Kinetic properties and functional dynamics of sodium channels during repetitive spiking in a slow pacemaker neuron.
We examined the kinetic properties of voltage-gated Na(+) channels and their contribution to the repetitive spiking activity of medullary raphé neurons, which exhibit slow pacemaking and strong spiking adaptation. The study is based on a combination of whole-cell patch-clamp, modeling and real-time computation. Na(+) currents were recorded from neurons in brain slices obtained from male and female neonatal rats, using voltage-clamp protocols designed to reduce space-clamp artifacts and to emphasize functionally relevant kinetic features. A detailed kinetic model was formulated to explain the broad range of transient and stationary voltage-dependent properties exhibited by Na(+) currents. The model was tested by injecting via dynamic clamp a model-based current as a substitute for the native TTX-sensitive Na(+) currents, which were pharmacologically blocked. The model-based current reproduced well the native spike shape and spiking frequency. The dynamics of Na(+) channels during repetitive spiking were indirectly examined through this model. By comparing the spiking activities generated with different kinetic models in dynamic-clamp experiments, we determined that state-dependent slow inactivation contributes significantly to spiking adaptation. Through real-time manipulation of the model-based current, we established that suprathreshold Na(+) current mainly controls spike shape, whereas subthreshold Na(+) current modulates spiking frequency and contributes to the pacemaking mechanism. Since the model-based current was injected in the soma, the results also suggest that somatic Na(+) channels are sufficient to establish the essential spiking properties of raphé neurons in vitro.
Milescu
Lorin S
LS
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA. Lorin_Milescu@hms.harvard.edu
Yamanishi
Tadashi
T
Ptak
Krzysztof
K
Smith
Jeffrey C
JC
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D001683:Biological Clocks / Q000502:physiology*; D055592:Biophysical Phenomena / Q000502:physiology*; D019256:Cadmium Chloride / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D008959:Models, Neurological; D009474:Neurons / Q000502:physiology*; D017711:Nonlinear Dynamics; D018408:Patch-Clamp Techniques / Q000379:methods; D011336:Probability; D011903:Raphe Nuclei / Q000166:cytology; D051381:Rats; D017207:Rats, Sprague-Dawley; D026941:Sodium Channel Blockers / Q000494:pharmacology; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors
D018691:Excitatory Amino Acid Antagonists; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D013779:Tetrodotoxin; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D019256:Cadmium Chloride
J Physiol. 1996 May 15;493 ( Pt 1):83-97
8735696
J Neurosci. 2008 Nov 12;28(46):11768-77
19005038
J Neurosci. 1993 Jan;13(1):181-94
8380849
Nature. 1999 Jul 22;400(6742):360-3
10432113
J Gen Physiol. 2004 Nov;124(5):463-74
15504897
J Neurosci. 2003 Jun 15;23(12):4899-912
12832512
J Neurophysiol. 1993 Mar;69(3):992-5
8463821
Biophys J. 1999 Apr;76(4):1868-85
10096885
J Neurophysiol. 2002 Nov;88(5):2242-50
12424266
Biophys J. 1999 Feb;76(2):846-60
9929486
J Neurosci. 2010 Jun 2;30(22):7740-8
20519549
Neuron. 2006 Jan 19;49(2):257-70
16423699
J Neurosci. 2010 May 26;30(21):7401-13
20505107
J Physiol. 1999 Dec 1;521 Pt 2:467-82
10581316
J Neurosci. 2003 Nov 12;23(32):10338-50
14614093
J Gen Physiol. 1984 Oct;84(4):505-34
6094703
Pflugers Arch. 1990 Jul;416(5):493-500
2172914
J Neurosci. 1993 Feb;13(2):660-73
8381170
Neuron. 2002 Feb 14;33(4):587-600
11856532
Nat Neurosci. 2003 May;6(5):476-83
12679783
Neuron. 2009 Dec 24;64(6):898-909
20064395
Physiol Rev. 1991 Oct;71(4):1047-80
1656476
Neuron. 1994 Apr;12(4):819-29
8161454
Neuron. 1999 Jan;22(1):73-87
10027291
Proc Natl Acad Sci U S A. 2009 Sep 29;106(39):16829-34
19805381
J Neurosci. 2000 Nov 15;20(22):8493-503
11069957
J Biol Chem. 2003 Sep 5;278(36):34320-30
12807875
J Neurophysiol. 1994 Jun;71(6):2562-5
7931536
Biophys J. 2008 Jul;95(1):66-87
18375511
Mol Pharmacol. 1991 Aug;40(2):289-98
1715017
Proc Natl Acad Sci U S A. 2006 Nov 21;103(47):17991-6
17101981
Neuron. 2007 Aug 2;55(3):449-63
17678857
Biophys J. 1981 Sep;35(3):595-614
6268217
Neuron. 1991 Nov;7(5):775-85
1660285
Physiol Rev. 2000 Apr;80(2):555-92
10747201
J Neurosci. 2009 Mar 25;29(12):3720-37
19321769
Physiol Rev. 1992 Jan;72(1):165-229
1731370
J Neurosci. 2003 Oct 22;23(29):9650-63
14573545
Nat Rev Neurosci. 2007 Jun;8(6):451-65
17514198
J Gen Physiol. 2004 Nov;124(5):445-61
15504896
Biophys J. 2001 Feb;80(2):729-37
11159440
J Neurosci. 2008 Jul 16;28(29):7260-72
18632930
Gen Physiol Biophys. 1987 Oct;6(5):409-24
2448182
Biophys J. 2005 Apr;88(4):2494-515
15681642
J Physiol. 1952 Aug;117(4):500-44
12991237