Synthesis of ultrasmall water-soluble fluorescent gold nanoclusters is reported. The clusters have a decent quantum yield, high colloidal stability, and can be readily conjugated with biological molecules. Specific staining of cells and nonspecific uptake by living cells is demonstrated.

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Abstract-Gap-junctional intercellular communication in endothelial cells is implicated in the coordination of growth, migration, and vasomotor responses. Up to 3 connexin types, connexin40 (Cx40), Cx37, and Cx43 may be expressed in vascular endothelium according to vascular site, species, and physiological conditions. To establish how these connexins are organized at the level of the individual endothelial gap junction, we used affinity-purified connexinspecific antibodies raised in 3 different species to permit double and triple immunolabeling in combination with confocal and electron microscopy. Using HeLa cells transfected with Cx37 and Cx40 for characterization, the anti-Cx37 antibody (raised in rabbit) and the anti-Cx40 antibody (raised in guinea pig) were shown to recognize single bands of 37 and 40 kDa, respectively, on Western blots and to give prominent punctate labeling at the cell borders, specifically in the corresponding transfectant. By applying these antibodies together with mouse monoclonal anti-Cx43 for double and triple immunofluorescence labeling at confocal microscopy, rat aortic and pulmonary arterial endothelia were found to express all 3 connexin types, whereas coronary artery endothelium expressed Cx40 and Cx37 but lacked Cx43. Key Words: gap junction Ⅲ connexin Ⅲ endothelium Ⅲ immunoconfocal microscopy Ⅲ freeze-fracture cytochemistry C oordination of cellular responses at the endothelial interface between the blood and underlying tissues is mediated by multiple signaling mechanisms, including direct intercellular communication via gap junctions. Among the functions in which endothelial gap-junctional intercellular communication has been implicated are the migratory behavior of endothelial cells after injury, angiogenesis, endothelial growth and senescence, and the coordination of vasomotor responses. 1-5 Gap junctions comprise clusters of transmembrane aqueous channels linking the cytoplasmic compartments of neighboring cells. 6 -8 These channels, insulated from extracellular space, provide electrotonic and metabolic pathways for the direct cell-to-cell transfer of small-signaling molecules and ions. Each channel is made from 2 connexons, 1 contributed from each of the partner cells, with each connexon comprising a hexamer of 6 connexin molecules. The connexins belong to a multigene family of related proteins, at least 13 members of which have been identified in mammals. 6,9 Many cell types and tissues are now documented as expressing more than 1 connexin type, and functional studies using in vitro expression systems indicate that gap junction channel properties differ according to the component connexin present. 7,9 -13 Multiple expression of connexins in a given tissue or cell type could in theory result in different populations of gap junctions, each containing a single connexin type, or gap junctions in which mixtures of connexins are present in the form of heterotypic channels, different types of homotypic channels, or heteromeric channels. 6,9 In view of the disparate channel prope...

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We have been investigating the fluorescent property and biocompatibility of novel fluorescent gold nanoclusters (FANC) in human aortic endothelial cells (HAEC) and endothelial progenitor cells (EPC). FANC (50-1000 nmol/L) was delivered into cells via the liposome complex. The fluorescence lasted for at least 28 days with a half-life of 9 days in vitro. Examination of 12 transcripts regulating the essential function of endothelial cells after a 72 h delivery showed that only the vascular cell adhesion molecule 1 and the vascular endothelial cadherin were down-regulated at high concentration (500 nmol/L). In addition, no activation of caspase 3 or proliferating cell nuclear antigens was detected. 3-[4,5-Dimethylthiazol-2-yl]-2,5- diphenyltetrazolium bromide (MTT) assay demonstrated that, unlike the markedly suppressed viability in cells treated with quantum dots, FANC had minimal effect on the viability, unless above 500 nmol/L, at which level a minor reduction of viability mainly caused by liposome was found. Tube formation assay showed no impaired angiogenesis in the EPC treated with FANC. In vivo study using hindlimb ischemic mice with an intramuscular injection of FANC-labeled human EPC showed that the cells preserved an angiogenic potential and exhibited traceable signals after 21 days. These findings demonstrated that FANC is a promising biocompatible fluorescent probe.