Comparison of HEGC membrane properties with those of normotopic dentate granule cells
| CGC | GC-SE | HEGC | |
|---|---|---|---|
| Resting Vm, mV | −79 ± 1 | −78 ± 1 | −70 ± 1* |
| Membrane time constant, ms | 8.1 ± 0.5 | 8.1 ± 0.4 | 9.7 ± 0.7 |
| Input resistance, MΩ | 305 ± 18 | 216 ± 16 | 282 ± 32 |
| Membrane capacitance, pF | 27.4 ± 2.5 | 40.8 ± 3.7 | 41.1 ± 4.9 |
| Action potential threshold, mV | −42 ± 2 | −41 ± 2 | −42 ± 1 |
| Action potential amplitude, mV | 157 ± 7 | 139 ± 8 | 147 ± 4 |
| Spontaneous bursting, % | 0 | 0 | 31.6 (6/19) |
| Bursting at any Vm, % | 0 | 0 | 57.9 (11/19) |
-
Values are means ± SE for 10 CGCs, 13 GC-SEs, and 19 HEGCs. Membrane currents associated with spontaneous bursting were monitored during a 5-min cell-attached recording at a holding potential of −70 mV and a temperature of 22–24°C. Seal resistance was >2 GΩ and the leak current was <4 pA. Resting Vm was measured in current-clamp mode immediately on break-in, and the membrane time constant, input resistance, and membrane capacitance were determined from the current response to a 10-mV hyperpolarization from resting Vm applied for 200 ms. The presence or absence of depolarization-evoked bursts was determined by injecting a series of currents from −0.5 to 1.9 nA in 0.1-nA increments for 1 s each. Action potential amplitude was measured from its positive to its negative peak.
-
↵* Significantly less polarized than CGCs or GC-SEs at P < 0.01 (Newman-Keuls test after 1-way ANOVA yielded P < 0.001). CGC, normotopic granule cells from control rats; GC-SE, normotopic granule cells from rats subjected to pilocarpine-induced status epilepticus; HEGC, hilar ectopic granule cells.