ELECTRICAL-ACTIVITY OF THE CRAYFISH MYOCARDIUM

Introduction: The purpose of this investigation was to study the electrical activity of the crayfish myocardium. Methods and Results: In isolated crayfish hearts, intracellularly injected hyperpolarizing pulses propagate electrotonically to distances up to 1 mm, and the myocardium behaves as an irregular functional syncytium. Conclusion: The existence of low-resistance intercellular connections provides a basis for the analysis and interpretation of many of the results obtained in this article, and makes it possible to propose the following tentative conclusions: (1) in the crayfish myocardium, not all muscle cells are innervated, yet many sites in the crayfish myocardium receive the same polyneural innervation; (2) in many records, the burst of junction potentials that follow each action potential are electrotonic in nature; (3) the cardiac muscle fibers of the crayfish heart are electrically excitable, and the generated action potentials do propagate actively at least for short distances; (4) the gaps between the innervated sites are filled with noninnervated but connected muscle cells that are passively and actively engaged; and (5) an exaggerated richness of innervation is not needed since the crayfish heart can provide effective and quasisynchronous mechanical systoles because of its efficiently combined characteristics.