Integrated stereological and biochemical studies of hepatocytic membranes. I. Membrane recoveries in subcellular fractions

Previous attempts to relate the structure and function of hepatocytic membranes have compared biochemical data of fractions to morphological data derived from either intact tissue or fractions. The effects of the original homogenization aside, biochemical recoveries comparing membrane marker enzymes of the homogenate to subsequent fractions suggest a general conservation of activity. A sterological study was undertaken to estimate membrane surface areas in the intact tissue, homogenate, and fractions of the same livers and then to test the comparability of these data with membrane marker enzymes by calculating both morphological and biochemical recoveries. The sterological data were corrected for errors due to section thickness and compression. The average total membrane sufrace area per 1 g of liver was 9.3 m2 in the intact tissue (T), 7.8 m2 in the homogenate (H), and 7.4 m2 in the fractions (F); recoveries for the membrane surface areas thus averaged 96% for the (F/H) and 81% for the (F/T) comparisons. In homogenate and fractions, the differentiability of membranes by morphological criteria was limited to rough- and smooth- surfaced membranes, as well as outer and inner mitochondrial membranes. The recoveries of rough-surfaced membranes were 101% for F/H and 92% for F/T; those of smooth-surface membranes were 89% for F/H and 107% for F/T. For mitochondrial membranes, a recovery of 100% for F/H was obtained, whereas it amounted to only 54% for F/T. With respect to F/H, the membrane recoveries compare well with the marker enzyme recoveries obtained biochemically. The extension of recovery calculations to the intact tissue (F/T) revealed satisfactory conservation of the procedures of homogenization and fractionation; it indicates, however, that a shift of a substantial part of mitochondrial membranes to the pool of unidentifiable smooth membranes may occur on homogenization.