Effects of human alpha-thrombin and 8bromo-cAMP on large and microvessel endothelial monolayer equivalent "pore" radii.

Previous studies have reported that endothelial cells isolated from large vessels compared with microvessels from the same or distinct organs showed considerable phenotypic and biochemical heterogeneity. In the present study we extend these findings by comparison of the effects of 8-bromo-cyclic adenosine monophosphate (8Br-cAMP), human alpha-thrombin, 8Br-cAMP followed 5 min later by thrombin or no treatment (control) on the equivalent "pore" radii (rp) of endothelial monolayers isolated from the main bovine pulmonary artery (BPAEC) compared with lung microvessels (BLMV). BLMV, isolated from a 1-cm peripheral segment of the lung, were significantly larger than those obtained from large vessels (1602 +/- 142 microns2 vs 398 +/- microns2, respectively). In addition, BLMV monolayers formed a heteroporous barrier with less size-selectivity compared with BPAEC monolayers. 8Br-cAMP caused monolayers of both cell types to close their large "pores" which completely restricted the passage of solute molecular radii > 35-60 A across these barriers, consistent with a rp of approximately 75-100 A. This effect was due to a reduction in the area available for solute exchange (Ap) and/or an increase in the path length of the transport pathway (delta X). Human alpha-thrombin produced an increase in the Ap/delta X consistent with the formation of large open areas between adjacent cells that exposed the approximately 2000 A pore radius of the filter support. Since this effect was more marked in microvessel compared with large vessel monolayers, microvessel endothelial cells appear to be more sensitive to the effects of thrombin.(ABSTRACT TRUNCATED AT 250 WORDS)