Stretch-induced excitation and conduction disturbances in the isolated rat myocardium*

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Summary

The transmembrane potentials and isometric force were simultaneously recorded from the isolated myocardia of the rat, rabbit, cat, guinea pig and frog. The rat papillary muscle, in contrast to preparations from the other species, was uniquely sensitive to transient stretch. Stretching the rat papillary muscle to lengths 5 to 10% greater than L0 (the muscle length producting maximal peak isometric force) caused the rat preparations to behave in a graded and asynchronous manner. Simultaneous recordings of the electrical and mechanical activity of the transiently stretched rat papillary muscle demonstrate phenomena such as delayed activation, decremental conduction, subthreshold electrotonic potentials, stimulus-dependent graded contractile behavior, and electrical and mechanical alternation. All of these phenomena were reversible with time and could be explained in terms of partial conduction block induced by stretch.

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*

This work was supported in part by grantsfrom the American Heart Association, 68-737, and a United States Public Health Service Predoctoral Traineeship.

Taken in part from a dissertation submittedto the graduate School of Arts and Sciences, University of Pennsylvania, 1969, in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Dr. Spear is presently a post-doctoral fellow of the Southeastern Pennsylvania Heart Association.

1

From the Department of Physiology, Universityof Pennsylvania School of Medicine, and the Comparative Cardiovascular Studies Unit, The School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.

Dr. Moore is the William Stroud EstablishedInvestigator of the American Heart Association.

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