Taurine, betaine, and inositol share a volume-sensitive transporter in skate erythrocyte cell membrane.

Our previous study [J. K. Haynes and L. Goldstein. Am. J. Physiol. 265 (Regulatory Integrative Comp. Physiol. 34): R173-R179, 1993] showed that skate erythrocytes have a volume-sensitive amino acid transporter that passes amino acids across the cell membrane in a size-related nonstereospecific manner. The aim of the present study was to determine whether representatives of other groups of organic osmolytes (polyols, trimethylamines) could be transported by this same system. Volume-sensitive transport was assayed by measuring Na(+)-independent uptake of osmolytes into erythrocytes. Hypotonic stress stimulated uptake of the polyol myo-inositol and the trimethylamine betaine severalfold. There was little or no competition between osmolytes for transport. However, inhibitor studies indicated that both betaine and inositol are transported by the same pathway as amino acids. Inhibitors of the anion exchanger band 3 and a variety of chloride channel inhibitors blocked the hypotonically stimulated uptake of betaine, inositol, and taurine in a quantitatively similar manner. These results show that different chemical classes of organic osmolytes share a common volume-sensitive transporter.