Aberrant Mitochondria with Longitudinal Cristae Observed in the Normal Rat Hepatic Parenchymal Cell. Takuma Saito and Kazuo Ozawa

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1 Okajimas Fol. anat. jap., 44 : , 1968 Aberrant Mitochondria with Longitudinal Cristae Observed in the Normal Rat Hepatic Parenchymal Cell By Takuma Saito and Kazuo Ozawa Department of Anatomy, Kansai Medical School Moriguchi, Osaka, Japan It is the aim of the present short communication to report aberrant mitochondria having longitudinal cristae encountered in the hepatic parenchymal cell in the normal albino rat. Material and Method Material used was liver of the normal adult albino rat weighing _approximately 150 g. The tissue excised from the rat killed by a blow on the neck was fixed in 2% glutaraldehyde in 0.1 M cacodylate buffer, ph 7.2, containing 8% sucrose (S a b a t i n i et al., 1963), for 1 hour.at 0-4 C, washed overnight in 0.1 M cacodylate buffer, ph 7.2, with.8% sucrose, refixed in buffered osmium tetroxide (C a u 1 f iel d, 1957) for 1 hour at 0-4 C, dehydrated through graded alcohols and propylene oxide, and embedded in epon (L u f t, 1961). Thin sections were made with a LKB ultrotome, mounted directly on 400-mesh grids, stained with uranium (W a t s o n, 1958) and/or lead (R e y n o 1 d s, 1963), and observed under the JEM-7 electron microscope. Photographs were taken at direct magnifications of 5,000 to 20,000. Results Among normal mitochondria having transverse cristae to the long axis, few aberrant mitochondria with longitudinally oriented cristae were observed in the hepatic parenchymal cell (Figs. 1 and 2). Aberrant mitochondria were slender, although slightly curved, in shape and measured approximately 0.1p in width and 1.5 to 3.0p in length. Slight bulgings were formed at both extremities, where some cristae ran obliquely. The internal mitochondrial membranes showed some tendency of beaded appearance in some areas. The matrix in aberrant 357

2 358 Takuma Saito and Kazuo Ogawa mitochondria was as dense as in normal mitochondria. A few inframitochondrial granules were also observed in the matrix of some aberrant mitochondria. It was of interest to find the thin tubular structures closely associated with aberrant mitochondria (arrows in Fig. 2). These tubules somewhat resembled the longitudinal cristaeseen in aberrant mitochondria. Some of the tubules seemed to have connection with the rough-surfaced endoplasmic reticulum, though not convincing (at site marked x in Fig. 2). Discussion Mitochondria with longitudinal cristae have been described in neuroglial cells and their processes (Type c mitochondria) (G r a y, 1960), spermatozoids (mitochondries aberrantes) (A n d r é, 1962) and the proximal convoluted tubule of the frog kidney in the winter (K a r n o v s k y, 1963). However, in mitochondria usually encountered in normal rat hepatic parenchymal cell the cristae, which are relatively scanty and irregular in occurrence, are oridinarily transverse to the long axis of mitochondria, and the slender mitochondria with longitudinal cristae observed in the present investigation can be considered "aberrant mitochondria " in the rat hepatic parenchymal cell. Recently much evidences showing the direct functional-structural relationship in mitochondria have been accumulated and it seems to be true that functional alterations in metabolic activity is accompanied by visible changes in the fine structure of mitochondria (L ehni n- ger, 1964; De Robertis et al., 1965; Fawcett, 1966). Since it has been shown that mitochondria having longitudinal cristae do not swell significantly (L ehninge r, 1964), aberrant mitochondria seen in the liver may have something to do with swelling-contraction mechanism in connection with respiration. In fact, mitochondria with longitudinal cristae seem to have low oxidative enzymatic activity as reported in the frog kidney by K a r n o v sky (1963). Thus, there is a possibility that aberrant mitochondria observed in the hepatic parenchymal cell represent a hypofunctional phase of mitochondria in terms of the oxidative respiration. In addition to this, however, there exist alternative explanations such as follows. In the first place, since aberrant mitochondria are somewhat stretched in particular at the mid-portion, it is not unlikely that they may represent a certain stage of mitochondrial division by the mechanism similar to an amitotic division of the cell. Secondly, the very intimate topographic relationship of the tubular structure, perhaps a variant of the smooth-surfaced

3 Aberrant Mitochondria with Longitudinal Cristae 359 endoplasmic reticulum, with aberrant mitochondria should not be overlooked. In mitochondria having longitudinal cristae observed in other cases (G r a y, 1960; Andr 6, 1963; Karnovsk y, 1963) there was no close contact of tubules with mitochondria. The close relationship with tubules is rather specific in aberrant mitochondria observed in the present investigation. It may imply the existence of a certain metabolic interrelationship between two organelles. However, taking into consideration of the structural similarity of tubules with longitudinal cristae and of the probable connection of tubules with the rough-surfaced endoplasmic reticulum, a possibility that the intimate relationship of two organelles suggests a certain feature of mitochondriogenesis from the endoplasmic reticulum may not entirely be improbable. Summary Aberrant mitochondria having longitudinal cristae encountered in the hepatic parenchymal cell of the normal adult albino rat were reported. The functional significance of aberrant mitochondria was briefly discussed. References Andre, J.: Contribution a la connaissance du chondriome. J. Ultrastr. Res., Suppl. 3: 1-185, Caulfield, J.B.: Effects of varying the vehicle for 0s04 in tissue fixation. J. Biophys. Biochem. Cytol., 3: , De Robertis, E.D.P., W.W. Nowinski and F.A. Saez: Cell Biology. W.B. Saunders Co., Philadelphia, F a w c e t t, D. W.: The Cell. Its Organelles and Inclusions. An Atlas of Fine Structure. W. B. Saunders Co., Philadelphia, Gray, E.G.: Regular organisation of material in certain mitochondria of neuroglia of lizard brain. J. Biophys. Biochem. Cytol., 8: , Karnovsk y, M. J.: The fine structure of mitochondria in the frog nephron correlated with cytochrome oxidase activity. Exp. Molec. Path., 2: , Lehninge r, A. L.: The Mitochondrion. Molecular Basis of Structure and Function. W. A. Benjamin, Inc., New York, L u f t, J. H.: Improvements in epoxy resin embedding methods. J. Biophys. Biocheṃ Cytol., 9: , Reynold s, E. S.: The use of lead citrate at high ph as an electron opaque stain in electron microscopy. J. Cell BioL, Ii: , Sabatini, D. D., K. Bensch and R. J. Barrnett: Cytochemistry and electron microscopy. The preservation of cellular ultrastructure and enzymatic activity by aldehyde fixation. J. Cell Biol., 11 : 19-57, W a t so n, M. L.: Staining of tissue sections for electron microscopy with heavy metals. J. Biophys. Biochem. Cytol., 4: , 1958.

4 360 Takuma Saito and Kazuo Ogawa Explanation of Figures Fig. L Rat hepatic parenchymal cell. Aberrant mitochondria having longitudinal cristae are observed in the center. x 23,000 Fig. 2. Aberrant mitochondria. The intimate relationship of tubular structures (arrows) with aberrant mitochondria can be seen. The tubular structures, probably a variant of the smooth-surfaced endoplasmic reticulum, seem to have connection with the rough-surfaced endoplasmic reticulum at site marked x. x 62,000

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6 363 Plate T. Saito and K. Ogawa II