In a previous work ~' we analysed the differences and similarities in the response to preganglionic stimulation and to the injections of acetylcholine of the superior cervical ganglion of the cat. These experiments led us to the conlusion, that the acetyleholine released from the preganglionie endings and that diffusing from the blood vessels to the ganglion cells act on different sites: the two sites of action are represented by two distinct systems of acetyleholine receptors. While the acetyleholine liberated from preganglionie endings acts first of all on the so-called innervated receptors, located in the innervated membrane areas of the ganglion cell, the acetylcholine diffusing there from the blood stream combines with the so-called free receptors in the areas not covered by preganglionic endings. According to our experiments, the system of innervated receptors is less sensitive to acetylcholine, can be selectively blocked with penta-and deeamethonium, while the system of free receptors is more sensitive to aeetyleholine and can be paralysed with atropine and choline derivatives. We have proved in our experiments that the differences are based not on permeabiBty features, but on differences in the structure of the aeetyleholine receptors.
In ~he next phase, we have undertaken to study the kinetics and energeties of the combination of acetylcholine whith these receptor systems and to draw conclusions as to the structure of the postsynaptie membrane of sympathetic ganglion cells.
Methods
The superior cervicM ganglion of cats, i.p. narcotised with 80 mg/kg of chloralose, was perfused with Locke's solutior~ containing 10 -6 3/[ TEPP, by the method of K_r~:rAxov 6. Through a suitable side branch of the perfusion eannula injections and infusions could be administered into the blood ~ressels supplying the ganglion. Preganglionic stimulation was effected by means of a square wave generator, at 5 V and 2 msee, 10 c/see, for 5 sec. The contractions of the nictitating membrane were recorded by means of a~ isotonic lever. In the course of the experiments