PRESERVATION OF THE FINE STRUCTURE OF ISOLATED LIVER CELL PARTICULATES WITH POLYVINYLPYRROLLIDONE-SUCROSE

The purpose of this brief communication is to illustrate the effectiveness of polyvinylpyrrollidone-sucrose in preserving the fine structure of cell particulates of rat liver during their isolation by homogenization and differential centrifugation. As reported elsewhere (1, 2), the medium we have evolved is a modification of those of Woods (3) and Greenfield and Price (4). I t is a mixture of 7.3 per cent polyvinylpyrrollidone (PVP) and 0.25 M sucrose, adjusted with alkali to pH 7.6-7.8. This yields a homogenate of pH 6.9-7.1. Phase-contrast microscopy shows that the mitochondria retain, for long periods of time, the typical rod shapes seen in the intact cell. Their biochemical integrity is well preserved, as indicated by the latency of their ATP-ase and their ability to carry on oxidative phosphorylation in the absence of fluoride (1, 2). For fixation, we have found a mixture of 7.3 per cent PVP, 0.25 ~ sucrose, and 2 per cent osmium tetroxide to be effective when adjusted to pH 7.0 (2). An unpurified fraction isolated from PVP-sucrose homogenate is shown in Fig. 1. This section is chosen because it includes different particulate types. The mitochondria (rot) show the typical outer and inner membranes, and small inner granules (5-8). Most noteworthy is the uniform density of such mitochondria. This indicates that little, if any, loss of material has occurred during isolation. The microsomal material (me, Fig. 1; also Fig. 2) shows a striking resemblance to the basophilic material seen within liver cells in sections (9, 7, 10, 11). Except for length, these microsomes appear identical with the granulecoated membranes of the ergastoplasm or endoplasmic reticulum (12-14, 10). Other cytoplasmic structures which are apparently well preserved when isolated from PVP-sucrose are Golgi membranes (g, Fig. 1) and the so-called "dense bodies" (db, Fig. 2; see also Novikoff et al. (15)). What appear to be microvilli of the bile canaliculi (m, Fig. 3) (9, 16, 11) and other membranes (me, Fig. 1) whose cytologic identity is not known are also present.