ISSN:
1432-2013
Keywords:
Microperfusion
;
Rat Proximal Tubule
;
H2O and Na Reabsorption
;
Sodium Fluxes
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary Microperfusion experiments were performed on oil-blocked tubules in non diuretic Rats, using either isotonic NaCl, or “equilibrated” solutions; perfusion rates ranged from 20 to 40 nl/min. Several recollections were made from each perfused tubule after changing either the perfusion rate or the collection site. Net fluxes of water and sodium were calculated from changes in3H-Inulin and Na+ concentrations. Unidirectional sodium efflux was calculated from22Na specific activity change. Appropriate equations were derived to account, when necessary, for the change in flow rate along the perfused tubule. Significantly different results were obtained according to the way in which calculations were made: when changes in perfusate composition taking place between the perfusion and recollection sites were used (first method), Na efflux values (expressed as nEq. per min per mm tubular length) were found to decrease as a function of the perfused distance; on the other hand, when changes in fluid composition taking place between two different recollection sites along the perfused tubule were used (second method), efflux values were found lower and constant with respect to the distance between the two collection sites. For the isotonic NaCl perfusate, larger Na and water absorption rates were found by the second than by the first method. It is concluded that the second method leads to more reliable results (although less accurate), and that the discrepancies observe reveal increased Na permeability and inhibition of Na transport along the first part of the perfused segment, due to the tubular wall impalement. For the isotonic NaCl perfusate and by using the second method of calculation, the following mean results were obtained; water absorption rate $$(\Phi _n^{{\text{H}}_{\text{2}} {\text{O}}} ):$$ 3.35 nl/min × mm; net Na efflux $$(\Phi _n^{{\text{Na}}} ):$$ 10.9 × 10-5µEq/mm2 × sec; unidirectional Na efflux $$\Phi _{lp}^{{\text{Na}}} ):$$ 34 × 10-5µEq/mm2 × sec;. None of these fluxes varied as a function of the perfusion rate. The corresponding passive over active sodium flux ratio is low $$(\Phi _{pl}^{{\text{Na}}} {\text{/}}\Phi _n^{{\text{Na}}} = 2.1)$$ . These results are discussed in relation to those of the literature.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00588454
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