BETAINE IS AN OSMOLYTE IN RAW-264.7 MOUSE MACROPHAGES

Hyperosmotic (405 mosmol/l) exposure of RAW 264.7 mouse macrophages le d to a stimulation of betaine uptake and an increase in betaine transp orter (BGT-1) mRNA levels, Conversely, hypoosmotic (205 mosmol/l) expo sure decreased betaine uptake and diminished BGT-1 mRNA levels. Betain e uptake was Na+-dependent and was inhibited by about 90% by GABA, whe reas inhibition by methylaminoisobutyrate and myoinositol was less tha n 15%, Addition of betaine strongly diminished BGT-1 mRNA levels in ce lls exposed to normoosmotic or hyperosmotic media, When mouse macropha ges were preloaded with betaine, lowering of the extracellular osmolar ity was followed by a rapid betaine efflux from the cells, This study identifies a constitutively expressed and osmosensitive betaine transp orter in RAW 264.7 macrophages and the use of betaine as an osmolyte i n these cells.