In the integrin family, the collagen receptors form a structurally and functionally distinct subgroup. Two members of this subgroup, ␣ 1 ␤ 1 and ␣ 2 ␤ 1 integrins, are known to bind to monomeric form of type I collagen. However, in tissues type I collagen monomers are organized into large fibrils immediately after they are released from cells. Here, we studied collagen fibril recognition by integrins. By an immunoelectron microscopy method we showed that integrin ␣ 2 I domain is able to bind to classical D-banded type I collagen fibrils. However, according to the solid phase binding assay, the collagen fibril formation appeared to reduce integrin ␣ 1 I and ␣ 2 I domain avidity to collagen and to lower the number of putative ␣I domain binding sites on it. Respectively, cellular ␣ 1 ␤ 1 integrin was able to mediate cell spreading significantly better on monomeric than on fibrillar type I collagen matrix, whereas ␣ 2 ␤ 1 integrin appeared still to facilitate both cell spreading on fibrillar type I collagen matrix and also the contraction of fibrillar type I collagen gel. Additionally, ␣ 2 ␤ 1 integrin promoted the integrin-mediated formation of long cellular projections typically induced by fibrillar collagen. Thus, these findings suggest that ␣ 2 ␤ 1 integrin is a functional cellular receptor for type I collagen fibrils, whereas ␣ 1 ␤ 1 integrin may only effectively bind type I collagen monomers. Furthermore, when the effect of soluble ␣I domains on type I collagen fibril formation was tested in vitro, the observations suggest that integrin type collagen receptors might guide or even promote pericellular collagen fibrillogenesis.A fibril-forming type I collagen, a ubiquitous protein in all vertebrates, is known to provide mechanical stability for tissues and serve as a functional environment for cells (1). Depending on the physical properties of the tissue, type I collagen fibrils are arranged with different suprafibrillar architectures and diameters. Thus, narrow fibrils (ϳ20 nm) in highly ordered arrangement occur in the cornea, where optical transparency is important, whereas large diameter fibrils (ϳ500 nm) provide high tensile strength in mature tendon (2).The mechanism of type I collagen fibril formation has been under extensive research for decades. In tissues, type I collagen is synthesized as a monomeric precursor, which is secreted by exocytosis into the extracellular space. In addition to the triple helical collagenous domain, the precursor contains noncollagenous C-and N-propeptides, which are linked to the triple helical domain by short sequences called telopeptides (3). After the enzymatic removal of propeptides, the solubility of collagen monomers decreases, and they spontaneously form fibrils, assisted by remaining nonhelical telopeptides (1, 4). Evidently, collagen molecules themselves contain all the information needed for fibril assembly. Therefore, in physiological conditions, acid-solubilized collagen monomers form tissue-type long fibrils with characteristic axial periodic structure also in v...

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There is limited evidence suggesting that i.v. lidocaine may be a useful adjuvant during general anaesthesia because of its beneficial impact on several outcomes after surgery.

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