OSMOREGULATION OF NEUTRAL AMINO-ACID-TRANSPORT

Neutral amino acids are important organic osmolytes found In most osmo tically stressed cells. During prolonged hypertonic stress, accumulati on of neutral amino acids contributes to the cell volume recovery and may protect cellular proteins against salt denaturation. Hypertonicity activates system A transport, a major neutral amino acid transporter in mammalian cells, by a microtubule-dependent mechanism. Similar to t he regulation of amino acid efflux induced by hypotonic-swelling, infl ux via system A may be under the control of Intracellular ionic streng th. An osmotically sensitive repressor may negatively regulate the gen e expression of a regulatory protein which activates the preexisting s ystem A transporter protein. Hypertonically activated protein kinases may be Involved in this osmoregulation of amino acid transport.