| 10634854 |
Kang J, Huguenard JR, Prince DA: Voltage-gated potassium channels activated during action potentials in layer V neocortical pyramidal neurons. J Neurophysiol. 2000 Jan;83(1):70-80.
To investigate voltage-gated potassium channels underlying action potentials (APs), we simultaneously recorded neuronal APs and single K (+) channel activities, using dual patch-clamp recordings (1 whole cell and 1 cell-attached patch) in single-layer V neocortical pyramidal neurons of rat brain slices. A fast voltage-gated K (+) channel with a conductance of 37 pS (K (f)) opened briefly during AP repolarization. Activation of K (f) channels also was triggered by patch depolarization and did not require Ca (2+) influx. Activation threshold was about -20 mV and inactivation was voltage dependent. Mean duration of channel activities after single APs was 6.1 +/- 0.6 ms (mean +/- SD) at resting membrane potential (-64 mV), 6.7 +/- 0.7 ms at -54 mV, and 62 +/- 15 ms at -24 mV. The activation and inactivation properties suggest that K (f) channels function mainly in AP repolarization but not in regulation of firing. K (f) channels were sensitive to a low concentration of tetraethylammonium (TEA, 1 mM) but not to charybdotoxin (ChTX, 100 nM). Activities of A-type channels (K (A)) also were observed during AP repolarization. K (A) channels were activated by depolarization with a threshold near -45 mV, suggesting that K (A) channels function in both repolarization and timing of APs. Inactivation was voltage dependent with decay time constants of 32 +/- 6 ms at -64 mV (rest), 112 +/- 28 ms at -54 mV, and 367 +/- 34 ms at -24 mV. K (A) channels were localized in clusters and were characterized by steady-state inactivation, multiple subconductance states (36 and 19 pS), and inhibition by 5 mM 4-aminopyridine (4-AP) but not by 1 mM TEA. A delayed rectifier K (+) channel (K (dr)) with a unique conductance of 17 pS was recorded from cell-attached patches with TEA/4-AP-filled pipettes. K (dr) channels were activated by depolarization with a threshold near -25 mV and showed delayed long-lasting activation. K (dr) channels were not activated by single action potentials. Large conductance Ca (2+)-activated K (+) (BK) channels were not triggered by neuronal action potentials in normal slices and only opened as neuronal responses deteriorated (e.g., smaller or absent spikes) and in a spike-independent manner. This study provides direct evidence for different roles of various K (+) channels during action potentials in layer V neocortical pyramidal neurons. K (f) and K (A) channels contribute to AP repolarization, while K (A) channels also regulate repetitive firing. K (dr) channels also may function in regulating repetitive firing, whereas BK channels appear to be activated only in pathological conditions. |
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