QUANTITATIVE STUDY OF IN RAT LIVER Dry Mass, Wet Mass, Volume, MITOCHONDRIA and Concentration of Solids

The dry mass, wet mass, and volume of mitochondria of normal rat liver were determined, as well as nitrogen content and concentration. A scheme of multiple approaches to these quantities was devised, permitting comparison of values obtained by independent methods. The following basic values are considered highly accurate: Mean dry mass, 13.6 X l0 -14 g; mean wet mass, 51.8 X 10 -14 g; mean volume, 0.43 /z3; nitrogen content, 1.75 X l0 -14 g The work emphasizes the fact that in mitochondria the quantities, mass, and volume occur in logarithmic-normal distributions. I N T R O D U C T I O N In 1959, Noyes and Smith (9) reported early, dramatic changes in liver mitochondria of rats that had received 1000 r of whole-body irradiation. The mass of individual mitochondria, isolated by differential centrifugation, was found to be almost doubled. Small mitochondria appeared to be preferentially fragmented. Meanwhile the total nitrogen content of the liver tissue as a whole remained essentially unchanged. Normal values of mitochondrial mass were reestablished after only a few hours of recovery. This solitary report on early quantitative mitochondrial changes as a consequence of irradiation led us to repeat the experiments with the intent of studying the radiosensitivity of the chondriome in greater detail and with refined methods. Reinvestigation appeared the more desirable inasmuch as Scaife and Alexander (10) reported no appreciable sensitivity of mitochondria to irradiation in experiments in vitro. Studies of normal mitochondria and of experimentally altered mitochondria are usually done by means of biochemistry and /o r electron microscopy. The subtle detail of chemical information provided by biochemistry is, however, limited by the fact that it deals by necessity with average values. Morphological studies at the resolution of the electron microscope tend to render rather detailed information on a severely limited sample volume. Singly or jointly, these approaches did not seem to offer direct means for the effective study of populations of mitochondria in terms of the findings of Noyes and Smith. In view of the fact that desirable absolute data, particularly on objects as small as mitochondria, obtained by any method employed cannot be proved reasonably correct unless confirmed or corroborated by results from an independent, methodologically different technique, it was necessary to devise a scheme of multiple experimental approaches to the fundamental quantities of individual mitochondria in populations of the organelle. These quantities are dry (wet) mass, volume, and corwentration of solids. Only one method each was available for deter507 on O cber 9, 2017 jcb.rress.org D ow nladed fom COULTER PARTICLE COUNTER I" I MORPHOLOGICAL I I QUANTITATIVE i CONTROL t ELECTRON I I . . . . . . . .J MICROSCOPY I