Addition of wortmannin to normal rat kidney cells caused a redistribution of the 
lysosomal type I integral membrane proteins Igp110 and Igp120 to a swollen 
vacuolar compartment. This compartment did not contain the cation independent 
mannose 6-phosphate receptor and was depleted in acid hydrolases. It was 
distinct from another swollen vacuolar compartment containing the cation 
independent mannose 6-phosphate receptor. The swollen Igp110-positive 
compartment was accessible to a monoclonal antibody against Igp120 added 
extracellularly, showing that it had the characteristics of an endosomal 
compartment. Wortmannin had no gross morphological effect on the trans-Golgi 
network or lysosomes nor any effect on the delivery to the trans-Golgi network 
of endocytosed antibodies against the type I membrane protein TGN38. We propose 
that the observed effects of wortmannin were due to inhibition of membrane 
traffic between cation independent mannose 6-phosphate receptor-positive late 
endosomes and the trans-Golgi network and to inhibition of membrane traffic 
between a novel Igp120-positive, cation independent mannose 6-phosphate 
receptor-negative late endosomal compartment and lysosomes. The effects of 
wortmannin suggest a function for a phosphatidylinositol 3-kinase(s) in 
regulating membrane traffic in the late endocytic pathway.