DIFFERENT MECHANISMS ARE INVOLVED IN INTRACELLULAR CALCIUM INCREASE BY INSULIN-LIKE GROWTH-FACTOR-1 AND GROWTH-FACTOR-2 IN ARTICULAR CHONDROCYTES - VOLTAGE-GATED CALCIUM CHANNELS, AND OR PHOSPHOLIPASE-C COUPLED TO A PERTUSSIS-SENSITIVE G-PROTEIN/

This study describes the mechanisms involved in the IGF-1 and IGF-2-in duced increases in intracellular calcium concentration [Ca2+](i) in cu ltured chondrocytes and the involvement of type 1 IGF receptors. It sh ows that IGF-1, IGF-2, and insulin increased the cytosolic free calciu m concentration [Ca2+](1) in a dose-dependent manner, with a plateau f rom 25 to 100 ng/ml for both IGF-1 and IGF-2and from 1 to 2 mu g/ml fo r insulin. The effect of IGF-1 was twice as great as the one of IGF-2, and the effect of insulin was 40% lower than IGF-1 effect. Two differ ent mechanisms are involved in the intracellular [Ca2+](i) increase. 1 ) IGF-1 and insulin but not IGF-2 involved a Ca2+ influx through volta ge-gated calcium channels: pretreatment of the cells by EGTA and verap amil diminished the IGF-1 or insulin-induced [Ca2+](i) but did not blo ck the effect of IGF-2. 2) IGF-1, IGF-2, and insulin also induced a Ca 2+ mobilization from the endoplasmic reticulum: phospholipase C (PLC) inhibitors, neomycin, or U-73122 partially blocked the intracellular [ Ca2+](i) increase induced by IGF-1 and insulin and totally inhibited t he effect of IGF-2 This Ca2+ mobilization was pertussis toxin (PTX) de pendent, suggesting an activation of a PLC coupled to a PTX-sensitive G-protein. Lastly, preincubation of the cells with IGF(1) receptor ant ibodies diminished the IGF-1-induced Ca2+ spike and totally abolished the Ca2+ influx, but did not modify the effect of IGF-2. These results suggest that IGF-1 action on CA(2+) influx involves the IGF(1) recept or, while part of IGF-1 and all of IGF-2 Ca2+ mobilization do not impl icate this receptor. (C) 1997 Wiley-Liss, Inc.