Experimental Lipogenesis by Purkinje Fibers

The heart of most animals contains a structure, believed to be a conduction system, extending from the sino-atrial node to beneath the endocardium of the ventricles. This structure is variably differentiated in different species. In ungulates it is conspicuous and consists of specialized muscle cells, called Purkinje fibers, set in fairly well defined bundles of loose connective tissue with an unusual amount of elastic tissue and nerve fibers. The Purkinje fibers differ morphologically from the rest of the cardiac muscle in being larger, having a less dense sarcoplasm, often with double nuclei, and in appearing on cross-section to have an unstained center to the individual fibers. In other species including man, rabbit, and dog the conduction system may be so inconspicuous as to raise the question whether it exists or not (6). For our purposes it is sufficient to state that the conduction system has been studied in a variety of species (although not heretofore in small animals) and has been especially well illustrated in sheep (8). Aside from its morphologic features, the Purkinje fibers may often be differentiated by a greater content of glycogen (8, 7) and of potassium (7) suggesting a carbohydrate and cationic metabolism distinct from that of the rest of the heart. They are also said to have a high cholinesterase content (2). The purpose of the present article is to describe another feature of the Purkinje system suggesting a distinctive fat metabolism. Specifically, the Purkinje fibers appear to have a capacity to synthesize sudanophilic fat when incubated in serum or serum supplemented by oleic acid, a capacity not shared by other cardiac muscle. The phenomenon of synthesis of sudanophilic fat by non-adipose tissue has been called aberrant lipogenesis (3). It is a property of many, although not all, cell types and depends on the presence of: (1) an intracellular sulfhydryl-dependent enzyme system; (2) serum; and (3) oleic acid or sodium oleate. Aberrant lipogenesis may be demonstrated in vivo by injecting oleic acid into tissues, but it is