ABSTRACT
Lysosomes mediate a range of biological processes, such as the degradation of macromolecules, plasma membrane repair, regulation of cellular metabolism and immune response. In this chapter, the authors describe different methods to study lysosomal Cl¯ concentration and permeability, highlighting their principles of operation, advantages and disadvantages. They discuss how these measurements have advanced our understanding about the role of lysosomal Cl¯. Assays using isolated lysosomes are suited to measure ionic fluxes across lysosomal membranes, but cannot be used to determine native steady-state ion concentrations because these are likely to change during the purification procedure. Acidification of the lysosomal lumen is directly mediated by a V-type proton ATPase, which needs, however, parallel anion or cation conductive pathways to allow bulk proton transport by compensating the electric charge transported by the ATPase. The difficulties to obtain pure lysosomal preparations also limit the study of ion fluxes with isolated lysosomes.
