Figure 6

Influence tBHP on thapsigargin-induced changes in cytosolic calcium concentrations in CHO-M3 cells measured in the presence and absence of extracellular calcium (2 mM). Thapsigargin (1 μM) was added at the time indicated by the first arrow. Calcium concentration was determined following a 90 min exposure to the indicated concentrations of tBHP. Each line is the average response from 21–23 cells from two experiments; six replicate experiments yielded similar results. Thapsigargin-induced changes in cytosolic calcium concentrations were measured in the presence (a) and absence (b) of extracellular calcium. Calcium was reintroduced to the extracellular medium at the point indicated by the second arrow in b (final concentration = 2 mM). Cytosolic calcium levels measured 100 sec after exposure to thapsigargin were significantly lower in the presence of any concentration of tBHP (0.5- 20 mM), although the levels following exposure to the different concentrations of tBHP were not different from each other (ANOVA and Tukey’s test; p < 0.05, N = 6). Similarly, calcium levels 100 sec following reintroduction of calcium following thapsigargin treatment in absence of extracellular calcium (b) were significantly lower in the presence of any concentration of tBHP (0.5- 5 mM) (ANOVA and Tukey’s test; p < 0.05, N = 6), although the levels following exposure to the different concentrations of tBHP were not different from each other.