FINE STRUCTURE OF LIPID GRANULES IN PROXIMAL TUBULE CELLS OF MOUSE KIDNEY

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Abstract
In electron microscopic investigations on the proximal tubule of the mouse kidney, large osmi- ophilic granules in the cytoplasm of the epithelial cells have been found by various authors (2, 13, 14, 20). Rhodin (13) and Clark (2) have pointed out that the granules contain concentric lamellae, but there have been no further investigations on the fine structure of these granules so far. Recently Miller (10) described granules which show a regu- lar pattern of layered dense and light bands with a repeating period of about 80 to 90 A. In our electron microscopic investigations on the proxi- mal tubule cells of the kidney/we observed similar granules which show in some respects a different structure. The granules which will be described were found in almost every epithelial cell of the proximal tubule, chiefly in the apical and intermediate zones of the cell. In one of three animals examined, every cell in one section contained 3 to 15 gran- ules; in the other two animals there were only 1 to 2 granules in each cell. This difference did not appear to be related to any specific physiological condition. All granules seen were of the same type. The granules have a round, oval, or com- pletely irregular profile (diameter 0.3 to 1.2 /z). They are surrounded by a one-layered membrane about 20 to 40 A thick and of medium density (Fig. 1), whereas Miller (10) described a mem- brane 60 A thick. Between this membrane and the outer lining of the granule itself there is a light space which is, on the average, 23 A wide. The granules regularly show at their outer periphery a i Kidney cortex of three normal mice (weight 15 to 20 gm) was fixed for I hour in 1 per cent buffered (pH 7.3), isotonic OsO4 solution without additional contrasting. The specimens were embedded in Vestopal W (1 per cent initiator, 0.5 per cent acti- vator) polymerized at 60°121 (8). Thin sections were prepared with a Porter-Blum microtome. Electron micrographs (including focal series) were taken with the Siemens Elmiskop I at 80 kv. thin rim of very dense granular material. In the interior of the granules two basic patterns can be discerned for descriptive purposes: a) An "ordered pattern" (Figs. l, 2 a): This consists of parallel, alternating dense and light bands, the center-to-center distance between two adjacent dense or light bands being 40 to 45 A (average 43 A). The dark bands appear some- what narrower than the light ones and have an average width of 16 A, making the average width of the light bands about 27 A. Up to 33 parallel dense and light bands could be observed, forming a striped and concentrically arranged pattern. This ordered pattern is found in most cases. In a few granules it appears to be not quite so regular, because the dense bands show a somewhat un- dulating course and therefore the distances be- tween them vary and the concentric band pat- tern appears frayed.