Abstracts

Rationale: Voltage-gated, M-type potassium channels, composed of KCNQ2-5 subunits, play a dominant role in neuronal excitability and are widely expressed throughout the brain. Consequently, M channels have become a promising target in epilepsy treatments and M-channel openers are novel anti-epileptic drugs. Recently, we showed that KCNQ2 and KCNQ3 mRNA to be profoundly upregulated in the hippocampus following a chemoconvulsant seizure, dependent on A kinase-anchoring protein (AKAP)150. Thus, we propose that AKAP150-dependent M-channel upregulation is a homeostatic, anti-epileptogenic mechanism in response to seizures. However, it remains unknown how this upregulation affects the voltage dependence and amplitude of M currents in the hippocampus, the frequent locus of medial temporal lobe epilepsy. Here, we test the hypothesis that M-current amplitudes in the hippocampal formation are increased following a pilocarpine-induced episode of status epilepticus. Methods: M currents were recorded under perforated-patch and whole-cell voltage clamp from dentate gyrus (DG) granule cells and CA1 pyramidal cells in mouse brain slices. Both types of neurons were identified by signature characteristics under current clamp, based on input resistance and spiking responses to depolarizing current injections. Seizures will be induced in mice using repeated subthreshold doses of pilocarpine (100 mg/kg, i.p.) administered every 20 minutes until achievement of status epilepticus (SE). The functional properties of M currents will be compared between sham and SE-experienced mice. Results: The vast majority of granule cells and CA1 pyramidal neurons displayed characteristic M currents, determined by the classic M-current voltage protocol, in which the cell is held at -20 mV, and the deactivating relaxation is quantified during a 700 ms hyperpolarizing step to -60 mV. The voltage dependence of activation was measured by quantifying the amplitude of the "tail current" at -60 mV after a family of 1 sec steps from -60 mV to 0 mV. In both types of cells, bath-application of the M-channel opener, retigabine (RTG, 10 uM), increased the holding current at -20 mV, augmented the amplitude of the relaxation at -60 mV, and shifted the voltage dependence to more hyperpolarized values, consistent with the known properties of retigabine as an M-channel opener. Conclusions: Our data shows that M-type potassium channels are functionally expressed in both DG granule cells and CA1 pyramidal cells. We will report the effects of chemoconvulsant seizures on the voltage dependence and amplitude of M currents in both types of hippocampal neurons in mouse brain slices.