Predominant Interactions between μ-Conotoxin Arg-13 and the Skeletal Muscle Na+Channel Localized by Mutant Cycle Analysis†

Biopsies of human skeletal muscle were analyzed by an in vitro contracture test (IVCT) for responsiveness to a halothane challenge: noncontracting (nonresponsive; IVCT-) and contracting (IVCT+). A muscle biopsy that is IVCT+ indicates potential malignant hyperthermia (MH) susceptibility. Primary cultures were grown from portions of the skeletal muscle biopsies, and voltage-activated currents were measured by whole cell recording in the presence or absence of 2-5 microM intracellular arachidonic or oleic acids. In untreated IVCT- cells, Na+ currents were predominantly tetrodotoxin (TTX) insensitive, indicating that most of the current was carried through the embryonic SkM2 isoform of the Na+ channel. Inclusion of fatty acids in the recording pipette of IVCT- cells produced an increase in voltage-activated Na+ currents during 20 min of recording. Approximately 70% of currents in fatty acid-treated cells were TTX sensitive, indicating activation of the adult SkM1 isoform of the Na+ channel. In contrast to IVCT- cells, IVCT+ cells expressed Na+ currents that were predominantly TTX sensitive even in the absence of added fatty acid, thus showing a relatively large baseline functional expression of SkM1 channels. Addition of fatty acids to the recording pipette produced little further change in the magnitude or TTX sensitivity of the whole cell currents in IVCT+ cells, suggesting altered functional regulation of Na+ channels in MH muscle.

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Two E-Boxes Are the Focal Point of Muscle-specific Skeletal Muscle Type 1 Na+Channel Gene Expression

Journal of Biological Chemistry ◽

10.1074/jbc.273.18.11327 ◽

1998 ◽

Vol 273 (18) ◽

pp. 11327-11334 ◽

Cited By ~ 14

Author(s):

Susan D. Kraner ◽

Mark M. Rich ◽

Roland G. Kallen ◽

Robert L. Barchi

Keyword(s):

Gene Expression ◽

Skeletal Muscle ◽

Focal Point ◽

Na Channel ◽

Muscle Type ◽

Channel Gene ◽

E Boxes

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Na+ channel mis-expression accelerates K+ channel development in embryonic Xenopus laevis skeletal muscle.

The Journal of Physiology ◽

10.1113/jphysiol.1994.sp020370 ◽

1994 ◽

Vol 480 (3) ◽

pp. 405-410 ◽

Cited By ~ 34

Author(s):

P Linsdell ◽

W J Moody

Keyword(s):

Skeletal Muscle ◽

Xenopus Laevis ◽

K Channel ◽

Na Channel ◽

Channel Development

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Na channel distribution in vertebrate skeletal muscle.

The Journal of General Physiology ◽

10.1085/jgp.87.6.907 ◽

1986 ◽

Vol 87 (6) ◽

pp. 907-932 ◽

Cited By ~ 49

Author(s):

J H Caldwell ◽

D T Campbell ◽

K G Beam

Keyword(s):

Skeletal Muscle ◽

Current Density ◽

Sharp Decrease ◽

Na Channel ◽

Na Current ◽

Na Currents ◽

Current Densities ◽

Kinetics Of ◽

A Current ◽

Vertebrate Skeletal Muscle

The loose patch voltage clamp has been used to map Na current density along the length of snake and rat skeletal muscle fibers. Na currents have been recorded from (a) endplate membrane exposed by removal of the nerve terminal, (b) membrane near the endplate, (c) extrajunctional membrane far from both the endplate and the tendon, and (d) membrane near the tendon. Na current densities recorded directly on the endplate were extremely high, exceeding 400 mA/cm2 in some patches. The membrane adjacent to the endplate has a current density about fivefold lower than that of the endplate, but about fivefold higher than the membrane 100-200 micron from the endplate. Small local variations in Na current density are recorded in extrajunctional membrane. A sharp decrease in Na current density occurs over the last few hundred micrometers from the tendon. We tested the ability of tetrodotoxin to block Na current in regions close to and far from the endplate and found no evidence for toxin-resistant channels in either region. There was also no obvious difference in the kinetics of Na current in the two regions. On the basis of the Na current densities measured with the loose patch clamp, we conclude that Na channels are abundant in the endplate and near-endplate membrane and are sparse close to the tendon. The current density at the endplate is two to three orders of magnitude higher than at the tendon.

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Mechanisms underlying a life-threatening skeletal muscle Na+channel disorder

The Journal of Physiology ◽

10.1113/jphysiol.2011.207977 ◽

2011 ◽

Vol 589 (13) ◽

pp. 3115-3124 ◽

Cited By ~ 10

Author(s):

Dina Simkin ◽

Isabelle Léna ◽

Pierre Landrieu ◽

Laurence Lion-François ◽

Damien Sternberg ◽

...

Keyword(s):

Skeletal Muscle ◽

Na Channel ◽

Life Threatening

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Glutamine transport and metabolism in denervated rat skeletal muscle

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1990.259.2.e148 ◽

1990 ◽

Vol 259 (2) ◽

pp. E148-E154 ◽

Cited By ~ 3

Author(s):

H. S. Hundal ◽

P. Babij ◽

P. W. Watt ◽

M. R. Ward ◽

M. J. Rennie

Keyword(s):

Skeletal Muscle ◽

Membrane Potential ◽

Maximal Activity ◽

Resting Membrane Potential ◽

Na Channel ◽

Synthetase Activity ◽

Glutamine Synthetase Activity ◽

Rat Skeletal Muscle ◽

Glutamine Transport ◽

Recovery Of Vmax

Rat skeletal muscle glutamine fell by 40% from 4.18 to 2.5 mumols/g wet weight (P less than 0.01) after 4 days of denervation. Over the same period net glutamine efflux from denervated hindlimbs [i.e., arteriovenous (a-v) concentration differences x blood flow] increased 3.5-fold (from -6.72 +/- 1.73 to -26 +/- 4.81 nmol.min-1.g-1, P less than 0.001). Gastrocnemius glutamine synthetase activity fell 48% after denervation (from 475 +/- 81 to 248 +/- 39 nmol.min-1.g-1, P less than 0.001), but glutaminase activity was not significantly altered (17 nmol.min-1.g-1). The maximal activity (Vmax) of the unidirectional Na(+)-dependent glutamine transporter (system Nm) was depressed by 45% from 1,020 +/- 104 to 571 +/- 9 nmol.min-1.g-1 (P less than 0.01), but the concentration at which transport was half maximal (Km) was not significantly altered (control 8.1 +/- 0.6 mM; denervated 6.52 +/- 0.12). Hindlimb denervation resulted in an increase of intramuscular Na+ by 17% and a fall of K+ by 12%, and the resting membrane potential in isolated muscles decreased from -75 +/- 10 to -59.5 +/- 5.5 mV. Membrane potential of perfused denervated muscle, isolated after acute addition of the Na+ channel blocker tetrodotoxin (TTX, 3 microM), repolarized to -66.4 +/- 3.2 mV. In perfused denervated preparations TTX caused an acute recovery of Vmax of unidirectional glutamine transport to 848 +/- 75 nmol.min-1.g-1; Km was unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

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