CYTOLYSOMES IN METABOLICALLY ACTIVE CELLS

Abstract

Ashford and Porter (1) have described membranelimited vacuoles in liver cells that contain mitochondria in a variety of degenerative states, fragments of endoplasmic reticulum, and granules. More recently, Novikoff and Essner (6) have demonstrated the presence of similar bodies in liver cells, and have shown them to be the site of acid phosphatase activity. In an earlier report, Novikoff (4) had observed them in the proximal tubule cells of the kidney. In the above reports, the tissues had been subjected to rigorous experimental procedures, i.e. the perfusion of isolated liver with glucagon (Ashford and Porter, 1) the intravenous injection of a detergent, Tri ton WR1339 (Novikoff and Essner, 6), or the ligation of the ureter (Novikoff, 4). Novikoff and Essner have stated that mitochondria-containing vacuoles are encountered only in pathological liver (similarly in pathological kidney), and, since these vacuoles occur in cells undergoing cytolysis, Novikoff has suggested the name cytolysome for them (5). Though both lysosomes and cytolysomes display acid phosphatase activity, Novikoff has pointed out that the typical lysosome of normal liver is smaller in size, more restricted in position, contains ferritin-like granules, and does not possess cytoplasmic inclusions. In a study of the changes in the fine structure of brown adipose cells rapidly mobilizing lipid, structures similar to cytolysomes have been encountered, and it seems useful to report their occurrence in a metabolically active, but not degenerate, tissue. Sidman and Fawcett (7), in light microscope studies, have shown that fasting mice, subjected to a cold-room temperature of 5°C, mobilize significant amounts of lipid from the interscapular fat pad. The mobilization of lipid was indicated by the depletion of cellular lipid inclusions, and was shown to be dependent upon the innervation of the fat pad. In the study in which the present observations were made, rats were fasted for 12 hours and then placed in individual cages in a cold room (5-7°C) with water ad libitum, but no food. After 6 hours of exposure, the animals were sacrificed by decapitation and the interscapular fat pads excised. Animals fasted for 18 hours and maintained at 21°C were used as controls. Blocks of tissue (1 X 1 × 2 mm) were fixed for 11~ to 2 hours in cold (4°C) phosphate-buffered 1 per cent osmium tetroxide, dehydrated in increasing concentrations of ethanol, placed in 3 changes of dry acetone (1~ hour each), and embedded in Vestopal W. Tissues were sectioned with a Porter-Blum or Huxley microtome, stained with lead hydroxide (2), and examined with either a Philips 100B