Isometric dynamic response of mammalian heart muscle due to step changes in the calcium concentration of the perfusing medium.

The isometric tension transient response of isolated kitten papillary muscle was found to exhibit direction-dependent dynamics when subjected to step changes in the calcium concentration of the bathing medium. The tension transient curves could be resolved into a minimum of two to three exponential components, which could be considered to indicate different calcium compounds or compartments within the muscle. However, a model relating calcium diffusion across the muscle to the dose-response curve indicates that the exponential components of the tension transient curves are due to the properties of calcium diffusion through the extracellular space, and that the direction-dependent dynamics are caused by the nonlinearity of the dose-response curve.