LIVER ULTRASTRUCTURE AND A NEW CELL TYPE IN THE JAPANESE NEWT, Cynops pyrrhogaster

The liver of the Japanese newt, Cynops pyrrhogaster, has been investigated using light, scanning, and transmission electron microscopy. Hepatic paren chyma was composed exclusively of clusters, cords and tubules of polyhed ral cells separated by a sinusoidal net. Hepatocytes had spherical, euchroma tic nuclei with one or more nucleoli and stacked mitochondria with an electron-dense matrix and sparse cristae. Rough endoplasmic reticula formed peribiliary stacks and diffusely scattered vesicles and tubules. Smooth endoplasmic reticula were more pronounced in glycogen-rich hepatocytes. Small, peribiliary Golgi complexes and peroxisomes were present. Most hepatocytes contained large numbers of fat droplets distributed evenly throughout the cytoplasm along with glycogen. Some cells were mainly glycogen-storing and contained few or no liposomes. Bile canaliculi had
Dept. of Biomedical Sciences, Virginia-Maryland Regional College of Vet. Med., Virginia Polytechnic Institute and State Univ. Blacksburg, Virginia, USA, 24061. Dept. of Biology, Yokohama City University, 22-2, Seto, Kannazawa-Ku, Yokohama,
short, stout microvilli which were entirely atretic in some canaliculi. Canaliculi were sealed off by junctional complexes including zonulae occludentes and maculae adherentes. The latter showed extraordinary wider desmosomal gaps in the vicinity of the atretic bile canaliculi. The sinusoid wall was lined with fenestrated endothelial cells connected to Kupffer cells by zanulae occludentes. Both the sinusoidal lining and adjacent hepatocytes were void of basal laminae.
A distinctive new cell type was observed in the newt liver. These cells were found individually or in small clusters in proximity with the sinusoidal surfaces. They had small nuclei, a paucity of cytoplasmic organelles, but numerous, unique, osmiophilic granules of two distinct types. Less numerous Type 1 granules contained homogenous electron dense material, and a predominant Type Il granule contained circum ferentially arranged subparticulation. Granules of both types were detec ted within the cytoplasm of endothelial cells and within sinusoids to gether with blood elements. The function of this secretory type cell remains obscure.