Abstract
Integrins are transmembrane receptors that mediate cell to substlate adhesion by forming links between the extracellular matrix and cytoskeleton. They participate in organizing cell adhesion sites and the actin-containing cytoskeleton, but also mediate signal transduction such as gene expression. Consequently integrins provide an intersection where mechanical forces, cytoskeletal organizations, biochemical signals and adhesions can meet. We wonder how a single receptor can fulfill the mechano-chemical signal transduction. To address this question, we first analyzed the distribution of individual integrin heterodimers in the ventral membrane of endothelial cells at ultrastructural level. To this end, immuno-freeze-etching-replica method (IFER) was applied to the exposed intracellular surface of the basal membrane prepared by a brief sonication. EM images stained with immuno-gold of integrins showed that there were many small sized (9.7 ± 9.3 ×10−3 μm2; mean ± SD) integrin aggregates in the region out of focal adhesion but near stress fibers. It should be noted that integrins in an aggregate seemed to be connected each other with fine filamentous structures. Moreover time-laps imaging of the integrin aggregates showed that some of them were very stable like as fixed points. This result suggests that the integrin aggregate may form an unknown type of fixed point at the basal membrane different from that at Focal adhesion. [Jpn J Physiol 54 Suppl:S70 (2004)]
