Molecular and functional changes in voltage-dependent na + channels following pilocarpine-induced status epilepticus in rat dentate granule cells

Abstract

Status epilepticus (S.E.) is known to lead to a large number of changes in the expression of voltage-dependent ion channels and neurotransmitter receptors. In the present study, we examined whether an episode of S.E. induced by pilocarpine in vivo alters functional properties and expression of voltage-gated Na + channels in dentate granule cells (DGCs) of the rat hippocampus. Using patch-clamp recordings in isolated DGCs, we show that the voltage-dependent inactivation curve is significantly shifted toward depolarizing potentials following S.E. (half-maximal inactivation at −43.2±0.6 mV) when compared with control rats (−48.2±0.8 mV, P<0.0001). The voltage-dependent activation curve is significantly shifted to more negative potentials following S.E., with half-maximal activation at −28.6±0.8 mV compared with −25.8±0.9 mV in control animals ( P<0.05). The changes in voltage dependence resulted in an augmented window current due to increased overlap between the activation and inactivation curve. In contrast to Na + channel voltage-dependence, S.E. caused no changes in the kinetics of fast or slow recovery from inactivation. The functional changes were accompanied by altered expression of Na + channel subunits measured by real-time reverse transcription–polymerase chain reaction in dentate gyrus microslices. We investigated expression of the pore-forming α subunits Na v1.1–Na v1.3 and Na v1.5–Na v1.6, in addition to the accessory subunits β 1 and β 2. The Na v1.2 and Na v1.6 subunit as well as the β 1 subunit were persistently down-regulated up to 30 days following S.E. The β 2 subunit was transiently down-regulated on the first and third day following S.E. These results indicate that differential changes in Na + channel subunit expression occur in concert with functional changes. Because coexpression of β subunits is known to robustly shift the voltage dependence of inactivation in a hyperpolarizing direction, we speculate that a down-regulation of β-subunit expression may contribute to the depolarizing shift in the inactivation curve following S.E.