Site of action of a polyanion inhibitor of phagosome-lysosome fusion in cultured macrophages

Abstract The subcellular site of action of a new polyanionic inhibitor of phagosome-secondary lysosome fusion (P-LF) in cultured macrophages is described. This semi-synthetic compound chlorite-oxidized amylose (COAM) prepared from amylose starch differs from previously reported inhibitors by its rapidity in suppressing P-LF, and shows low toxicity and a wide range of effective dose. The inhibitor was conjugated to a fluorescent label or to an electron-opaque label and its subcellular location directly determined in living macrophages by fluorescence microscopy and in thin sections by electron microscopy. The fluorescent polyanion was seen only in secondary lysosomes. In cells containing both the fluorescent inhibitor and phagocytosed yeast cells there was no transfer of fluorescence to phagosomes, indicating inhibition of P-LF. The inhibition of fusion was reversed by low levels of lipophilic amines. The possibility that polyanions inhibit P-LF by acting on the lysosomal membrane is discussed.