Summary: Purpose: Properties of potassium outward currents were investigated in human hippocampal dentate gyrus granule cells from 11 hippocampal specimens obtained from patients with temporal lobe epilepsy (TLE) during resective surgery.
Methods: Dentate granule cells were isolated enzymatically and outward currents analyzed by using the whole-cell configuration of the patch-clamp method. Hippocampal specimens were classified neuropathologically with respect to severe segmental cell loss, gliosis, and axonal sprouting (Ammon's horn sclerosis, AHS), or the presence of a focal lesion in the adjacent temporal lobe.
Results: A delayed rectifier outward current (I), but not an A-type potassium current (Ik) or inwardly rectifying potassium currents, was observed in all cells. The average current density of Ik, the time-dependent decay of Ik, and the resting membrane characteristics were not significantly different between patients with and without AHS. The voltage of half-maximal activation V1/2(act) was 5·4 ± 1·8 mV in AHS compared with −2·9 ± 1·8 mV in lesion-associated epilepsy (NS). In contrast, V1/2(inact) was shifted in a hyperpolarizing direction in AHS (−67·7 ± 0·6 mV) compared with that in hippocampi not showing AHS (−47·7 ± 2·6 mV; p = 0·0017).
Conclusions: The altered steady-state voltage-dependence of Ik, may result in abnormal excitability of dentate granule cells in AHS and exert a marked influence on input-output properties of the dentate gyrus.