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Biomedical subjects

R Kinne

Publications and source records attributed to R Kinne.

147 records · Page 9Linked to original sources
PubMedDate not supplied

The effect of parathyroid hormone (PTH) and dietary phosphate on the sodium-dependent phosphate transport system located in the rat renal brush border membrane.

The effect of two parameters regulating renal phosphate excretion, namely parathyroid hormone application and dietary phosphate intake, on the transport properties of isolated rat renal brush border membrane vesicles was investigated. In the first set of experiments brush border membrane vesicles from young normal rats injected i.m. with 30 USP parathyroid hormone or i.v. with 1 mg dibutyryl cAMP were compared. PTH and dbcAMP injection decreased specifically the Vmax of the sodium-dependent phosphate transport system by appr. 30%. In a second set of experiments rats were kept on phosphate-rich and phosphate-poor diet and after 6-8 weeks the brush border membranes were isolated. The membranes obtained from phosphate-depleted animals showed a markedly (approximately 100%) higher initial sodium-dependent phosphate uptake than membranes isolated from animals kept on phosphate-rich diet. Again only the sodium-dependent phosphate uptake was affected, sodium-independent phosphate permeability, sodium-dependent D-glucose transport, mannitol permeability and sodium permeability remained unchanged.

Animals↗
PubMedDate not supplied

What are the driving forces for the proximal tubular H+ and Ca++ transport? The electrochemical gradient for Na+ and/or ATP.

The H+ ion secretion in the proximal tubule as revealed by the reabsorption of the glycodiazine buffer vanishes when the ambient solutions are sodium-free. The same holds for other Na+-dependent transport processes such as Ca++, phosphate, glucose and amino acid reabsorption. If Na+ transport is blocked by ouabain the latter transport processes are abolished, the secretion of H+ ions, however, remains unchanged suggesting H+ to be not exclusively driven by active Na+ transport. These observations agree with electrical measurements which show an electrogenic component of H+ secretion to exist in rat proximal tubule. In experiments with isolated membrane vesicles an electroneutral Na+/H+-exchange mechanism could be demonstrated in the brush border membrane and an ATP-driven Ca++ pumpt as well as Na+-Ca++ countertransport in the baso-lateral cell membrane. These data suggest that both, the Na+ gradient and ATP, are used to drive H+ ion secretion across the luminal brush border and Ca++ reabsorption across the baso-lateral cell side. The biochemical nature of the various systems and their relative importance for the transepithelial ion movement remain to be elucidated.

Adenosine Triphosphate↗