PERMEABILITY TO ALBUMIN IN ISOLATED CORONARY VENULES

This study reports measurements of albumin permeability in isolated co ronary venules. The isolated microvessel technique allows the quantifi cation of transmural exchange of macromolecules under tightly controll ed physical and chemical conditions. Transvenular exchange of albumin was studied in isolated coronary venules during alterations in filtrat ion rate caused by changes in intravascular pressure. The apparent per meability coefficient of albumin (P(a)) at an intraluminal pressure of 11 cmH2O was 3.92 +/- 0.43 x 10(-6) cm/s. Elevating intraluminal pres sure to 16 and 21 cmH2O increased P(a) to 5.13 +/- 0.57 x 10(-6) and 6 .78 +/- 0.66 x 10(-6) cm/s, respectively. Calculation of the true diff usive permeability coefficient of albumin (P(d)) at zero filtration ra te was 1.54 x 10(-6) cm/s. The product of hydraulic conductance (L(p)) and (1 - sigma), where sigma is the solute reflection coefficient, wa s 3.25 x 10(-7) cm.s-1. cmH2O-1. At a net filtration pressure of 4-5 c mH2O, diffusion accounts for >60% of total albumin transport across th e venular wall. Transmural albumin flux is very sensitive to filtratio n rate, rising 6.7% for each cmH2O elevation of net filtration pressur e. At 11 cmH2O net filtration pressure, convection accounts for nearly 70% of net albumin extravasation from the venular lumen. We suggest t hat the isolated coronary venule is a suitable preparation for the stu dy of solute exchange in the heart.