Sodium and glucose transport across renal brush border membranes of Milan hypertensive rats

Sodium transport across luminal membranes of proximal tubules isolated from the kidney cortex of young, prehypertensive rats of the Milan hypertensive strain (MHS) and their corresponding normotensive controls, the Milan normotensive strain (MNS), was measured. A higher sodium uptake was observed in vesicles from MHS, although membrane preparations from both strains behaved similarly as far as enzyme profile and sodium-dependent glucose transport were concerned. In the presence of an inwardly directed sodium gradient, sodium uptake depended on the relative permeability of the counterion: in the presence of 100 mM NaCl, sodium transport in MHS was 26% higher than that in normotensive controls (p less than 0.05). Also, a significantly faster sodium uptake by membrane vesicles from MHS was observed when a pH gradient and an electrical potential difference (inside-negative) were imposed across the membrane. In this condition, sodium uptake by membrane vesicles from MHS was up to 39% higher than that in control MNS (p less than 0.01). Therefore, the difference in sodium transport observed between preparations of luminal membrane from the proximal tubule of MNS and MHS seems to be due to a higher rheogenic sodium pathway in the MHS. The present results are in keeping with previous data showing an increased sodium transport across renal tubules of the MHS and support the hypothesis that the abnormality in sodium and water handling by kidneys from MHS can be related to an alteration in sodium transport across the luminal membrane of the proximal tubule cells.