title: Determination of the magnitude of the water-exclusive pathway in cat skeletal muscle microvasculature.
abstract: OBJECTIVE
  To measure the magnitude of the water-exclusive pathway in cat skeletal muscle.
  
  
  METHODS
  The osmotic reflection coefficient (sigma d) was measured for sucrose, raffinose and cyancobalamine using osmotic transient techniques in the isolated, perfused cat hindlimb preparation at sufficiently high perfusate flows (60-80 ml/min-1 100 g-1) so that solute diffusion was not a factor. Microvascular filtration coefficient values required for the sigma d determination were measured using the capillary filtration coefficient (CFC) technique at these high flows. With these sigma d data and macromolecular reflection coefficient data from a previous study, discrete pore-modeling techniques were used to estimate the magnitude of the water movement through the water-exclusive pathway.
  
  
  RESULTS
  CFC values increased significantly at very high flows ( > 80 ml/ min-1 100 g-1), but these values were unchanged from control at the lower flows used to measure sigma d. The sigma d values for sucrose and raffinose were 0.41 +/- 0.03 SE and 0.42 +/- 0.03 SE, respectively, in 12 limbs. In the same limbs, the sigma d for cyancobalamine was 0.52 +/- 0.03 SE, which was significantly (p < 0.05) larger, consistent with a larger Stokes-Einstein radius for this molecule. A 3-pathway model (small and large pores and a water-exclusive pathway) was fit to the data. The result was that 41 +/- 4% (95% confidence interval) of total water flow makes use of the water-exclusive pathway in this preparation.
  
  
  CONCLUSIONS
  The very high fraction of water flow through the water-exclusive pathway in cat skeletal muscle suggests that this pathway is of major importance in microvascular water movement under normal conditions. Failure to take this finding into account can lead to inaccuracies in the estimation of parameters for pathways which carry solute.
authors.affiliation: Department of Physiology, University of South Carolina, School of Medicine, Columbia 29208, USA.
authors.forename: M B
authors.initials: MB
authors.lastname: Wolf
mesh_terms: D000818:Animals; D002199:Capillary Permeability / Q000502:physiology*; D002415:Cats; D066298:In Vitro Techniques; D018482:Muscle, Skeletal / Q000098:blood supply*; D009994:Osmolar Concentration; D011887:Raffinose / Q000493:pharmacokinetics*; D013395:Sucrose / Q000493:pharmacokinetics*; D014805:Vitamin B 12 / Q000493:pharmacokinetics*; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water; D013395:Sucrose; D011887:Raffinose; D014805:Vitamin B 12