Transport of tracer albumin across rat lung microvessels. Effects of cooling, N-ethylmaleimide (NEM) and filipin
Research field:Cardiovascular physiology
Authors:Rippe B, Taylor A
Address of presenting
author:		Department of Nephrology
University of Lund
S-221 85 Lund, Sweden

Department of Physiology
University of South Alabama
Mobile, 36688 Al, USA
E-mail:Bengt.Rippe@njur.lu.se
Phone:+46-46-172155
Fax:+46-46-2114356
Text of abstract Introduction
The present experiments were performed to evaluate the role of transcytosis as a bulk transfer mechanism for the passage of albumin from blood to tissue in isolated, continuously weighed rat lungs, perfused with an albumin–serum-buffer solution. Schnitzer et al, have in in situ perfused lungs demonstrated markedly inhibited transport of albumin induced by NEM or filipin.

Methods
Isolated perfused rat lungs were continuously weighed and perfused under strictly controlled hemodynamic conditions, which allowed measurements of the capillary filtration coefficient (LpS) as well as plasma to tissue clearances of 131I-albumin and 125I-albumin. Measurements could be made under strictly isogravimetric conditions to obtain an apparent "albumin PS" (Cliso) or at elevated filtration rates, to obtain an "apparent reflection coefficient" for albumin (salb). 0.13 mM NEM (n=5) and 0.22-1.8 mg/ml filipin were used as transcytosis inhibitors.

Results
Cooling to 22oC caused moderate (30%) increases in vascular resistance and reductions in LpS and also a tendency towards reduction in Cliso (from 0.230±0.19 to 0.167±1.34 ml/min/100g) with no significant changes in salb. NEM caused a marked increase in Cliso to 0.374±0.048 ml/min/100g, n=5 (p<0.05) and also a marked reduction in s, concomitant with moderate increases in LpS. Filipin (n=6) caused no significant changes in either Cliso, salb or LpS at low doses, whereas Cliso seemed to increase at high doses.

Conclusions
In conclusion, tissue cooling produced only moderate reductions in Cliso, while NEM and filipin did not reduce albumin transport at all. NEM and high doses of filipin rather caused an increase in lung microvascular permeability. The present study supports the notion of passive, pore-bound transfer of albumin across the endothelium in rat lungs.

References
Schnitzer, JE et al. 1994. Am J Physiol 268, H48-H55

Schnitzer, JE et al. 1994. J Cell Biol 127, 1217-1232

Keywords:capillary permeability, albumin, lung, capillary filtration coefficient, clearance

Created 2000-05-03