DIFFERENTIATION OF HEART CELLS IN A CHEMICALLY DEFINED MEDIUM

Single cells were isolated with the aid of trypsin from fragments of ventricles and atria of embryonic chicks of 11 days of incubation and were cultivated in vitro. By the use of new techniques the autorhythmicity of the heart cells can be maintained under standardized conditions of cultivation in the chemically defined medium SM 20, containing 1.3 mM K+, for more than 30 days and in the SM 20 containing 5.1 mM K+, for only 4 to 11 days. During the first half of the cultivation period in the SM 20 containing 1.3 mM K+ there is a significant difference between the rate of pulsation of the atrial cells and the ventricle cells. In the course of cultivation the rate of pulsation of the atrial cells changes in a manner similar to that of the heart during ontogenesis. After the first or the second day the rate of pulsation in the 1.3 mM K+-containing SM 20 is significantly higher than the rate in the SM 20 containing 5.1 mM K+. In the heart cells cultivated in the SM 20 for 16 to 20 days typical myofibrils are formed with Z, I and A bands. Neither extracellular fatty acids and lipids nor serum proteins are required by the cell layers for the maintenance of automaticity, for functional differentiation, and for myogenesis. Adaptation of the cells or cultivation in conditioned media is likewise unnecessary for differentiation. Problems of function and structure in connection with the extracellular environment in vitro are discussed. The maintenance of organ-specific characteristics in a synthetic medium opens new possibilities for a quantitative muscle cell culture. © 1968 Springer-Verlag.