Luminal hypotonicity: a driving force for fluid absorption from the proximal tubule
Green, R.; Giebisch, G.
American Journal of Physiology 246(2 Pt 2): F167-F174
1984
ISSN/ISBN: 0002-9513 PMID: 6696118 Document Number: 229389
The ability of rat proximal tubules to generate a hypotonic luminal fluid was investigated. Simultaneous perfusion of tubules and peritubular capillaries was performed with simple solutions. When tubules were perfused at 10 nl .cntdot. min-1 and NaCl was the perfusate for tubules and capillaries, solute and fluid (0.41 nl .cntdot. min-1 .cntdot. mm-1) were transported and the luminal fluid became hypotonic (.DELTA.osmol = -1.7 mosmol .cntdot. kg-1). When the same solutions were used but the tubule was perfused at 45 nl .cntdot. min-1, more fluid (0.89 nl .cntdot. min-1 .cntdot. mm-1) was reabsorbed and the fluid became more hypotonic (.DELTA.osmol = -3.9 mosmol .cntdot. kg-1). Bicarbonate in the peritubular capillaries increased the fluid reabsorption (1.21 nl .cntdot. min-1 .cntdot. mm-1) but did not generate cryoscopically hypotonic fluid. Cyanide abolished all net movement of fluid and solute. Evidently, the proximal tubule can generate a hypotonic fluid. The hydraulic conductivity for proximal tubular epithelium is 3200-3400 .mu.m .cntdot. s-1 and the reflection coefficient for NaHCO3 is slightly higher than for NaCl.