EFFECTS OF INNERVATION AND DRUGS UPON DIRECT MEMBRANE POTENTIALS OF EMBRYONIC CHICK MYOCARDIUM

¹ Departments of Pharmacology, Physiology and Medicine, University of Utah College of Medicine, Salt Lake City, Utah

Direct membrane potentials of embryonic chick atrium and ventricle have been characterized. Membrane potentials of the atrium and the ventricle of both non-innervated and innervated hearts are qualitatively identical and similar to those of the adult frog ventricle. Quantitative differences between membrane potentials of chick hearts of different ages are of minor magnitude and do not indicate that they result from the establishment of innervation.

Acetylcholine, epinephrine and digitoxin modify membrane potentials characteristically, the pattern of alteration by each drug being the same in both the atrium and the ventricle and in both the non-innervated and the innervated heart. No marked increase in sensitivity of the innervated myocardium to epinephrine and acetyicholine was observed.

These observations support the concept that the non-innervated myocardium possesses marked maturity and do not support the generally accepted concept that establishment of innervation endows the embryonic heart with marked increased sensitivity to chemical mediators.