Acetylcholinesterase in the Conductive Tissue of the Heart

It is shown that the Purkinje system of bovine hearts contains a specific acetylcholinesterase resem-bling that of nervous tissue, in an amount comparable-to that of-peripheral nerve. Its possible implication in the conduction of impulses in the heart is discussed. THE CONDUCTIVE system in themammalian heart is a specialized partof the myocardium, distinguished by its ability to conduct stimuli at the relatively high rate of 4 meters per second, some 10 times the rate of propagation in the unspecific cardiac musculature.8 ' '8 Since in nervous tissue the conduction of the impulse is correlated with the breakdown and resynthesis of acetylcholine,21- "•24 '25 we raise the question whether in the differentiation of the Purkinje tissue also the cholinergic sys-tem has come into prominence. In this study, we have examined the action of the acetylcho-line splitting enzyme, postponing the investiga-tion of the synthesis of acetylcholine, and other aspects of the problem, to future work. Two main types of choline esterases have been distinguished. With regard to its substrate specificity, the acetylcholinesterase of nervous tissue differs markedly from the nonspecific cholinesterase of some other sources.15 ' 29 Sev-eral authors found that the enzyme of the myo-cardium is predominantly of the unspecific type, different from that of nerve2 ' 13 ' 26 ' 27; it was the aim of the present work to characterize the enzyme from the conductive tissue