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Division of 1Nephrology, 2Children's Hospital, Hannover Medical School, D-30623 Hannover; 4Children's Hospital, Bonn University, D-53113 Bonn, Germany; and Departments of 3Physiology and 5Nephrology, Göteborg University, SE-405 30 Göteborg, Sweden
Submitted 20 July 2001 ; accepted in final form 14 June 2003
In a previous paper, we found that low ionic strength (I) reversibly
reduced the glomerular charge density, suggesting increased volume of the
charge-selective barrier. Because glutaraldehyde makes most structures rigid,
we considered the isolated, perfusion-fixed rat kidney to be an ideal model
for further analysis. The fixed kidneys were perfused with albumin solutions
containing FITC-Ficoll at two different Is (I = 151 and 34 mM). At normal I,
the fractional clearance (
) for albumin was 0.0049 (SE 0.0017,
+0.0027, n = 6), whereas
for neutral
Ficoll35.5Å of similar size was significantly higher 0.104
(SE 0.010, n = 5, P < 0.001). At low I,
for
albumin was 0.0030 (SE 0.0011, +0.0018, n = 6, not significant
from
albumin at normal I) and
for
Ficoll35.5Å was identical to that at normal I, 0.104 (SE
0.015, n = 6, P < 0.01 compared with
albumin at low I). According to a heterogeneous charged
fiber model, low I reduced the fiber density from 0.056 to 0.0315, suggesting
a 78% gel volume expansion. We conclude that 1) there is a
significant glomerular charge barrier. 2) Solutions with low I
increase the volume of the charge barrier even in kidneys fixed with
glutaraldehyde. Our findings suggest that polysaccharide-rich structures, such
as the endothelial cell coat, are key components in the glomerular
barrier.
glomerular permeability; charge selectivity
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