Bicarbonate dependency of betaine synthesis in cultured LLC-PK1 cells
Moeckel, G.W.; Lien, Y.H.
American Journal of Physiology 266(3 Pt 2): F512-F515
1994
ISSN/ISBN: 0002-9513 PMID: 8160802 Document Number: 430490
Betaine, one of the major renal organic osmolytes, is synthesized from choline by choline dehydrogenase (EC 1.1.99.1) and betaine-aldehyde dehydrogenase (EC 1.2.1.8) in the kidney. A recent in vitro study has shown that betaine synthesis by renal cortical homogenate is dependent on millimolar amounts of bicarbonate. The present study was aimed to investigate the bicarbonate dependency of betaine formation in cultured LLC-PK-1 cells. The data show that betaine formation increases in accordance with a rise in extracellular bicarbonate levels. The measured quantities of (14C)betaine synthesis ranged from 13.4 +- 1.5 (4.6 mM HCO-3-) to 38.0 +- 1.4 pmol cntdot mu-g protein-1 cntdot h-1 (24 mM HCO-3-). The carbonic anhydrase inhibitor acetazolamide, added to the incubation medium to block bicarbonate transport, reduced betaine synthesis from choline by 41-49%. We conclude that betaine synthesis in LLC-PK-1 cells is dependent on extracellular bicarbonate levels and is reduced by the inhibition of carbonic anhydrase. Because betaine accumulates in renal medulla during antidiuresis, our observations suggest a possible link between acid-base homeostasis and concentration mechanisms in the kidney.