Experimental studies of the shape and structure of isolated cardiac jelly.

The properties of the early chick embryonic heart cardiac jelly were studied. The cells of the heart were removed by sequential treatments with calcium magnesium-free medium; the same medium containing 5 mM EDTA; and aqueous 0.1% deoxycholate. The transparent, naked cardiac jelly retained the original shape and size of the untreated original heart when immersed in physiological ionic strength medium. Its size and shape responded to changes in the ionic strength of the surrounding media. Alcian blue, cetylpyridinium chloride and testicular hyaluronidase abolished the ability of the jelly to respond to ionic strength changes. Electron microscope examination of the negatively stained spread cardiac jelly revealed an extensive network of collagenous fibrils and fine filaments with some amorphous adhering material. Treatment with testicular hyaluronidase removed much of the amorphous material and improved the details of the filaments. These results suggest that glycosaminoglycans play an important part in the hydration of the cardiac jelly and that the stability of the cardiac jelly shape is mainly due to the filamentous network and their possible interactions with macromolecules of the cardiac jelly matrix. It is suggested that the factors that control the depositon of the connective tissue macromolecules and the assembly of the filamentous network are significant factors which influence the morphogenesis of the early embryonic heart.