Shal/K(v)4 channels are required for maintaining excitability during repetitive firing and normal locomotion in Drosophila.
BACKGROUND
Rhythmic behaviors, such as walking and breathing, involve the coordinated activity of central pattern generators in the CNS, sensory feedback from the PNS, to motoneuron output to muscles. Unraveling the intrinsic electrical properties of these cellular components is essential to understanding this coordinated activity. Here, we examine the significance of the transient A-type K(+) current (I(A)), encoded by the highly conserved Shal/K(v)4 gene, in neuronal firing patterns and repetitive behaviors. While I(A) is present in nearly all neurons across species, elimination of I(A) has been complicated in mammals because of multiple genes underlying I(A), and/or electrical remodeling that occurs in response to affecting one gene.


RESULTS
In Drosophila, the single Shal/K(v)4 gene encodes the predominant I(A) current in many neuronal cell bodies. Using a transgenically expressed dominant-negative subunit (DNK(v)4), we show that I(A) is completely eliminated from cell bodies, with no effect on other currents. Most notably, DNK(v)4 neurons display multiple defects during prolonged stimuli. DNK(v)4 neurons display shortened latency to firing, a lower threshold for repetitive firing, and a progressive decrement in AP amplitude to an adapted state. We record from identified motoneurons and show that Shal/K(v)4 channels are similarly required for maintaining excitability during repetitive firing. We then examine larval crawling, and adult climbing and grooming, all behaviors that rely on repetitive firing. We show that all are defective in the absence of Shal/K(v)4 function. Further, knock-out of Shal/K(v)4 function specifically in motoneurons significantly affects the locomotion behaviors tested.


CONCLUSIONS
Based on our results, Shal/K(v)4 channels regulate the initiation of firing, enable neurons to continuously fire throughout a prolonged stimulus, and also influence firing frequency. This study shows that Shal/K(v)4 channels play a key role in repetitively firing neurons during prolonged input/output, and suggests that their function and regulation are important for rhythmic behaviors.
Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America.
Yong
Y
Ping
Girma
G
Waro
Ashley
A
Licursi
Sarah
S
Smith
Dai-An
DA
Vo-Ba
Susan
S
Tsunoda
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D030801:Animals, Genetically Modified; D029721:Drosophila Proteins / Q000502:physiology*; D004331:Drosophila melanogaster / Q000502:physiology*; D008124:Locomotion / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D010507:Periodicity; D051672:Shal Potassium Channels / Q000502:physiology*; D009435:Synaptic Transmission
D029721:Drosophila Proteins; D051672:Shal Potassium Channels; C497024:Shal protein, Drosophila
Neuron. 2003 Jan 9;37(1):109-20
12526777
Science. 1990 May 4;248(4955):599-603
2333511
Genetics. 1993 Mar;133(3):581-92
8454205
J Neurophysiol. 2005 Nov;94(5):3601-17
16049145
Proc Natl Acad Sci U S A. 1991 May 15;88(10):4386-90
2034678
Cell. 2002 Nov 1;111(3):319-30
12419243
Mol Cell Neurosci. 2009 Sep;42(1):33-44
19463952
Neuron. 2010 Aug 12;67(3):373-80
20696376
J Neurosci. 1999 Jul 1;19(13):5311-21
10377342
Development. 2003 Nov;130(22):5385-400
13129849
Proc Natl Acad Sci U S A. 2006 Aug 1;103(31):11584-8
16855048
Proc Natl Acad Sci U S A. 2001 Apr 24;98(9):5276-81
11309504
J Physiol (Paris). 1985;80(4):275-82
2422356
J Neurosci. 1988 Dec;8(12):4765-79
3199204
Science. 1992 Aug 28;257(5074):1225-30
1519059
J Neurosci. 1995 Jul;15(7 Pt 2):5209-21
7623146
Physiol Rev. 2004 Jul;84(3):803-33
15269337
Mol Cell Neurosci. 2007 Jun;35(2):383-96
17498969
Neuron. 2004 Oct 14;44(2):351-64
15473972
Trends Neurosci. 1992 May;15(5):161-6
1377421
J Neurosci. 1997 Jan 1;17(1):32-44
8987734
J Neurosci. 2006 Nov 22;26(47):12143-51
17122039
J Physiol. 1971 Feb;213(1):31-53
5575343
J Neurosci. 1985 Oct;5(10):2626-40
2413182
J Neurosci. 1995 Mar;15(3 Pt 1):1741-54
7891132
J Neurosci. 1997 Jul 1;17(13):5108-18
9185548
J Neurosci. 2000 Jun 1;20(11):4145-55
10818150
J Neurosci. 2003 Jun 1;23(11):4625-34
12805302
Neuron. 2006 Apr 6;50(1):89-100
16600858
Neuron. 2007 Jun 21;54(6):933-47
17582333
J Neurosci. 1993 Jan;13(1):167-80
8093714
Circ Res. 1998 Sep 7;83(5):560-7
9734479
Nature. 1981 Sep 17-23;293(5829):228-30
6268986
J Neurosci. 2010 Apr 7;30(14):5092-101
20371829
J Neurophysiol. 2009 Dec;102(6):3673-88
19828724
Dev Biol. 2004 May 15;269(2):459-78
15110713
Proc Natl Acad Sci U S A. 2002 Jul 23;99(15):10144-9
12114547
J Neurosci. 2003 Oct 8;23(27):9246-53
14534259
Science. 1987 May 29;236(4805):1094-8
2437657
Neuron. 1990 Jan;4(1):129-40
2310571
Neuron. 1991 Sep;7(3):471-83
1840649
J Neurosci. 2006 Jun 7;26(23):6238-48
16763031
Mol Cell Neurosci. 2010 Sep;45(1):75-83
20550966
J Neurosci. 2001 Oct 15;21(20):8004-14
11588173
Neuron. 2010 Apr 29;66(2):220-34
20434999
J Physiol. 1983 Apr;337:687-709
6308239
J Neurophysiol. 2010 Sep;104(3):1257-66
20573969
Proc Natl Acad Sci U S A. 1967 Sep;58(3):1112-9
16578662
J Neurosci. 2005 Mar 2;25(9):2348-58
15745961
J Biol Chem. 2006 Oct 13;281(41):30725-35
16899454
J Neurosci. 2005 Oct 5;25(40):9185-94
16207878
Proc Natl Acad Sci U S A. 2007 Mar 20;104(12):5199-204
17360325
Neuron. 1991 Nov;7(5):763-73
1742024
Nat Neurosci. 2010 Jan;13(1):53-9
19966842
J Neurosci. 1997 Dec 15;17(24):9642-55
9391019
J Neurosci. 2009 Jan 28;29(4):951-63
19176804
J Neurophysiol. 2004 May;91(5):2353-65
14695352
J Physiol. 2005 Nov 15;569(Pt 1):41-57
16141270
J Physiol. 2008 Mar 15;586(6):1565-79
18187474
J Neurosci. 2000 Mar 15;20(6):2104-11
10704484
Genes Dev. 1999 Oct 1;13(19):2549-61
10521399