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Reconstruction of glomeruli fixed under physiological pressures show highly restrictive routes for fluid movement to the proximal convoluted tubule (PCT)
Author(s) -
Neal Christopher Robert,
Muston P Robert,
Bates David O,
Harper Steve J
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a763-b
Subject(s) - oncotic pressure , hydrostatic pressure , glomerulus , chemistry , convoluted tubule , fixation (population genetics) , urinary system , proximal tubule , perfusion , anatomy , kidney , medicine , physics , mechanics , biochemistry , albumin , gene
We recently discovered that the urinary or Bowman’s space consists of three interconnected urinary spaces forming drainage pathways for ultrafiltrate (Neal CR et al JASN 2005 16:1223). Glomerular filtrate may enter restrictive spaces under the podocyte (subpodocyte space, SPS) before passing to other urinary spaces. The interpodocyte spaces (IPS) form channels draining filtrate to the edge of the glomerulus into the peripheral urinary space (PUS) and hence the PCT. Initial reconstructions used immersion (I) or colloid free perfusion (P) fixed kidneys, so we repeated the reconstructions after fixation at physiological oncotic and hydrostatic pressures (CP). Rat kidneys were perfused with Ringer then glutaraldehyde solutions (n=6, aortic hydrostatic pressure approx. 100mmHg; oncotic pressure 25mmHg). Kidney pieces were postfixed, dehydrated, embedded and micrographs of serial ultrathin sections were used to reconstruct regions of glomeruli. The SPS, IPS and PUS were compared with published data (Neal CR 2005). Mean±SEMs compared with unpaired t‐tests unless stated. The SPS height showed CP fixed podocytes more closely opposed to the GFB (i.e. CP, mode 0.3μm; I, modes 0.5 & 0.9μm p<0.001 Fisher’s exact test), IPS narrower (CP, 0.59±0.05μm n=6; I, 0.74±0.06μm, n=29; p<0.05), and PUS narrower (P, 8.5± 3.4 μm: CP, 2.1±0.35μm P<0.01). When glomeruli are fixed under in vivo pressure conditions the three urinary spaces are minimised. Fluid movement is more restricted than described (Neal, 2005) and incompatible with a low resistance path to the PCT. Supported by The Wellcome Trust and BHF.