low molecular weight organic solutes (cellular osmolytes). Cells with the greatest volume regulatory ability have the greatest ability to control the accumulation and loss of the organic solute molecules. Dr. Popper has excellent evidence that the quaternary ammonium compound, glycine betaine, is the primary cellular osmolyte in the heart cells of the marine horseshoe. Glycine betaine is also used by a number of salt resistant strains of plants and bacteria. Popper feels that the mechanisms regulating glycine betaine levels are common to all these salt stress resistant organisms and that the heart of this crab will serve as an excellent model system for elucidating these mechanisms. Planned experiments involve characterization of some of the biosynthetic and catabolic enzyme systems, studies on uptake and utilization of precursor molecules and an evaluation of the changes in the regulation of gene expression (enzyme synthesis) under various conditions of osmotic stress. The results will have both basic science and practical value in terms of our understanding of the mechanisms of cell volume regulation and salt stress resistance.
