Integrins can mediate the attachment of cells to collagen type I. In the present study we have investigated the possible differences in collagen type I recognition sites for the alpha 1 beta 1 and alpha 2 beta 1 integrins. Different cyanogen bromide (CB) fragments of the alpha 1 (I) collagen chain were used in cell attachment experiments with three rat cell types, defined with regard to expression of collagen binding integrins. Primary rat hepatocytes expressed alpha 1 beta 1, primary rat cardiac fibroblasts alpha 1 beta 1 and alpha 2 beta 1, and Rat‐1 cells only alpha 2 beta 1. All three cell types expressed alpha 3 beta 1 but this integrin did not bind to collagen‐‐Sepharose or to immobilized collagen type I in a radioreceptor assay. Hepatocytes and cardiac fibroblasts attached to substrata coated with alpha 1(I)CB3 and alpha 1(I)CB8; Rat‐1 cells attached to alpha 1(I)CB3 but only poorly to alpha 1(I)CB8‐coated substrata. Cardiac fibroblasts and Rat‐1 cells spread and formed beta 1‐integrin‐containing focal adhesions when grown on substrata coated with native collagen or alpha 1(I)CB3; focal adhesions were also detected in cardiac fibroblasts cultured on alpha 1(I)CB8. The rat alpha 1 specific monoclonal antibody 3A3 completely inhibited hepatocyte attachment to alpha 1(I)CB3 and alpha 1(I)CB8, as well as the attachment of cardiac fibroblasts to alpha 1(I)CB8, but only partially inhibited the attachment of cardiac fibroblasts to alpha 1(I)CB3. 3A3 IgG did not inhibit the attachment of Rat‐1 cells to collagen type I or to alpha 1(I)CB3.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet-derived growth factor (PDGF) isoforms lead to mitogenic, survival, and chemotactic responses in a variety of mesenchymal cell types during development and in the adult. We have studied the importance of phosphatidylinositol-3 kinase (PI3K) signaling in these responses by mutating the PI3K-binding sites in the PDGF-␤ receptor by gene targeting in embryonic stem cells. Homozygous mutant mice developed normally; however, cells derived from the mutants were less chemotactic and had largely lost their ability to contract collagen gels in response to PDGF. Injection of a mast cell degranulating agent in mice led to a decrease in interstitial f luid pressure resulting in edema formation. In contrast to wild-type mice, mutant mice were unable to normalize the pressure after treatment with PDGF. Taken together, these observations suggest a function for PDGF signaling through PI3K in interstitial f luid homeostasis by modulating the tension between cells and extracellular matrix structures.Platelet-derived growth factor (PDGF) isoforms are potent mitogens, survival factors, and chemoattractants for many mesenchymal cell types. PDGF consists of homo-or heterodimers of A-and B-polypeptide chains, which exert their biological effects by binding to two structurally related tyrosine kinase receptors, PDGF-␣ receptor and ␤ receptor (1).The PDGF signal transduction machinery has been analyzed extensively for the PDGF-␤ receptor (for reviews, see refs. 2 and 3). Upon ligand binding, PDGF receptors homo-or heterodimerize and phosphorylate each other in trans on specific tyrosine residues, initiating signaling cascades that lead to growth, actin cytoskeleton rearrangements, and chemotaxis (1). A large body of evidence indicates that the latter two effects are dependent on activation of phosphatidylinositol-3Ј kinase (PI3K) through binding to two phosphorylated tyrosines (tyrosines 739 and 750 in the mouse sequence; refs. 4 and 5). These two tyrosines are located in Tyr-Xaa-Xaa-Met motifs and thus are recognized by the Src homology 2 (SH2) domains of p85, the regulatory subunit of the PI3K. p85, in turn, associates with the catalytic subunit p110, which phosphorylates the membrane lipids phosphatidylinositol (4)-phosphate and phosphatidylinositol (4,5)-bisphosphate in the D-3 position of their inositol rings to the corresponding (3,4)-diphosphate and (3,4,5)-triphosphate derivatives (reviewed in ref. 6). The effect of PI3K on the actin cytoskeleton, resulting in formation of lamellipodia, probably is mediated by activation of the small GTP-binding protein Rac (7-9).

1. The present experiments describe a role for platelet-derived growth factor-BB and cellular adhesion receptors towards extracellular matrix molecules (/1-integrins) in control of interstitial fluid pressure (Pif). and decreased to -2-50 + 0 35 mmHg (P < 0 05) and -3-88 + 1P45 mmHg (P < 0 05) at anti-a2/11 concentrations of 0-56 and 1P12 mg ml-', respectively.4. The effect of anti-a0231 was abolished when platelet-derived growth factor-BB (PDGF-BB) (200 ng ml-') was injected together with anti-ca2/1. 5. The time-and dose-responses of PDGF-BB to counteract increased negativity of Pif were studied further using dextran anaphylaxis as an experimental model inducing increased negativity of Pif in skin. Control Pif averaged -0 33 + 0A43 mmHg and fell to -4-10 + 1P47 mmHg within 10 min after dextran (P < 0-01). Subsequent subdermal injection of PDGF-BB at 200 ng ml-' normalized Pif in 10-20 min which became -1-37 + 1-23 mmHg (P < 0'01 versus dextran, P > 0.05 versus control). PDGF-BB had little or no effect at 50 ng ml-. PDGF-AA and basic fibroblast growth factor had no effect on Pif.6. The in vivo function reported for PDGF-BB has not been described previously and provides further evidence for active participation of connective tissue cells in control of Pif by altering tension on extracellular matrix structures.During the initial stage of several acute inflammatory reactions, loose connective tissues will 'actively' enhance transcapillary fluid flux and oedema formation in skin and airways, since an increased negativity of interstitial fluid pressure (Pif) from -1 to between -5 and -10 inmHg will provide an increased driving pressure for fluid filtration