ACUTE VOLUME EXPANSION: RAT PROXIMAL TUBULAR Na TRANSPORT INHIBITION BY AUTOLOGOUS TUBULAR FLUID WITHOUT CHANGES IN Na PERMEABILITY

Abstract

Summar>. Sodium permeability (PUN*) ^"^ steady state transepithelial conceniraiion differences of Na (Ac*j,) were measured in stationary droplets in proximal tubules of rais in both Ihe non-expanded (NE) and subsequent mannitol-saline volume-expanded (VE) state. The lest solutions for tubular injection were either an anificial tubular soluiion (AS) in group 1 rats or harvested proximal tubular fluid (HTF) in a second group of rats (group li)-/ic^, (mmol.kg-'HjO) was significantly reduced (p<0-001) with HTF in Ihe VE state (121 ± 0 8 SEM) when compared to HTF in the NE stale (17-8 ± 1 -8) and AS in boih NE (17-4 ± 1 -0) and VE (18-2 ± 1 -0). P;.\, calculated from Ihe half-lime of disappearance of "Na from the droplets, when using paired experimenis were 8-1 ± 1-7x10'mm^sec 'and7-3 ± 1-8 with HTF in NE and subsequent VE and 8-6 ± 1-1 and 7-7 ± 0-8 with AS in NE and VE. These permeability resulls did not differ from each other significantly. In these experiments with zero net Na and water fluxes, ihe 32% reduction of Acjg, cannot be accounted for by an increased backleak of Na. since Pi;^, would have had to increase by 32%. These resulls therefore provide strong evidence for a facior present in proximal tubular fluid consequent upon VE which inhibits Na transport without altering transcpithctial P,^,, bui do nol exclude an effect of such a factor on the cellular Na entry step or ihe Na pump itself.

Chronic volume expansion in the rat: proximal tubular Na+ transport and Na+ pump inhibition.

“…Proximal tubule Na transport is reduced in the absence of any change in plasma proteins, thus excluding any effect of peritubular oncotic pressure in this model. The degree of reduction in proximal tubular Nae transport is similar to the 25-30% inhibition obtained previously with harvested proximal tubular fluid in acute sustained volume expansion (Gyory, Willis & Chan, 1985c;Gyory et al 1985b;Reddy et al 1990). With artificial tubular fluid, during AcVE, only -20% inhibition of proximal tubular Na+ transport could be demonstrated, but using harvested proximal tubular fluid as the test solution increased this to 50% inhibition.…”

“…In early renal artery snare experiments (snare placed within 15 min of induction of AcVE), both ATF and HTF produced a 20% inhibition of proximal tubular Nae transport inhibition, indicating altered epithelial function (Reddy et al 1990) and [Na]i remained normal in these kidneys (Reddy et al 1994). The differences in transport measured with these two types of fluid are not due to basic differences in their composition for the above reasons and, in addition, in the non-expanded state Nae transport is the same with both fluids (Gyory, Willis & Chan, 1985c;Gyory et al 1985b;Reddy et al 1990) and there are no major differences in electrolyte content between these fluids after reaspiration from the tubular lumina (Reddy et at. 1990).…”