ELECTRON MICROSCOPIC HISTOCHEMISTRY OF CHOLINESTERASE ACTIVITY IN THE BARORECEPTOR OF THE CAT ATRIAL ENDOCARDIUM

概要

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The fine structural localization of the cholinesterase (ChE) activity was studied in the presumed baroreceptors of the cat atrial endocardium. The unit of baroreceptors belonging to one myelinated fiber was about 60×10μm, in which the axon terminals were delicately arborized and intermingled with collagen fibrils. Such axon terminals were identified by forming varioussized varicosities ranging from 1 to 3 μm in diameter, containing numerous mitochondria and a few dense bodies. A large portion of the axolemma of the varicosities was covered only by basement membranes, being in direct contact with the connective tissue. Such ultrastructural characteristics were closely similar to those of the baroreceptors in the carotid sinus, aortic arch and endocardium, as reported by other investigators. The enzyme activity was found mainly in the spaces between the axon terminals and the surrounding Schwann cells. The nuclear envelope in some Schwann cells also displayed reaction products. No definite enzyme activity was demonstrated in any of the organelles in the axon terminals. It is assumed that ChE in the baroreceptors might be synthesized and released by the Schwann cells which surround the axon terminals. The specific localization of ChE activity in the baroreceptors suggests that, similar to other mechanoreceptors, ChE has some important functions in the baroreceptors.
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