Figure 3. Effect of inhibiting PLC on protein kinase C (PKC) activity in resting zone (RC) and growth zone (GC) chondrocytes. Confluent, fourth-passage RC cells were treated with 10^-7 M 24R,25-(OH)₂D₃ for 90 min (left panel), and GC cells were treated for 9 min with 10^-8 M 1,25-(OH)₂D₃ (right panel) in the presence or absence of the phospholipase C inhibitor U73122 (10 µM). At harvest, PKC specific activity in the cell layer was determined. Data represent the mean ± SEM of 6 cultures from one of two experiments yielding comparable results. *P < 0.05, treatment vs. control; •p < 0.05, U73122 vs. no U73122.