Factors Involved in the Loss of Spontaneous Contractile and Electrical Activity in Clusters of Cultured Cardiac Cells

Abstract

Beating cell clusters were obtained by trypsinization from hearts of newborn rats. Spontaneous activity ceased after several weeks while the cultures were still proliferating. Experiments were performed to identify the physiological determinant causing cessation of spontaneous activity. (a) Cell clusters having lost their spontaneous activity responded to extracellular stimulation. (b) Reduction of [K]o by 50% increased the number of beating cell clusters by 40%; doubling [K]o reduced the number of beating cell clusters by 49%. (c) Cell clusters which were in the process of losing their ability to contract spontaneously needed a progressively increasing temperature to induce spontaneous activity. These results suggest (1) that the pacemaker mechanism fails first when a cell cluster loses its spontaneous activity and (2) that shortly before the cluster fails to contract spontaneously, it requires more energy to maintain pacemaker activity because of possible structural membrane changes or changes in the enzyme pattern of the cells.