Gap junctions in human synovial cells and tissue

Our objective was to establish the existence of intercellular communication through gap junctions in synovial lining cells and in primary and passaged cultures of human synovial cells. Communication between cells was assessed using the nystatin perforated-patch method, fluorescent dye transfer, immu nochemistry, transmission electron microscopy, and immunoblotting. Function al gap junctions were observed in primary and passaged cultures and were ba sed on measurements of the transient current response to a step voltage. Th e average resistance between cells in small aggregates was 300 +/- 150 M Om ega. Gap junctions were also observed between synovial lining cells in tiss ue explants; the size of the cell network in synovial tissue was estimated to be greater than 40 cells. Intercellular communication between cultured c ells and between synovial lining cells was confirmed by dye injection. Punc tate fluorescent regions were seen along intercellular contacts between cul tured cells and in synovial membranes in cells and tissue immunostained for connexin43. The presence of the protein was verified in immunoblots. Regul ar 2-nm intermembrane gap separations characteristic of gap junctions were seen in transmission electron micrographs of synovial biopsies. The results showed that formation of gap-junction channels capable of mediating ionic and molecular communication was a regular feature of synovial cells, both i n tissue and in cultured cells. The gap junctions contained connexin43 prot ein and perhaps other proteins. The physiological purpose of,a a: junctions in synovial cells is unknown, but it is reasonable to anticipate intercell ular communication serves some presently unrecognized function. J. Cell. Ph ysiol. 184:1 10-117, 2000. (C) 2000 Wiley-Liss. Inc.