Biochemistry and physiology of carbohydrates in the renal collecting duct

Abstract

Using 13C‐NMR analysis of cell extracts, enzymatic determination of metabolites and cofactors as well as enzyme assays on cell homogenates aerobic and anaerobic glycolysis, sorbitol formation by aldose reductase, the pentose phosphate shunt, and gluconeogenesis could be identified as the major pathways of D‐glucose metabolism in renal inner medullary collecting ducts. In flux studies it was shown that D‐glucose enters the collecting duct cells via a sodium‐independent, cytochalasin‐ and phloretin‐inhibitable transport system located at the basal‐lateral cell side. At the same side sorbitol leaves the cells during regulatory volume decrease in a calcium‐calmodulin‐dependent fashion. From cell isolation studies it is proposed that sorbitol is taken up by adjacent (interstitial) cells, converted into fructose and then recycled to the collecting duct cells. This cycle might prevent carbohydrate wasting. Thus, IMCD cells exhibit unique aspects of carbohydrate biochemistry and physiology which enable them to function in a surrounding of low oxygen tension, low substrate supply, and extreme changes in extracellular osmolality. J. Exp. Zool. 279:436–442, 1997. © 1997 Wiley‐Liss, Inc.

Phenotypic Plasticity in Animals Exposed to Osmotic Stress – Is it Always Adaptive?

“…In 15‰ brackish water, however, the hydranths are slim and extremely elongated and carry more tentacles (Figure B). At high salinities (30‰) (Figure C), the hydranths are slim as well, but stay much shorter than in animals reared in 15‰ media . Salinity‐dependent formations of these hydranth morphotypes go along with characteristic changes in cell morphology affecting both ectodermal and endodermal cells (Figure , lower panels).…”

“…Differences in hydranth shape and cellular architecture in polyps of Cordylophora caspia (Hydrozoa) upon exposure to different salinities in the medium for a few days. Data have been compiled from several publications …”

“…At 15‰, ecto‐ as well as endodermal cells show intermediate phenotypes . Besides changes in cell size and shape, the number of cells in Cordylophora hydranths differ when animals are exposed to different salinities for days or weeks being significantly higher in animals reared in freshwater than in those exposed to a salinity of 30‰ …”