The intralysosomal pH in cultured human skin fibroblasts in relation to cystine accumulation in patients with cystinosis

The intralysosomal pH in cultured skin fibroblasts from a patient with cystinosis and from control fibroblasts was estimated by the method of Hollemans et al. (Hollemans, M., Oude Elferink, R.P.J., de Groot, P.G., Strijland, A. and Tager, J.M. (1981) Biochim. Biophys. Acta 643, 140-151). 1. The intralysosomal pH in cystinotic fibroblasts (5.37 +/- 0.04; n = 12) was almost identical to that in the control fibroblasts (5.27 +/- 0.06; n = 10). 2. After depletion of cystine by pretreatment of cystinotic fibroblasts with 1 mM cysteamine, there was no significant change in the intralysosomal pH. Incubation of either cystinotic or control fibroblasts with higher concentrations of cysteamine (10 or 25 mM) led to an increase in intralysosomal pH similar to that seen with other weak bases. 3. The fractional volume of the lysosomes in cystinotic fibroblasts (0.100 +/- 0.012; n = 4) was higher than that in control fibroblasts (0.039 +/- 0.010; n = 4). 4. It is concluded, in contrast to Jonas et al. (Jonas, A.J., Smith, M.L. and Schneider, J.A. (1982) J. Biol. Chem. 257, 13185-13188), that the lysosomal proton-translocating ATPase (Okhuma, S., Moriyama, Y. and Takano, T. (1982) Proc. Natl. Acad. Sci. USA 79, 2758-2762) is not impaired in cystinotic fibroblasts