[Development of the intercalated disc in culture]

A culture of separated chick embryo heart cells was observed for 48 hours. By electron microscopy it was observed that at the sites of contacts made during culture intercalated discs did not in general develop. Previous reports to the contrary are devoid of controls excluding the possibility that the intercalated discs found originated from the tissue with which the culture was started. Their electron micrographs, in any case, related to the mature state of the tissue used. In one part of the culture used here the site of a contact which had developed in culture shows a fascia adherens to which filaments (of up to myofilament diameter) insert on both sides. Their course, however, is irregular in one cell, and in the other they are very sparse. Z-lines are missing and only round Z-bodies are to be seen, so one can only speak of an intercalated disc at the earliest stage of development. These findings agree with the recently published statement of Gross and Müller (1977), according to which intercalated discs did not develop even during common pulsation of heart muscle cells for two and a half month, provided that during culture a certain mechanical momentum did not supervene. It is supposed that the intercalated disc Anlage here demonstrated represents one of the most advanced states to which spontaneous development, without mechanical momentum, can lead .