Individual capillaries of frog mesentery were perfused using a micropipet and superfused with frog Ringer containing the test solutes. Following occlusion of the capillary, the initial osmotic flows per unit area of capillary, (ΔJv/S)0, were measured using the methods of Curry et al. (J. Physiol. 261, 319-336). When the perfusion rate, Q, was high, (ΔJv/S)0 was independent of Q; at lower perfusion rates, (ΔJv/S)0 decreased as Q decreased. Permeability coefficients, P. were calculated from the fractional reduction of the osmotic flows in capillaries where both perfusion rate and surface area were measured directly. Capillary filtration coefficients (Lp) and osmotic reflection coefficients (σ) were also determined. Calculations based on measured σs showed that the effect of solute sieving on the estimates of P was small. Three experiments to measure directly the concentration of potassium ion in the fluid on both sides on the capillary wall indicate the diffusion resistance outside the capillary wall was negligible. At least two solutes were tested on each capillary. At 14-18° the mean PNaCl was 4.40 ± 0.67 (range 1.25-10.8) × 10-4 cm sec-1 (15 capillaries). The mean Psuctuse was 1.43 ± 0.36 (range 0.32-4.8) × 10-4 (13). Urea, glucose, and raffinose were test solutes in smaller samples. What factors determine the number of pathways for water and hydrophilic solutes (of approximately constant equivalent pore size) across the walls of continuous capillaries?
ASJC Scopus subject areas
- Cell Biology
- Cardiology and Cardiovascular Medicine