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R W Grunewald

Publications and source records attributed to R W Grunewald.

43 records · Page 3Linked to original sources
PubMed1988

[Transport mechanisms and metabolic processes in isolated cells of the collecting tubule of the kidney papilla].

Taking into account recent results obtained with isolated papillary collecting duct cells the metabolic pathways and membrane transport systems of collecting duct cells are reviewed. The plasma membranes contain a luminal proton AT-Pase and a contraluminal Cl-/HCO3- exchanger which are involved in proton secretion; a luminal sodium channel and a contraluminal Na+/K+-AT-Pase for sodium reabsorption; a K+ channel for potassium secretion, and a Na+/K+/Cl- cotransport system for chloride transport and/or volume regulation. The plasma membranes also possess transport systems for organic substrates and organic osmolytes. D-glucose, the main substrate of the papillary collecting duct is taken up into the cell by a sodium-independent D-glucose transport system with a Km of 1.2 mM. The plasma membrane also contains mechanisms which mediate sorbitol release into the medium. This mechanism is stimulated when cells are exposed to media with a low osmolality and inhibited when cells are exposed to media with a high osmolality. D-glucose is used as metabolic substrate in anaerobic and aerobic glycolysis and as precursor for sorbitol synthesis via the aldose reductase, which is highly enriched in papillary collecting duct cells. The cells also show gluconeogenic activity as evidenced by incorporation of labeled carbon from L-alanine into glycerol, sorbitol, and myo-inositol. Accordingly, the cells show fructose-1,6-biphosphatase activity. Sorbitol synthesis in contrast to sorbitol permeability is not affected by osmolarity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Sugar transport in isolated rat kidney papillary collecting duct cells.

D-Glucose is an important substrate of energy metabolism and osmolyte synthesis in the renal papillary collecting duct. In order to characterize the cellular entry of D-glucose in this tubular segment, collecting duct cells were isolated from rat kidney papilla and the rate of D-glucose uptake was measured indirectly by monitoring the D-glucose-dependent O2 uptake in the presence of the uncoupler CCCP. D-Glucose uptake was found to be sodium-independent and not sensitive to phlorizin even at a concentration of 10(-3) M. Uptake was, however, completely inhibited by 10(-5) M cytochalasin B and 10(-4) M phloretin. The apparent Ki for cytochalasin B was 1.5 x 10(-6) M and for phloretin 2.0 x 10(-5) M. Studies on the substrate specificity revealed that at 1 mM D-mannose is taken up and metabolized to the same extent as D-glucose. A 50-fold higher concentration of 2-deoxy-D-glucose and 2-amino-2-deoxy-D-glucose inhibited D-glucose uptake completely whereas alpha-methyl-D-glucoside, D-allose, and D-galactose were without effect. Under conditions where D-glucose utilization was maximally stimulated an apparent Km of 1.2 mM and a Vmax of 1 mmol D-glucose/g protein.hour was found for D-glucose uptake. These results indicate that the D-glucose uptake into papillary collecting duct cells is probably mediated by a transport system similar to the one found in basal-lateral membranes of polarized renal, intestinal, and liver cells as well as in nonpolarized fat cells and erythrocytes.

Animals↗
PubMedDate not supplied

Volume regulation of thick ascending limb of Henle cells: significance of organic osmolytes.

The thick ascending loop of Henle (TALH) is exposed to high osmotic stress, which is particularly due to high sodium and chloride reabsorption and very low water permeability of the luminal membrane. Therefore, the volume regulation of TALH cells, derived from the TALH loop of rabbit kidneys, was analyzed. The volume was determined by impedance measurements. TALH cells, which were adapted to different osmolarities (300 and 600 mosm/l), showed no significant differences in their cell volume. Therefore, a complete volume regulation could be supposed. An increase in extracellular osmolarity from 300 to 600 mosm/l (osmolarity adjusted by addition of 150 mM NaCl) immediately led to a reduction in the cell volume by 37 +/- 6% (n = 6). A regulatory volume increase (RVI) was not observed within 10 min but after 24 h. Conversely, a sudden cell swelling by 44 +/- 5% (n = 4) was detected within 20 s following an extracellular hypoosmotic challenge (from 600 to 300 mosm/l). The subsequent volume regulatory decrease (RVD) required a period of 7 days. Specific inhibitors of important ion transporters had no effect on volume regulation. Thus, changes in the ion conductivity do not seem to influence the processes of RVI and RVD. Conversely, the intracellular content of the organic osmolytes, sorbitol, inositol, betaine, and glycerophosphorylcholine, changed in the course of RVI and RVD. These results provide evidence that TALH cells are capable of maintaining their volume despite large extracellular osmotic changes. RVI and RVD are mainly regulated by changes in the intracellular content of organic osmolytes within 1 and 7 days.

Animals↗