The augmentation of postsynaptic potentials in crustacean muscle fibers by cesium. A presynaptic mechanism

Abstract

1. 1. Substitution of Cs for K in Homarus saline markedly augments both excitatory and inhibitory postsynaptic potentials of lobster muscle fibers. 2. 2. This augmentation of the postsynaptic potentials (p.s.p.'s) by Cs requires an induction period of 2 hr and the absence of external K. Presence of K or low Ca concentrations abolish the Cs effect. After the Cs-induced augmentation of the p.s.p.'s reaches its maximum, removal of the Cs from the saline produces little change from the augmented values. 3. 3. The Cs effect is found in a number of neuromuscular junctions of lobster, and also in other crustacea. 4. 4. The Cs effect is not due to changes in the following properties of the postsynaptic cell: membrane potential, membrane resistance, reversal potential of the p.s.p.'s, or sensitivity of the membrane of the postsynaptic components to the synapse activator agents. 5. 5. Thus, Cs appears to act on the terminals of both excitatory and inhibitory axons, so that a single stimulus will evoke the release of greater amounts of transmitter than under normal conditions.