Ultrastructural localisation of acid phosphatase in intestinal eosinophilic granule cells (EGC) of rainbow trout (Oncorhynchus mykiss) following degranulation with capsaicin

Enzyme cytochemistry was used to investigate possible lysosome involvement in capsaicin induced degranulation of the eosinophilic granule cell (EGC) of the rainbow trout intestine. Three adult rainbow trout (Oncorhynchus mykiss) were injected intraperitoneally with capsaicin in a saline vehicle (0.5 micrograms.g-1 body weight). Following a 2 hour period of incubation, the fish were killed, and a mid portion of the intestine was dissected and fixed in cold glutaraldehyde buffered with sodium cacodylate. Vibratome sections were incubated in either reaction medium containing beta-glycerophosphate and cerium chloride in acetate buffer or substrate (beta-glycerophosphate) deficient control medium. Sections were then refixed in osmium tetroxide and processed for electron microscopy. Acid phosphatase was found to be localised within lysosomes. The enzyme was not found in the large cytoplasmic granules under normal or capsaicin-stimulated conditions. EGCs which had migrated to the lamina propria in response to the capsaicin stimulation had a distinct multivesicular granule morphology. These multivesicular granules did not contain acid phosphatase suggesting that this form of EGC degranulation is not a lysosomally mediated event.