“Slow-Motion” Cinematographs of the Contraction of Single Cardiac Muscle Cells

Abstract

The material for this study was supplied by tissue cultures of embryonic heart in which the cardiac muscle had grown out and become differentiated. The ventricles of 16 day rat embryos were cut into fragments 1 to 2 mm. in diameter and cultivated in a medium composed of rat plasma and embryo juice. In the course of 2 to 4 weeks a new growth of muscle appeared among the fibroblasts, taking the form of anastomosing bands similar to adult cardiac muscle. This new growth was closely applied to the under surface of the cover glass so that single cells could be observed with the highest powers of the microscope. Cross striations could be seen in many of the muscle cells of both explant and new growth after one month. The striated appearance in the living cell was produced by the arrangement of small brick-shaped bodies, apparently mitochondrial in nature, into more or less regular longitudinal and transverse rows. Since this picture was somewhat different from that presented by muscle from an adult animal it seems likely that we were dealing with a transition stage in which the differentiation was incomplete. The presence of myofibrillae with alternating dark and light bands and “membranes of Krause” in fixed preparations, however, indicated that the process was well advanced. Although the muscle in these cultures contracted spontaneously, its activity was intermittent, especially when exposed to room temperature for the making of photographs. This irregularity was overcome by substituting Ringer solution for the usual medium.

Since the intracellular movements were too rapid to be followed by direct observation through the microscope, an effect of slowing was accomplished by making “slow-motion” cinematographs. Exposures were taken at the rate of 32, 48 and 64 per second.