Resumo

Objectives: Studies show that epileptiform activities can be generated and sustained without the actuation of chemical synapses. In the present work we aimed to determine the contribution of non-synaptic mechanism in normal levels of Ca2+, during epileptiform activities ictal and interictal. Materials and methods: As experimental model, we used hippocampal slices from Wistar rats aged 4-6 weeks. The induction of epileptiform activity in CA1 region were made using high [K+]0 protocol, with and without the addition of Ca2 and recorded by eletrophysiological and optic methods. Computer simulations were performed in order to interpret the experimental results, which was done by analyzing the parameters responsible for the behavior of these events and the dynamics between the synaptic and non-synaptic connections. The data were analyzed by statistical comparisons (ANOVA) (n = 22, p <0.05). Results: The analysis of the extracellular potential parameters disclosed a morphological similarity between ictal epileptiform events with and without the addition of Ca2+= (DC component = 6.30 ± 0.09 mV and 6.31 ± 0.24 mV; duration event = 11:33 ± 0.15 s and 14.83 ± 0.27 s, respectively). The signal intrinsic optical showed the same increase in transmittance of light (with the addition of Ca2+= 1.18 ± 0.05 mm and without the addition of Ca2+= = 1:31 ± 0.07mm), suggesting the same level of neuronal recruitment. Computational modeling permitted to predict changes in the concentration of Na+, K+ e Cl- along the interictal and ictal events. These changes in ionic concentrations reflected alterations in the Nernst potential for each ion, influencing significantly the membrane potential. During the interictal events, the Nernst potential of ionic species had less alteration compared to transmembrane potential of ictal events. Conclusion : The interpretation of experimental results in addition to computer simulations allowed us to propose the same biophysical mechanisms for non-synaptic and synaptic ictal activities. Both are marked by two critical points: the first related to the beginning of event, when the influx of Na+ by ion channels overcomes its efflux by the Na / K pump, the second, related to the ending of event, when the Na efflux by pump becomes greater than its influx through the ion channels. These data reinforce that the mechanisms involved in ictal events during the synaptic epileptiform activities have non-synaptic nature and interictal events are synaptic nature. Financial support: CAPES