Pericanalicular location of hepatocyte lysosomes and effects of fasting: a morphometric analysis

Lysosomes constitute a small proportion of hepatocyte volume, but they play a key degradative role, particularly during catabolic states such as nutritional deprivation. Our preliminary observations in hepatocytes suggested that fasting may alter the distribution of lysosomes, which are thought to congregate about the biliary canaliculus. The current study aimed to provide, in both fed and fasted rats, a quantitative morphometric analysis of lysosomes in the immediate pericanalicular and successively more distant regions. We selected three regions of radius 0 to 2 (region 1), 2 to 4 (region 2) and 4 to 6 micron (region 3) about the bile canaliculus and compared lysosomal numerical and volume densities. In fed rats, numerical and volume densities of both primary and secondary lysosomes were 5 to 10 times greater in region 1 than in region 3. After a 72-hr fast, this gradient was lost due largely to a reduced number of primary and secondary lysosomes in region 1. Our calculations suggest that during fasting, lysosomes are redistributed away from the bile canaliculus towards the more distant cytoplasm rather than being lost from the cell, for example, into bile. The number of overt macroautophagic vacuoles was not altered by fasting. We estimate that, in fed rats, there are approximately 270 lysosomes per hepatocyte, and that 43% of lysosomes are contained in the immediate pericanalicular region 1, which comprises only 7 to 8% of the cytoplasmic volume. The reason for this pericanalicular concentration of lysosomes and the mechanism of the redistribution with fasting remain to be determined.