Effects of saponin on contractile force and intracellular ion activities of cardiac tissues.

The effects of the glycoside saponin on ferret ventricular muscle have been investigated. Saponin produced a positive inotropic effect, the extent of which was determined by the bathing calcium concentration. If the bathing calcium concentration is reduced to levels equivalent to those found intracellularly then similar saponin concentrations are able to "skin" the cardiac cells. The effects were further investigated in sheep heart Purkinje fibres. In the presence of normal extracellular calcium concentrations (to prevent skinning), saponin produced increases in sodium activity, decreases in potassium activity but little change in intracellular pH. The decreases of potassium activity were compared to the effects of strophanthidin. The changes in intracellular ion levels were accompanied by the development of a contracture. The effects of saponin could be explained by its interaction with cholesterol in the cell membrane resulting in an increase in membrane permeability to sodium which may be part of a nonspecific increase in membrane permeability.