Distribution of chondrocytes containing alpha-smooth muscle actin in humanarticular cartilage

Relatively little is known about the contractile behavior of the human arti cular chondrocyte. Other connective tissue cells are known to express a con tractile actin isoform, alpha -smooth muscle actin, in response to injury, at selected stages of wound healing, and in certain pathological conditions . This and recent work demonstrating contractile behavior in adult canine a rticular chondrocytes in vitro prompted the present study of the distributi on of alpha -smooth muscle actin-containing chondrocytes in human articular cartilage. Approximately 75% of the chondrocytes in the superficial region of cartilage expressed alpha -smooth muscle actin as demonstrated by immun ohistochemistry. In contrast, only approximately 10% of the cells in the de ep region stained fur this contractile actin isoform. There was no correlat ion of the percentage of alpha -smooth muscle actin-positive cells in eithe r region with Mankin grade or with age. This is the first report of a contr actile potential for human articular chondrocytes. The roles of a-smooth mu scle actin in these cells warrant further investigation. The question of wh ether it is necessary to refer to these cells as myochondrocytes is conside red.