Cellular Mechanisms of Protein Metabolism in the Nephron

Abstract

We have shown (1) that the droplets forming in the epithelial cells of the proximal convolution of the rat kidney after the administration of various proteins give a strongly positive supravital reaction with dilute Janus green. This observation indicates that they are not simple accumulations of the absorbed material and suggests that they are complex objects composed of a mixture of the absorbed protein and mitochondrial elements, the latter derived from the rodlets of the renal cells which were observed to disappear concomitantly with the formation of the droplets. From such a hypothesis it would follow that the enzymatic content of the mitochondria is thus brought into immediate contact with the substrate, absorbed protein, which is ultimately to be digested inside the cell. The prompt reduction of the dye within the droplet supported this assumption.The basis of these inferences is a staining reaction with a dye and its subsequent reduction in the droplet, and since the chemical or physical mechanisms involved in the reaction are unknown, more information is needed. It should, for example, be possible to demonstrate in the droplet those chemical substances which occur in the mitochondrial rodlets; the present study is an attempt to do so by means of the methods of histochemistry. The rigorous validity of many of these methods is open to question; some of them might better be termed more or less specific "staining reactions;" but these and other shortcomings have been thoroughly considered by others and are generally recognized. Our

Subcellular particles; a symposium held during the meeting of the Society of General Physiologists at the Marine Biological Laboratory, Woods Hole, Massachusetts, June 9-11, 1958

“…The relationship of these granules to 'athrocytosis'-a term which was actually invented to explain their origin -rests on a long line of morphological studies (see 37, 74, 70, 71), and these have been amply verified by the more recent biochemical in\estigations. Indications that the droplets contain the injected material have been obtained by Oliver, MacDowell, Moses and Lee (71) after the administration of proteins, and by Lee (61) and Kretchmer and Cherot (55) after the injection of amino acids. The segregation of egg white by the droplets was later demonstrated on purified fractions by Straus and Oliver (96) with the aid of a semic]uantitati\c serological method.…”

“…Oliver and his co-workers (70,71,61), and with the aid of electron microscopy by Rhodin (79) and by Gansler and Rouiller (36), who have also demonstrated the presence of smaller bodies of a similar type (big granules and microbodies)…”

Cellular Mechanisms of Protein Metabolism in the Nephron

“…The detail of the histochemical differences among the various droplets with which we shall be concerned in this study are shown in Table I; the methods used in these procedures have been given elsewhere (3,4). Since proteins are ubiquitous in protoplasmic structures, it is the intensity of the reaction which localizes a concentration of these bodies.…”