[Ionic mechanisms of the modulating effect of serotonin on acetylcholine responses of neurons in the edible snail].

Ionic mechanisms of modulating action of serotonin on acetylcholine responses in identified and nonidentified neurons of Helix pomatia were studied using the voltage-clamp method. A 1-3 min exposure to serotonin (10(-5)-10(-4) mol/l) depressed DNa-type, DCl-type and HCl-type of responses to acetylcholine (10(-6)-10(-4) mol/l) without modification of the reversal potential of acetylcholine-induced current. Theophylline produced effects analogous to those of serotonin which evidences for the participation of intracellular processes connected with the cyclase system of cell in modulating the serotonin action on acetylcholine responses. Serotonin produced a shift of the reversal potential and an increase of acetylcholine-induced current in neurons whose acetylcholine responses were associated with changes in the membrane permeability for several kinds of ions. Serotonin inhibited the inward current phase when two-phase acetylcholine responses of DNa-HK-type were observed. Ionic mechanisms of the modulating action of serotonin on acetylcholine responses in tested neurons are discussed on the basis of the data obtained.