PROPERTIES OF A DELAYED RECTIFIER POTASSIUM CURRENT IN DENTATE GRANULE CELLS ISOLATED FROM THE HIPPOCAMPUS OF PATIENTS WITH CHRONIC TEMPORAL-LOBE EPILEPSY

Purpose: Properties of potassium outward currents were investigated in human hippocampal dentate gyrus granule cells from 11 hippocampal spe cimens obtained from patients with temporal lobe epilepsy (TLE) during resective surgery. Methods: Dentate granule cells were isolated enzym atically and outward currents analyzed by using the whole cell configu ration of the patch-clamp method. Hippocampal specimens were classifie d neuropathologically with respect to severe segmental cell loss, glio sis, and axonal sprouting (Ammon's horn sclerosis, AHS), or the presen ce of a focal lesion in the adjacent temporal lobe. Results: A delayed rectifier outward current (I-K), but not an A-type potassium current (I-A) or inwardly rectifying potassium currents, was observed in all c ells. The average current density of I-K, the time-dependent decay of I-K, and the resting membrane characteristics were not significantly d ifferent between patients with and without AHS. The voltage of half-ma ximal activation V-1/2(act) was 5.4 +/- 1.8 mV in AHS compared with -2 .9 +/- 1.8 mV in lesion-associated epilepsy (NS). In contrast, V-1/2(i nact) 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 m V; p = 0.0017). Conclusions: The altered steady-state voltage-dependen ce of I-K may result in abnormal excitability of dentate granule cells in AHS and exert a marked influence on input-output properties of the dentate gyrus.