Embryonic myocardial cell aggregates: volume and pulsation rate.

Abstract Spontaneously beating aggregates of myocardial cells from whole heart, atria, and apical portions of the ventricles were prepared by trypsin-dissociation and gyratory reaggregation of 4-, 7-, and 14-day-old chick embryo tissue. Pulsation rate and volume of aggregates were determined. The pulsation rate for a given volume aggregate decreased as the age of the donor embryo increased. Atrial aggregates of a given size beat faster than ventricular aggregates of the same size. However, in all cases the pulsation rate varied inversely with the aggregate volume. These results are not in agreement with the pacemaker concept as generally accepted, which predicts that a mass of heart cells would take on the pulsation rate of the fastest cell or cells within it. Differential composition of large and small aggregates was ruled out as a determining factor in the inverse rate-volume relationship. We suggest that (a) limited diffusion in large aggregates compared to small aggregates or (b) the larger total membrane capacitance of the electrically coupled cells of larger aggregates compared with that of smaller aggregates, plays a major role in setting the pulsation rate.

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