Heavy water ( 2H 2O) as solvent for incubation media in vitro: Effects on two tissues exhibiting significant water shifts: Mammalian cerebral cortex and etiolated pea seedlings

Abstract

Apical stem segments from 7-day-old etiolated pea seedings when incubated in vitro in the presence of 10 −6 M indolyl-3-acetic acid (IAA) normally exhinit significant elongation and a significantly greater (3-fold) imbibition of fluid than control stem segments. In the presence of an incubation medium made up with 2H 2O (85%, v/v) as solvent, these effects of IAA are completely absent. Swelling of slices of cat cerebral cortex normally encountered upon incubation in vitro was unaffected by incubation in media made up with 2H 2O (99%, v/v) as solvent except for: (1) slices from neonatal kittens, normally resistant to swelling in vitro, where 16% swelling was encountered; and (2) slices from adult cats when incubated in 2H 2O media containing 5 mM K +, where a 2-fold increase in swelling was encountered. In the latter case, tissue fluid spaces accessible to sucrose and to chloride did not change proportionately, suggesting an intracellular locus for the extra fluid of swelling. Contents of electrolytes in control and 2H 2O-treated slices were similar except for K +, which was significantly elevated (+ 18–24 μmoles/g) in slices incubated in 2H 2O media containing either 5 mM or 27 mM K +. The findings are discussed in terms of known effects of 2H 2O on various biological systems, including plant tissues and the mammalian nervous system.