Premium
Electrophysiological characterization of Na + currents in acutely isolated human hippocampal dentate granule cells
Author(s) -
Reckziegel G.,
Beck H.,
Schramm J.,
Elger C. E.,
Urban B. W.
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.139bo.x
Subject(s) - tetrodotoxin , time constant , chemistry , extracellular , depolarization , dentate gyrus , electrophysiology , biophysics , hippocampal formation , stimulation , granule (geology) , patch clamp , sodium channel , analytical chemistry (journal) , sodium , neuroscience , biochemistry , materials science , biology , chromatography , electrical engineering , composite material , engineering , organic chemistry
1 Properties of voltage‐dependent Na + currents were investigated in forty‐two dentate granule cells (DGCs) acutely isolated from the resected hippocampus of twenty patients with therapy‐refractory temporal lobe epilepsy (TLE) using the whole‐cell patch‐clamp technique. 2 Depolarizing voltage commands elicited large, rapidly activating and inactivating Na + currents (140 pS μm −2 ; 163 m m extracellular Na + ) that were reduced in amplitude by lowering the Na + gradient (43 m m extracellular Na + ). At low temperatures (8‐12 °C), the time course of Na + currents slowed and could be well described by the model of Hodgkin & Huxley. 3 Na + currents were reversibly blocked by tetrodotoxin (TTX) and saxitoxin (STX) with a half‐maximal block of 4.7 and 2.6 n m , respectively. In order to reduce series resistance errors, the Na + current was partially blocked by low toxin concentrations (10‐15 n m ) in the experiments described below. Under these conditions, Na + currents showed a threshold of activation of about ‐50 mV, and the voltages of half‐maximal activation and inactivation were ‐29 and ‐55 mV, respectively. 4 The time course of recovery from inactivation could be described with a double‐exponential function (time constants, 3‐20 and 60‐200 ms). The rapid and slow time constants showed a distinct voltage dependence with maximal values around ‐55 and ‐80 mV, respectively. These properties contributed to a reduction of the Na + currents during repetitive stimulation that was more pronounced with higher stimulation frequencies and also showed a dependence on the holding potential. 5 In summary, the most striking features of DGC Na + currents were the large current density and the presence of a current component showing a slow recovery from inactivation. Our data provide a basis for comparison with properties of Na + currents in animal models of epilepsy, and for the study of drug actions in therapy‐refractory epilepsy.