Genesis of MEG signals:: II.: Effects of manipulating voltage- and Ca2+-activated K+ channels on the magnetic fields produced by the CA3 slice of guinea pig

Background. There are several types of K+ channels in the hippocampal neurons which play important roles in determining the resting membrane potential, repolarizing action potentials and controlling periods of neuronal firing. In this study, effects of manipulating voltage- and Ca2+- activated K+ currents were investigated to understand the contribution of these ionic conductances in generating evoked magnetic fields (EFs). Methods. The EFs were measured simultaneously with extracellular field potentials (V-ex) in one set of experiments using a longitudinal CA3 slice preparation and V-ex and intracellular potentials (V-in) in another in presence of different channel blockers of K+-channels. Results. The stimulation of the pyramidal cell layer produced a biphasic EF, whereas the stimulation of the apical dendrites produced a triphasic EE Bath application of various blockers of K+-conductances showed profound effects on late components of the EF. Conclusions. K+ conductances play an important role in determining shape and size of the magnetic field produced by the hippocampal slice.