ABSTRACT
Endothelial monolayer hyperpermeability is regulated by a myosin light chain phosphorylation (MLCP)-dependent contractile mechanism. In this study, we tested the role of Src-dependent tyrosine phosphorylation to modulate endothelial contraction and monolayer barrier function with the use of the myosin phosphatase inhibitor calyculin A (CalA) to directly elevate MLCP with the Src family tyrosine kinase inhibitor herbimycin A (HA) in bovine pulmonary artery endothelial cells (EC). CalA stimulated an increase in MLCP, Src kinase activity, an increase in the tyrosine phosphorylation of paxillin and focal adhesion (FA) kinase (p125(FAK)), and monolayer hyperpermeability. Microscopic examination of CalA-treated EC revealed a contractile morphology characterized by peripheral contractile bands of actomyosin filaments and stress fibers linked to phosphotyrosine-containing FAs. These CalA-dependent events were HA sensitive. HA alone stimulated an improvement in monolayer barrier formation by reducing the levels of MLCP and phosphotyrosine-containing proteins and the number of large paracellular holes. These data show that Src kinase plays an important role in regulating monolayer hyperpermeability through adjustments in tyrosine phosphorylation, MLCP, and EC contraction.
Subject(s)
Capillary Permeability/physiology , Endothelium, Vascular/metabolism , src-Family Kinases/metabolism , Animals , Benzoquinones , Capillary Permeability/drug effects , Cattle , Cell Size/drug effects , Cell Size/physiology , Cells, Cultured , Cytoskeletal Proteins/metabolism , Endothelium, Vascular/cytology , Endothelium, Vascular/drug effects , Enzyme Inhibitors/pharmacology , Focal Adhesion Protein-Tyrosine Kinases , Lactams, Macrocyclic , Marine Toxins , Myosin Light Chains/metabolism , Myosin-Light-Chain Phosphatase , Oxazoles/pharmacology , Paxillin , Phosphoprotein Phosphatases/antagonists & inhibitors , Phosphoproteins/metabolism , Phosphorylation/drug effects , Protein-Tyrosine Kinases/metabolism , Quinones/pharmacology , Rifabutin/analogs & derivativesABSTRACT
OBJECTIVE: To characterize the effects of size, shape, and negative charge on the transport of macromolecules across the glomerular capillary wall by using the sieving curves (fractional clearance vs. solute molecular radii) of fluorescent polydispersed polysaccharide tracers. METHODS: Glomerular fractional clearances (FC) were measured with fluorescent neutral [isoelectric point (pI) = 7.3 +/- 0.2] and negatively charged (pI = 3.5 +/- 0.4) dextrans (DEX) in comparison with negatively charged (pI = 4.8 +/- 0.3) hydroxy ethyl starch (HES) and (pI = 4.6 +/- 0.1) bovine serum albumin (BSA) in Sprague-Dawley and Fischer 344/Brown Norway rats. FCs (n = 53) were measured by using the urinary clearance of (14)C-inulin to determine the glomerular filtration rate. The relative uptake of each fluorescent probe by endothelial and renal proximal tubule epithelial (LLC-PK(1)) cells, in vitro, was measured microscopically by using a cooled (-25 degrees C) CCD camera. RESULTS: The sieving curves for randomly coiled neutral and negatively charged DEX probes were identical. These FC values were 6-fold greater than those for HES and 200-fold above similarly sized fluorescent BSA. The polysaccharide probes did not show significant binding to serum proteins. The uptake of BSA by LLC-PK(1) cells was 20- to 100-fold greater than that for neutral or negatively charged macromolecules. CONCLUSIONS: These findings indicate that the rat glomerular filtration barrier restricts the transport of polysaccharide macromolecules as a function of their size and configuration but not negative charge.