ABSTRACT
This chapter discusses the regulation of the methylamines proline betaine, trimethylamine oxide, and glycine betaine by osmotically stressed animal cells. In response to volume changes produced by exposure to anisosmotic conditions, most cells attempt to recover volume by regulating intracellular osmolyte concentrations. Proline betaine is also regulated in Elysia transferred to dilute medium. In whole animal experiments, exposure to hypoosmotic conditions produces swelling, which corresponds to the severity of the osmotic shift. Regardless of the magnitude of the nonlethal hypoosmotic shock, the animals at least partially recover volume. Trimethylamine oxide is an osmolyte found predominantly in urea-concentrating organisms, such as the elasmobranchs. Glycine betaine is a very common and important methylamine used in cellular osmoregulation. Glycine betaine is an important osmolyte in the mammalian kidney. Cells from the cortex, outer medulla, and inner medulla are able to synthesize glycine betaine; however, only the cortical oxidation of choline is responsive to osmotic perturbations.
