[Role of calcium ions in the processes of modulation of serotonin responses of Helix pomatia neurons to the application of serotonin].

Role of calcium ions in modulating action of serotonin on acetylcholine (ACh) responses in nonidentified and identified (LPa3, RPa3) neurons of Helix pomatia was studied using the voltage-clamp method. An exposure for 1 min to serotonin before ACh application decreased the ACh response in the LPa3 neuron and increased it in the RPa3 neuron. Extracellular administration of theophylline and dibutyryl-cAMP produced analogous effects in these neurons. The injection of calcium ions into LPa3 neuron increased the ACh-induced current in the presence of serotonin, i.e. changed the type of the modulating action of serotonin on the ACh response in this neuron. The injection of calcium ions into the RPa3 neuron enhanced modulating action of serotonin on the ACh response without any change in a type of modulation, while EDTA injection elicited opposite effects. The increase of extracellular calcium concentration inhibited modulating action of serotonin on acetylcholine responses in RPa3 neuron. The regulatory role of calcium ions in the modulating action of serotonin on acetylcholine responses in tested neurons and participation of cAMP are discussed.