THE CYTODIFFERENTIATION OF MYOCARDIAL CELLS FROM 4-DAY EMBRYONIC CHICK HEARTS GROWN IN CULTURE

Abstract

A study has been made of the growth, behavior, and differentiation of myocardial cells from ventricles of the 4-day chick embryonic heart growing in vitro. The trypsinized heart cells were cultured on Maximow slides in a medium of cockerel plasma and chick embryo extract. All 500 cultures were examined with the phase contrast and the polarizing microscopes and permanent records were made using time-lapse cinematography. Differentiation of myofibrils, best followed with the polarizing microscope, was initiated by the appearance of birefringent thickenings, localized along the fibril. These bands increased rapidly in number, forming sarcomeres. A myofibril began to contract when a few sarcomeres were present. Non-striated myofibrils within the same cell did not pulsate. Completely striated myofibrils, in juxtaposition, fused with their sarcomeres in perfect alignment. When myocardial cells were slightly retracted, the myofibrils became folded as they relaxed and the folds always occurred at the Z bands. As myocardial cells degenerated, the mitochondria became vesiculated and the nucleus became pyknotic, but the striated configuration along the myofibrils could still be distinguished. From these observations of cultured myocardial cells, we believe that myocardial cells do not contract until bands have differentiated along the myofibrils.