Betaine is an osmolyte in RAW 264.7 mouse macrophages

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Abstract
Hyperosmotic (405 mosmol/l) exposure of RAW 264.7 mouse macrophages led to a stimulation of betaine uptake and an increase in betaine transporter (BGT‐1) mRNA levels. Conversely, hypoosmotic (205 mosmol/l) exposure decreased betaine uptake and diminished BGT‐1 mRNA levels. Betaine uptake was Na+‐dependent and was inhibited by about 90% by GABA, whereas inhibition by methylaminoisobutyrate and myoinositol was less than 15%. Addition of betaine strongly diminished BGT‐1 mRNA levels in cells exposed to normoosmotic or hyperosmotic media. When mouse macrophages were preloaded with betaine, lowering of the extracellular osmolarity was followed by a rapid betaine efflux from the cells. This study identifies a constitutively expressed and osmosensitive betaine transporter in RAW 264.7 macrophages and the use of betaine as an osmolyte in these cells.