Protoplasmic Movement in Cardiac Muscle During Interval Between Contractions

Abstract

The question of whether muscular contraction is related to the more general type of protoplasmic motion exhibited by nearly all cells is brought forward and partially answered by the following observations of both types of motion in the same cells.

The material consisted of tissue cultures of cardiac muscle whose spontaneous rhythmic contractions were interrupted by periods of rest. The explants were taken from the hearts of 16-day-old rat embryos and cultivated in a medium of rat plasma and embryo extract. 1 Most of the observations were with cultures incubated for 4 or 5 days without subculturing. The spontaneous contraction of heart muscle in tissue cultures is subject to variation both in the rapidity of its rate and the regularity of its rhythm. One of the irregularities is a remittent form in which short periods of rhythmic contraction alternate with similar or longer periods of rest. These cultures with remittent activity provided material in which cells of known contractile power could be studied during periods of quiescence.

The strands of new muscle growth which were to be observed for the slow unspecialized protoplasmic motion were first watched through the microscope to make sure that all the muscular elements contracted vigorously during the period of rhythmic activity. They were then focused on the film of a 16 mm movie camera through the 1.5 mm, 120× objective of the microscope. In order that the slow protoplasmic motion might be appreciated by the eye, it was made more rapid on the film by increasing the time between exposures. The exposures were taken every 5 seconds. Projected at the rate of 16 frames per second, the finished film increased the rapidity of motion 80 times.