AJP - Renal Physiology, Vol 266, Issue 3 512-F515, Copyright © 1994 by American Physiological Society
Bicarbonate dependency of betaine synthesis in cultured LLC-PK1 cells
G. W. Moeckel and Y. H. Lien
Department of Medicine, University of Arizona Health Sciences Center, Tucson, Arizona 85724.
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-PK1 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 HCO3-) to 38.0 +/-
1.4 pmol.micrograms protein-1.h-1 (24 mM HCO3-). 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-PK1 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.
