EFFECTS OF DISULFIDE BOND REDUCTION ON THE EXCITATORY AND INHIBITORY POSTSYNAPTIC RESPONSES OF APLYSIA GANGLION CELLS

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Abstract
Three kinds of the cholinoceptive neurons, nicotinic depolarizing (D)-, nicotinic hyperpolarizing (H)-, and muscarinic H-types, as well as two other kinds of neurons, GABA H-and dopamine H-types, were identified in Aplysia abdominal ganglion, and the effects of disulfide bond reduction and reoxidation on their postsynaptic responses were studied by measuring conductance change produced by each transmitter. The acetylcholine-induced responses of both nicotinic types (D-and H-) were depressed by reducing the disulfide bonds witn aitniotnreitol (DTT) and restored by reoxidizing with 5, 5'-dithiobis-(2-nitrobenzoic acid):(DTNB), whereas the responses of the muscarinic H-, GABA H-, and dopamine H-cells were not affected at all by either DTT or DTNB. In contrast to the results obtained from the electroplax, the cholinergic receptors in our preparation showed neither the activation by hexamethonium nor the augmentation of decamethonium-induced responses after reduction of disulfide bonds.In addition, our preparation did not demonstrate the long-lasting responses to bromoacetylcholine, which was often observed in the electroplax after reduction of S-S bonds. DTT-induced depression of the nicotinic responses was studied on the dose-response curves; the mode of receptor inhibition was rather comnlexed. being neither tvae of competitive nor non-competitive. We concluded that the disulfide bond is a crucial element in both types of nicotinic receptors (D and H), and that this bond is related to the activation process of the receptors regardless of their ionic specificities.