Temporal lobe epilepsy and changes in the M current

Objective: Acquired alterations of ion channel function occur after status epilepticus (SE).Kv7 channels mediate a sustained outward current (IM) that exerts pivotal control over neuronal excitability.Here, we investigate if pilocarpine-induced SE alters M-channel activity by quantifying the IM.Methods: Hippocampal slices were prepared from adult rats after pilocarpine-induced SE, when the animal was showing 3-5 spontaneous recurrent seizures (SRS) a day.A group of untreated, age-matched rats was used as the control group.Recordings were made using the whole-cell configuration of the patch clamp technique and current clamp mode to measure the membrane time constant.Results: The IM measured amplitude in CA1 neurons from pilocarpine-SE rats was significantly reduced compared to the control group (control, 208.72 25.49 pA, n = 15; pilocarpine-SE, 49.28 6.17 pA, n = 11; p < 0.05, Student's t).The time constant was 27.7 17.7 msec in the control group and 48.9 5.5 msec in the pilocarpine-SE group, and was significantly different (p < 0.05).Conclusions: In this study, we demonstrated that the M-current amplitude is significantly reduced in CA1 pyramidal neurons after pilocarpine-SE.Considering the acute damage that SE induces, the silent interval between injury and the onset of spontaneous seizures, and the chronic epileptic state in which the M-current was measured, we can speculate about the lack of homeostatic regulation of the intrinsic properties of neuronal excitability.