Fig. 2. Free ATP and lactate levels of wild-type and mutant chondrocytes cultured under normoxia and 22 hours hypoxia. (A) Bars representing means ± standard deviations of free ATP-levels measured in three independent experiments, normalized to protein content. Free ATP levels were determined in mutant and wild-type cultures under normoxia and hypoxia. (B) Lactate levels in supernatants of wild-type chondrocytes cultured at 0.5% oxygen were significantly increased compared with normoxic levels. Reduced lactate concentrations were detected in supernatants of HIF-1-null chondrocytes under normoxia and hypoxia. Bars are representing the means ± standard deviations of measured triplicates from three independent experiments, normalized to protein concentrations. Statistical differences were calculated as: wild-type normoxia vs HIF-1-null normoxia; wild-type hypoxia vs HIF-1-null hypoxia; wild-type normoxia vs wild-type hypoxia. *P0.05; **P0.01.