“…The calcium 23 APRIL 1982 concentration in the CF strains increased significantly between passages 7 and 14 (P < .0005), after which a plateau was reached (12). When cellular calcium in both groups reached a plateau (passages 14 to 20), the mean calcium concentration was 50 percent greater in CF (0.57 ± 0.02 p,g of calcium per milligram of ash, N = 5) than in control (0.38 + 0.01 ,ug of calcium per milligram of ash, N = 4) strains (P < .0005) (13). These experiments did not enable us to distinguish, as the cells aged, between increased calcium in all or most cells of the monolayer or -an increase in the proportion of cells with a higher cellular calcium content.…”