PRE‐ AND POSTSYNAPTIC UTILIZATION OF ATP AND CREATINE PHOSPHATE AT THE NERVE‐ELECTROPLAQUE JUNCTION

IRrcri~~vrl 29 hltr!. 1973. .4c~rptrd 25 Julv 1973) Abstract-When the electric organ of the Torpedo fish was stimulated in riro and in vitro. there was a large rapid breakdown of creatine phosphate (CrP). and a slower decrease in the level of ATP. The acetylcholine content showed a parallel fall to that of ATP. Curare was used to interrupt synaptic transmission, allowing the presynaptic nerve endings to remain sensitive to stimulation, but simultaneously keeping electroplaques inactive. In stimulated curarized tissue, the level of ATP was not changed, while the breakdown of CrP was still 29; of that observed in non-curarized controls. These observations suggest that presynaptic nerve endings. despite their small size, utilize a very high amount of energy. THE ELECTRIC organ of Torpedo is made of stacks of electroplaques which are homologues of muscle cells and are covered by a great number of cholinergic nerve terminals. In this organ and the one of Elrcrrophorus, stimulation of the nerves has been found to decrease the total amount of ATP and CrP (KISCH, 1930; NACHMANSOHN et a/., 1946; CHENG & KEYNES, 1967). The energy used in this tissue is presumably required for the restoration of the ionic gradients in the electro- plaques and the nerves, and for the synthesis, accumula- tion, and release of the neural transmitter substance by the nerve endings. In order to study what proportions of energy are consumed by the electroplaques and the presynaptic nerve terminals respectively, the breakdown of ATP and CrP in the stimulated electric organ of Torpedo was measured before and after the application of curare. This drug is known to block the action of the trans- mitter on the postsynaptic membrane. It does not, to any great extent, interfere with the functions of the presynaptic nerve endings, as confirmed in the present experiments by the fall of the acetylcholine (ACh) content after stimulation (see Results). The organ of Torpedo was chosen. because its electroplaques are not excitable by an electric current. Consequently. curare abolishes the electrical discharge of the tissue, even when it is subjected to direct 'field' stimulation (AUGER & FESSARD. 1941). In other experiments done iri tico, the tissue was also stimulated through its nerves. and the net breakdown of ATP. CrP and ACh measured under these conditions, was compared to the values