Electron microprobe analysis of proximal tubule cellular Na, Cl and K element concentrations during acute mannitol-saline volume expansion in rats: evidence for inhibition of the Na pump

Abstract

It has previously been shown that during mannitol-saline volume expansion (VE) Na transport was inhibited 50% by harvested proximal tubular fluid without a change in paracellular shunt pathway permeability to Na. To determine whether this inhibition was due to changes in cellular entry step or an effect on the pump itself, intracellular element concentrations were measured by electron microprobe X-ray ranalysis in proximal tubular cells of control (non-expanded, NE) and VE rats. Nai, Cli and phosphorusi were increased (mean +/- S.E.) from 19.3 +/- 0.8 to 23.4 +/- 0.6, 15.8 +/- 0.4 to 21.3 +/- 0.4 and 124.3 +/- 2.6 to 138.0 +/- 1.8 mmol . kg-1 wet weight (P less than 0.001) respectively while Ki remained unchanged: 122.9 +/- 2.2 and 124.2 +/- 1.3 mmol . kg-1 wet weight. The increases in Nai and Cli were in excess of cell shrinkage produced by the hyperosmolal peritubular environment while the unchanged Ki in the face of cell shrinkage indicates and actual loss. It is concluded that mannitol-saline VE inhibits the Na pump producing a rise in Nai and a fall in Ki.

Electrogenic sodium/bicarbonate cotransport in rabbit renal cortical basolateral membrane vesicles.

“…5). Recent studies in the rat proximal tubule cell have revealed that the intracellular sodium activity measured with sodium-selective microelectrodes (27) is 13 mM, and the intracellular sodium concentration determined by microprobe analysis is 19 mmol/ kg wet wt (28). If Km for sodium is similar on both sides of the basolateral membrane, then our finding that Km for sodium is 10.3 mM suggests that the intracellular concentration of sodium may have an important role in regulating bicarbonate exit from the proximal tubular cell and thus in regulating intracellular pH (9,10).…”

Role of three-dimensional architecture in the urine concentrating mechanism of the rat renal inner medulla

“…The ascending thin limbs (ATLs) found in this region, while essentially impermeable to water (8,16,21,79), have no significant active transepithelial transport of NaCl or of any other solute (21,22,47,48). Most renal researchers believe that the generation of the inner medullary gradient involves countercurrent multiplication by the thin limbs of Henle's loops with washout of the gradient limited by countercurrent exchange in the vasa recta; however, no specific mechanism for the generation of the gradient has gained general acceptance.…”

Proximal tubular cell electrolytes during volume expansion in the rat.

“…One other possibility which must be considered as the cause for changes in the intracellular electrolyte concentrations observed here and previously is that a reduction in proximal tubular cell size was responsible for these changes. Volume expansion, in the presence of normal renal perfusion pressure, causes a reduction in cell size independent of oncotic pressure (Bentzel, 1972;Gyory et al 1985;Maunsbach, Giebisch & Stanton, 1987;present data). However, the general increase in dry weight, reflecting reduced cell volume, is most likely to be related to cell compression due to increased interstitial hydrostatic pressure (Granger, Haas, Pawlowska & Knox, 1988) and luminal pressure (Bentzel, 1972) even in decapsulated kidneys (Khraibi & Knox, 1989).…”

“…In order to investigate the role of intrinsic mechanisms within the kidney, specifically peritubular oncotic pressure and renal perfusion pressure, in mediating the natriuresis of volume expansion, the following experiments were performed. Intracellular electrolyte concentrations were determined in rats volume-expanded with albuminsaline, which maintains normal peritubular oncotic pressure and therefore normal cell size, in contrast to previous experiments using mannitol, which increases peritubular oncotic pressure (Gyory et al 1985).…”

“…shown that intracellular Na+ ([Na+]i) and intracellular CF- ([Cl]i) are increased, consistent with inhibition of the Na+ pump (Gyory, Beck, Rick & Thurau, 1985). In order to investigate the role of intrinsic mechanisms within the kidney, specifically peritubular oncotic pressure and renal perfusion pressure, in mediating the natriuresis of volume expansion, the following experiments were performed.…”