Importance of charge on transvascular albumin transport in skin and skeletal muscle.

To test the hypothesis that charge affects the transvascular transport of albumin, the tracer clearance for albumin and a set of charge-modified albumins was measured in heel skin and gastrocnemius muscle from anesthetized rabbits. The charge on albumin was made less negative by modifying the carboxyl groups of aspartic and glutamic acids to alcohol groups. Four preparations of modified albumin having isoelectric points of 5.1 +/- 0.4, 5.8 +/- 0.4, 7.1 +/- 0.5, and 8.1 +/- 0.7 were studied. In skin, the clearances for the most neutral modified albumin and cationic albumin were 20 and 80% greater than that for native albumin, respectively. In skeletal muscle, the clearances for the most neutral modified albumin and cationic albumin were 50% and 1.5 times greater than that for native albumin, respectively. Calculation of the reflection coefficient for native albumin from the change in clearance with increased venous pressure resulted in estimates greater than 0.95 in both tissues. The change in clearance for the modified albumins during increased venous pressure was not different from that for native albumin. Charge appears to effect transvascular diffusion of proteins more than convective transport.