Tunicate heart as a possible model for the vertebrate heart

A number of problems in cardiac physiology are related to the structural complexity of the tissue. For instance, the tortuous and partially confined extracellular space represents a slowly exchangable compartment in which ions or metabolites may accumulate or deplete during activity. Other problems emanate from the inhomogeneous distribution of intracellular potential and the branching nature of the myocardial cells. Our results suggest that the sea potato heart may be functionally treated as a single layer of myofilaments adjacent to a single active membrane which controls excitability and E-C coupling processes. Yet in many ways this simple structure functions similarly to the vertebrate heart when comparing the action potential, the calcium requirement, and the mechanics of muscular contraction. It is concluded, therefore, that the sea potato heart serves as a good model of the vertebrate heart for investigation of the fundamental properties of cardiac muscle. In fact, this preparation may make it possible to examine the details of the molecular mechanisms of ionic transport and mechanics of muscle contraction, thereby supplementing the results that have been or are being obtained from the mammalian myocardium.