AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 2 426-R431, Copyright © 1994 by American Physiological Society
Taurine, betaine, and inositol share a volume-sensitive transporter in skate erythrocyte cell membrane
L. Goldstein and E. M. Davis
Section of Physiology, Brown University, Providence, Rhode Island 02912.
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.
