Immunocytochemical and cytochemical demonstration of a novel selective lysosomal pathway (SLP) of secretion in the exocrine pancreas.

The intracellular distributions of lysosomal and zymogen granule (ZG) membrane proteins were analyzed in the pancreas exocrine acinar cell by cytochemical and immunocytochemical approaches. A strong signal was observed with acid phosphatase (AcPase) in the trans-Golgi network and condensing vacuoles, whereas mature ZG and acinar lumina were devoid of any detectable reaction. The enzyme appears to exit from the regulated pathway by a shedding process during conversion of condensing vacuoles to mature granules. Trimetaphosphatase (TMPase) shows no reaction in the Golgi apparatus and condensing vacuole but is present in immature granules. The exit from the regulated pathway appears to occur at a later stage of the ZG maturation process. A third lysosomal enzyme, nicotinamide adenine dinucleotide phosphohydrolase (NADPase), was found in the median cisterna of the Golgi stack, was undetectable in condensing vacuoles and ZG, but produced a strong signal in the acinar lumen. Our observations show that only one t...