TY - JOUR
T1 - Kv1.1 knock-in ataxic mice exhibit spontaneous myokymic activity exacerbated by fatigue, ischemia and low temperature
AU - Brunetti, Orazio
AU - Imbrici, Paola
AU - Botti, Fabio Massimo
AU - Pettorossi, Vito Enrico
AU - D'Adamo, Maria Cristina
AU - Valentino, Mario
AU - Zammit, Christian
AU - Mora, Marina
AU - Gibertini, Sara
AU - Di Giovanni, Giuseppe
AU - Muscat, Richard
AU - Pessia, Mauro
N1 - Funding Information:
We thank Dr. James Maylie and Dr. John P. Adelman for generously sharing their Kv1. V408A/+ ataxia mice. We thank Mauro Roscini, Massimo Pierucci, Samantha Austen and Maria Teresa Laveglia for their contributions to this study. This work was supported by COMPAGNIA di San Paolo (Turin) “Programma Neuroscienze”, Telethon ( GGP11188 ), Ministero della Salute ( GR-2009-1580433 ) and Fondazione Cassa di Risparmio di Perugia .
PY - 2012/9
Y1 - 2012/9
N2 - Episodic ataxia type 1 (EA1) is an autosomal dominant neurological disorder characterized by myokymia and attacks of ataxic gait often precipitated by stress. Several genetic mutations have been identified in the Shaker-like K+ channel Kv1.1 (KCNA1) of EA1 individuals, including V408A, which result in remarkable channel dysfunction. By inserting the heterozygous V408A, mutation in one Kv1.1 allele, a mouse model of EA1 has been generated (Kv1.1V408A/+). Here, we investigated the neuromuscular transmission of Kv1.1V408A/+ ataxic mice and their susceptibility to physiologically relevant stressors. By using in vivo preparations of lateral gastrocnemius (LG) nerve-muscle from Kv1.1+/+ and Kv1.1V408A/+ mice, we show that the mutant animals exhibit spontaneous myokymic discharges consisting of repeated singlets, duplets or multiplets, despite motor nerve axotomy. Two-photon laser scanning microscopy from the motor nerve, ex vivo, revealed spontaneous Ca2+ signals that occurred abnormally only in preparations dissected from Kv1.1V408A/+ mice. Spontaneous bursting activity, as well as that evoked by sciatic nerve stimulation, was exacerbated by muscle fatigue, ischemia and low temperatures. These stressors also increased the amplitude of compound muscle action potential. Such abnormal neuromuscular transmission did not alter fiber type composition, neuromuscular junction and vascularization of LG muscle, analyzed by light and electron microscopy. Taken together these findings provide direct evidence that identifies the motor nerve as an important generator of myokymic activity, that dysfunction of Kv1.1 channels alters Ca2+ homeostasis in motor axons, and also strongly suggest that muscle fatigue contributes more than PNS fatigue to exacerbate the myokymia/neuromyotonia phenotype. More broadly, this study points out that juxtaparanodal K+ channels composed of Kv1.1 subunits exert an important role in dampening the excitability of motor nerve axons during fatigue or ischemic insult.
AB - Episodic ataxia type 1 (EA1) is an autosomal dominant neurological disorder characterized by myokymia and attacks of ataxic gait often precipitated by stress. Several genetic mutations have been identified in the Shaker-like K+ channel Kv1.1 (KCNA1) of EA1 individuals, including V408A, which result in remarkable channel dysfunction. By inserting the heterozygous V408A, mutation in one Kv1.1 allele, a mouse model of EA1 has been generated (Kv1.1V408A/+). Here, we investigated the neuromuscular transmission of Kv1.1V408A/+ ataxic mice and their susceptibility to physiologically relevant stressors. By using in vivo preparations of lateral gastrocnemius (LG) nerve-muscle from Kv1.1+/+ and Kv1.1V408A/+ mice, we show that the mutant animals exhibit spontaneous myokymic discharges consisting of repeated singlets, duplets or multiplets, despite motor nerve axotomy. Two-photon laser scanning microscopy from the motor nerve, ex vivo, revealed spontaneous Ca2+ signals that occurred abnormally only in preparations dissected from Kv1.1V408A/+ mice. Spontaneous bursting activity, as well as that evoked by sciatic nerve stimulation, was exacerbated by muscle fatigue, ischemia and low temperatures. These stressors also increased the amplitude of compound muscle action potential. Such abnormal neuromuscular transmission did not alter fiber type composition, neuromuscular junction and vascularization of LG muscle, analyzed by light and electron microscopy. Taken together these findings provide direct evidence that identifies the motor nerve as an important generator of myokymic activity, that dysfunction of Kv1.1 channels alters Ca2+ homeostasis in motor axons, and also strongly suggest that muscle fatigue contributes more than PNS fatigue to exacerbate the myokymia/neuromyotonia phenotype. More broadly, this study points out that juxtaparanodal K+ channels composed of Kv1.1 subunits exert an important role in dampening the excitability of motor nerve axons during fatigue or ischemic insult.
KW - Ataxia
KW - Ca signals
KW - Fatigue
KW - Ischemia
KW - KCNA1
KW - Kv1.1
KW - Myokymia
KW - Sciatic nerve
KW - Stress
KW - Voltage-gated potassium channel
UR - http://www.scopus.com/inward/record.url?scp=84862128116&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84862128116&partnerID=8YFLogxK
U2 - 10.1016/j.nbd.2012.05.002
DO - 10.1016/j.nbd.2012.05.002
M3 - Article
C2 - 22609489
AN - SCOPUS:84862128116
SN - 0969-9961
VL - 47
SP - 310
EP - 321
JO - Neurobiology of Disease
JF - Neurobiology of Disease
IS - 3
ER -