Specificity of the Effects of Cardiac Glycosides on the Rhythmic Contraction of Single Cultured Cardiac Muscle Cells

Abstract

FROM fragments of embryonic chick hearts treated with trypsin, single, rhythmically contracting cells can be grown in a fluid, semisynthetic culture medium¹. Exposure of these cells to cardiac glycosides in concentrations as low as 10⁻⁹–10⁻⁸ M results in an increase in the rate of beat². In addition the pulsations appear to become stronger. At concentrations of 10⁻⁷ M and above, the acceleration of pulsation is soon followed, or is accompanied, by disturbances of automaticity and of co-ordinated contractile activity. By means of phase-contrast, high-speed microcinematography of cells anchored to the glass surface these effects could be studied in greater detail³. The motion pictures revealed changes at the cellular level which strikingly resembled some of the familiar manifestations of digitalis poisoning in the heart of animals and of man. Such phenomena as partial and complete block of propagation of the contraction wave (presumably due to block of conduction), bigeminal rhythm, ectopic beats, tachycardia, and fibrillation could all be observed in single isolated ventricle cells.