Requirements for spontaneous contractility in isolated adult mammalian heart muscle cells

Abstract

Spontaneous contraction and relaxation of adult mammalian heart muscle cells can be observed immediately after separation of such cells from myocardium by mechanical mincing. This spontaneous contractility requires added ATP and magnesium, but is not dependent on a specific monovalent cation. Under conditions which minimize the possibility of ATP synthesis, UTP, CTP, ITP or dATP could support spontaneous beating. The period of time during which an ice-cold cell suspension will continue to provide beating cells (homogenate survival time, HST) was used as the major assay for the effects of different medium components. Increment of sucrose, bringing the medium tonicity up to almost 500 mOsm/kg produced a prolongation of HST. A mixture of vitamins and amino acids prolonged survival to a greater extent than could be accounted for by a tonicity effect. Calcium at all concentrations tested reduced the HST, as did manganese. Separated cells continued to beat spontaneously for over 4 h when kept in a flowing stream of fresh medium at room temperature. The absence of specific monovalent cation requirements and the calcium contracture response indicate major differences between the isolated cells and intact myocardium. Whether these differences reflect damage to the isolated cells incurred during preparation or are intrinsic properties of separated adult heart cells is not clear.