Decrease in cytosolic free Ca2+ and enhanced proteoglycan synthesis induced by cartilage derived growth factors in cultured chondrocytes

Cartilage-derived growth factors, enhance proteglycan synthesis in cultured chick-embryo chondrocytes, and have almost no effect on cell proliferation. Addition of carilage derived growth factors to cartilage cells loaded with the fluorescent Ca 2+ indicator quin 2, caused a rapid, concentration dependent decrease in cytoplasmic free Ca 2+ . This decrease persisted also in Ca 2+ -free medium, indicating that it is not mediated by a decrease in the passive permeability of cell membrane to Ca 2+ . Addition of the Ca 2+ ionophore A23187, with or without cartilage derived factors, caused an increase in cytoplasmic free Ca 2+ together with inhibition of proteoglycan synthesis and enhanced cell proliferation. The results may indicate that whereas cell proliferation in chondrocytes is signaled by an increase in cytoplasmic Ca 2+ ([Ca 2+ ] in ), proteoglycan synthesis is signaled by a decrease in [Ca 2+ ] in . The data lead to suggesting a mechanism for antagonistic regulation of cell proliferation and the expression of the differentiated state.