Differences in frog skeletal and cardiac muscle exitation

Abstract

Introduction: The problem of muscle excitation is an important component of research in experimental physiology as well as in clinical sciences such as cardiology and sports medicine. When trying to determine intercellular interactions of the excitation transmission, there were restrictions of methodical nature. We propose a new methodological approach to assess the distribution of action potentials in skeletal and cardiac muscles of frogs. Methods and Results: For action potentials recording we used polytrode (multichannel conical microelectrode), sharpened as a pencil. With this treatment the contact areas are located in one zone close to each other at a fixed distance. The polytrode was placed into the intercellular space of gastrocnemius muscle of a frog and potentials of several adjacent muscle fibers were recorded. We recorded spreading of excitation in the gastrocnemius muscles during tetanic contraction and during the rest period. It was found that tetanus is accompanied by the rhythmic action potentials that were recorded by all channels of the polytrode. During the rest time a tonic contraction takes place, when single action potentials are observed, enveloping only individual muscle fibers without being distributed to the neighboring fibers. Such contractions were recorded as a series of potentials at individual contact sites of the polytrode. After recording the action potentials of skeletal muscle we have placed the polytrode into the cardiac muscle tissue. The peculiarity of the heart is a solitary contraction when short potential covers sequentially all fibers and it was recorded on the all the channels simultaneously as one solid “wave”. Conclusion: Our research shows that the excitation of skeletal muscle demonstrated individual potentials from individual muscle fibers. It looks very similar to a myogram of skeletal muscle during the titanic contraction. In the cardiac muscle due to the peculiarities of its structure and ability to transfer the action potential from one cardiomyocyte to another the oscillogram looks like summation of excitations of individual fibers with a very small interval.