AJP - Heart and Circulatory Physiology, Vol 256, Issue 1 282-H290, Copyright © 1989 by American Physiological Society
Measurement of osmotic reflection coefficient for small molecules in cat hindlimbs
M. B. Wolf and P. D. Watson
Department of Physiology, University of South Carolina School of Medicine, Columbia 29208.
Capillary osmotic reflection coefficients (sigma) for NaCl, urea, sucrose,
and raffinose were measured in the isolated, perfused cat hindlimb using
the osmotic transient technique. sigma were determined from the ratio of
the maximum rate of transcapillary absorption [delta Jv(max)] to the
increase in the osmotic pressure (25-35 mosmol/kg H2O) in the arterial
inflow (delta pi a) produced by adding one of the molecules to an
albumin-electrolyte perfusate containing isoproterenol (greater than 10(-7)
M). delta Jv (max) was determined from organ weight and delta pi a from
perfusate osmolalities. For each molecule, the delta Jv(max)/delta pi a
ratio increased monotonically with perfusate flow rates (Q) to Q greater
than 100 ml.min-1.100 g-1. This ratio was independent of the size of the
delta pi a. Apparent sigma values were calculated by dividing these ratios
by the capillary hydraulic capacity determined in other studies. At low Q,
apparent sigma was comparable to the approximately 0.1 values found by
others in skeletal muscle. At the highest Q, apparent sigma for these
molecules were at least 0.5. These data are consistent with at least 50% of
transcapillary water flow moving through a water-exclusive pathway.
