Role of calcium ions in processes of serotonin-induced modulation of neuronal response to acetylcholone application in Helix pomatia

Abstract

The role of calcium ions in modulating serotonin action on acetylcholine (ACh) response in nonidentified and identified (LPa3 and RPa3) neurons ofHelixpomatia was investigated using voltage-clamping at the neuronal membrane. Exposure for 1 min to serotonin prior to ACh application reduced response to ACh in neuron LPa3 and raised it in RPa3. The same two patterns of modulating ACh-induced response were produced by extracellular application of theophylline and dibutyryl c-AMP. Injecting calcium ions into neuron LPa3 led to reinforcement of ACh-induced current in the presence of serotonin, thus changing the pattern of serotonin-induced modulation of ACh response in this unit. In neuron RPa3, the same process enhanced the serotonin-induced modulating effect on ACh response but without changing the pattern of modulation, while injected EDTA produced the reverse effects. Increased intracellular concentration of calcium ions brought about a reduction in the degree of serotonin-induced modulation of ACh response in neuron RPa3. Possible reasons are discussed for changes in serotonin-induced bimodal modulation of ACh response in test neurons produced by altering the extracellular concentration of calcium ions.