title: Properties of two voltage-activated potassium currents in acutely isolated juvenile rat dentate gyrus granule cells.
abstract: 1. The properties of outward currents were investigated in acutely isolated dentate gyrus granule cells at postnatal ages of day 5-7, 10-14, 18-24 (P5-7, P10-14, P18-24) and at adulthood (2-3 mo), with the use of the whole-cell patch-clamp technique. 2. Kinetic analysis and pharmacological properties showed that an A-type K+ current (IA) and a delayed rectifier current (IK) were present in these cells. 3. IA in P10-14 cells activated and inactivated rapidly with a decay time constant of 7.5 +/- 2.1 (SD) ms with command pulses to +30 mV. The removal of inactivation was monoexponential with a time constant of 23.1 ms (holding potential, -50 mV; conditioning voltage steps of varying duration to -110 mV). V 1/2 of the Boltzmann function describing steady-state inactivation was -65.1 +/- 1.8 mV with a slope factor of -6.0. IA was sensitive to 5 mM 4-aminopyridine (4-AP) but not to 10 mM tetraethylammonium (TEA). 4. IK in P10-14 cells displayed a voltage-dependent activation time constant (4.3 +/- 0.8 ms for command pulses to +30 mV and 16.2 +/- 2.4 for command pulses to -10 mV) and a double-exponential decay (time constants 194 +/- 21 and 1,625 +/- 254 ms). The rate constant of removal of inactivation was 332.1 ms. IK showed a reduction by 61.4 +/- 5.3% with 10 mM TEA and was partially blocked by 5 mM 4-AP in a subpopulation of cells. 5. Whereas IA remained stable over time, IK showed a substantial reduction of current amplitude by 67% after 30 min of cell perfusion through the patch pipette. The time course of this reduction was monoexponential with a time constant of 6.9 min and was partly due to a shift in V1/2 of the steady-state inactivation from -79.2 to -99.6 mV. 6. IA and IK remained stable with respect to kinetic properties during ontogenesis. However, the relative contribution and pharmacological properties of the investigated K+ currents varied with age. Although IA dominated in P5-7 cells, IK was prominent in most older cells. Five millimolars 4-AP reduced IA by 40.7 +/- 26.7% in P5-7 cells and blocked IA completely in 80% of investigated P10-14 cells. Similar changes were observed for the effects of 4-AP on IK (18.7% depression in the age group P5-8, 46.1% in the age group P10-14, and 45.7% in adult animals).
authors: Institut für Neurophysiologie, Universität zu Köln, Germany.
authors: H
authors: H
authors: Beck
authors: E
authors: E
authors: Ficker
authors: U
authors: U
authors: Heinemann
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000375:Aging / Q000502:physiology; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology; D001464:Barium / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D004594:Electrophysiology; D006624:Hippocampus / Q000166:cytology / Q000254:growth & development / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D002104:Cadmium; D001464:Barium; D015761:4-Aminopyridine