Betaine plays an important role in the osmoregulation of various renal cells. In the kidney betaine synthesis seems to be highest in the cortex, whereas osmotically regulated accumulation seems to play a crucial role in the inner medulla. Therefore, the influence of betaine synthesis on the long-term osmotic regulation of betaine content was investigated in epithelial SV40 transfected cell culture, derived from the outer medullary thick ascending limb of the loop of Henle (TALH) of rabbit kidney. Under hyperosmotic conditions the betaine content of TALH was significantly increased from 218 +/- 35 mumol/g protein (300 mOsm/liter; control) to 334 +/- 27 mumol/g (600 mOsm/liter; P < 0.0005). In addition the intracellular accumulation of 14C-betaine from 14C-choline was significantly elevated from 4.3 +/- 1.0 mumol/g protein x hr) to 8.2 +/- 1.0 mumol/g protein x hr; P < 0.001) under hyperosmotic conditions. Synthesis of betaine was also influenced by the extracellular betaine content. In a betaine free medium the synthesis of betaine was increased by 7% (300 mOsm/liter; NS) or 40% (600 mOsm/liter; P < 0.0001) when compared to betaine containing medium. The alteration of betaine synthesis is presumably caused by osmotic regulation of the betaine aldehyde dehydrogenase. Activity of this enzyme was significantly higher under hyperosmotic conditions compared to isoosmotic control conditions (Vmax 4.1 +/- 0.8 U/g protein; 600 mOsm/liter) versus 1.4 +/- 0.1 U/g (300 mOsm/liter; P < 0.0001), while the affinity to betaine aldehyde remained unaltered. These results demonstrate that during long-term adaptation, betaine synthesis in TALH cells of the outer medulla of rabbit kidney can be regulated by extracellular osmolarity.
BACKGROUND: Existing survey and administrative data provide little information on why individuals with disabilities have had persistently low employment rates and why some groups of individuals fare better in the labor market than others. OBJECTIVE: Our goal is to provide new insights into the barriers and facilitators to employment among individuals with disabilities. METHODS:We designed the Survey of Disability and Employment, a 30-minute telephone survey, to collect information on health conditions, employment history and barriers, and workplace and social supports for 2,804 vocational rehabilitation (VR) applicants in 2014. RESULTS:In addition to citing health issues, VR applicants cite many barriers to employment, including difficulty finding a job, lack of skills, and accessibility. Health presents as a barrier due to unpredictability of symptoms, pain, and lack of physical energy and adequate time. Despite these barriers, the majority of VR applicants state it is extremely important that they work and most have high self-perceptions of executive functioning. CONCLUSION: A richer understanding of the resources and needs of individuals with disabilities can help counselors and policymakers better tailor services to support their employment goals.
Organic osmolytes, such as sorbitol, inositol, glycerophosphorylcholine, and betaine, play an important role in the osmoregulation of inner medullary cells of the kidney. The cells of the outer medulla are also exposed to elevated NaCl and urea concentrations during antidiuresis. Therefore, we investigated the mechanisms involved in the regulation of outer medullary organic osmolytes, especially cell sorbitol content of immortalized epithelial cells of the thick ascending limb of Henle's loop (TALH). In the cultured cell model, a 600 mosmol/l medium (osmolarity adjusted by addition of 150 mM NaCl or 300 mM sucrose) increased the intracellular sorbitol content significantly compared with a 300 mosmol/l medium. The accumulation of sorbitol appeared to be due to an increase of aldose reductase activity, which catalyzed sorbitol synthesis. Sorbitol degradation by sorbitol dehydrogenase was not detectable under our experimental conditions. After a sudden decrease of the extracellular osmolarity, the sorbitol permeability of the cellular membrane increased sevenfold within 10 min compared with isosmolar conditions. These results indicate that sorbitol, like inositol, plays an important role in the osmoregulation of TALH cells. Although the short-term regulation involves rapid changes in sorbitol membrane permeability, the longterm adaptation to low osmolarities is regulated by intracellular sorbitol synthesis.
Background: The organic osmolyte sorbitol plays an important role in the osmoregulation of immortalized epithelial cells of the thick ascending limb of Henle’s loop (TALH) of rabbit. The intracellular sorbitol content seems to depend strongly on the extracellular osmolarity. To investigate the nature of the osmotic regulation we characterized the aldose reductase. Methods: We determined aldose reductase activity enzymatically and the content of organic osmolytes by HPLC. Results: The aldose reductase activity correlates with the extracellular tonicity. Elevating the osmolarity of the medium from 300 to 600 mosm/l by addition of NaCl or sucrose resulted in a significant increase of maximal velocity (Vmax) of the adapted cells from 8 ± 1 µmol/g × min (300 mosm/l) to 322 ± 28 µmol/g × min (600 mosm/l, NaCl) or 54 ± 9 µmol/g × min (600 mosm/l, sucrose), respectively, while affinity (Km) remained unchanged. But we found no rise of aldose reductase activity when extracellular urea concentration was elevated. Similar alterations in Vmax were observed when the activity of the highly enriched enzyme was determined with glucose as substrate. Elevation of the extracellular osmolarity by NaCl and sucrose strongly induced the expression of aldose reductase protein with an apparent molecular weight of 39 kD. The affinity of glucose is characteristically low with a Km above 300 mmol/l. Aldose reductase utilizes both NADPH and with lower affinity NADH as coenzymes. In vitro sulfate ions (0.4 mol/l) results in a two-fold activation of the aldose reductase activity whereas sodium (200–400 mmol/l) decreased the activity significantly (22–33%). Potassium and chloride up to 400 mmol/l did not alter the aldose reductase activity in vitro. Conclusions: These results indicate that the aldose reductase of TALH cells of the outer medulla is osmotically regulated and has many similarities with aldose reductase in renal inner medulla. Therefore, intracellular sorbitol synthesis seems to be of similar importance in the osmoregulation of TALH cells as in the inner medulla.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.