Betaine transporter cdna cloning and effect of osmolytes on its mrna induction. Ferraris, Joan D., Maurice B. Burg, Chester K. Williams, Eugenia M. Peters, and Arlyn Garc[acute]ia-P[acute]erez. Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1598
APStracts 2:0327C, 1995.
Cells generally adapt to long term hyperosmolality by accumulating compatible organic osmolytes thereby helping to normalize both volume and intracellular inorganic io concentration. When organic osmolytes are accumulated, as in renal inner medullary cells, it is the sum of their concentrations that is theoretically important. In effect, when one organic osmolyte rises, the others generally fall to maintain their sum approximately constant. The present study addresses the mechanism controlling betaine accumulation. Hypertonicity induces accumulation of betaine, sorbitol, inositol, and other organic osmolytes in PAP-HT25 cells, a line derived from rabbit renal papilla. Hypertonicity increases the betaine transporter expression in these cells. To obtain a specific probe for betaine transporter mRNA, we cloned from PAP-HT25 cells a cDNA that encodes the full protein. We then examined the effect of betaine, sorbitol, and inositol on betaine transporter mRNA abundance. Increased accumulation of any of these three organic osmolytes reduces betaine transporter mRNA. We previously observed similar results for aldose reductase, the enzyme responsible for osmotically regulated sorbitol accumulation. We conclude that the accumulation of organic osmolytes regulates betaine transporter gene expression. Since the aldose reductase gene is controlled in a similar fashion, we surmise that the two genes share a common signal for induction. 

Received 25 May 1995; accepted in final form 21 August 1995.
APS Manuscript Number C304-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.