[Changes in intracellular calcium concentration during generation of high-amplitude EPSPs in grape snail neurons]

Change in intracellular calcium concentration is the main trigger of majority of physiological processes in the neuron including altering of gene expression and synaptic plasticity. We have found out that high amplitude EPSPs in command neurons of terrestrial snail similar to action potentials were accompanied by prominent calcium transients. It was shown that the amplitude of calcium transients accompanying high amplitude EPSPs in command neurons linearly depends on the strength of synaptic stimulation whereas dynamic of changes of EPSP amplitudes demonstrates pronounced saturation with increase of stimulus intensity. It means that in the certain range of membrane potentials calcium transients more accurately reflect stimulus strength then the level of membrane depolarization. We propose that calcium transients induced by high amplitude EPSPs are able to induce some biochemical changes in the neurons and therefore can mediate cell response at the subthreshold for action potential levels of membrane potential.