PHAGOCYTOTIC CELLS IN THE FISH HEART

Comparatively little is known about host-defense activities in the fis h heart. Investigations showed that intraperitoneally injected carbon particles are actively taken up by the cardiac endothelial cells of th e medaka Oryzias latipes, but less so by those of the goldfish Carassi us auratus and lemon tetra Hyphessobrycon pulchripinnis. (In vitro exp eriments confirmed these species differences in endocytic activities b y these cells.) Electron microscopy revealed that endothelial cells of the medaka atrium have large cytoplasm with many organelles, and inge sted carbon particles were observed within phagosomes of cardiac endot helial cells even at 4 degrees C. Phagocytic cells, which apparently r eside in the heart, were found in all the species examined. These cell s were located on the endothelial cells and developed cytoplasmic proc esses extending toward the heart lumen and/or the intercellular spaces of the endothelial cells. The heart with its resident phagocytes is p roposed to function as a host defense organ-at least in certain fish s pecies.