All Phenotypes Ank1<tm1Vso> MGI Mouse

abnormal extensor digitorum longus morphology ( J:223673 )

• at 12-15 months of age, mutant EDL muscles exhibit a high frequency of fibers (57.5 +/- 4.78%) presenting large tubular aggregates (TAs) and a significantly reduced SR volume at the sarcomere A band level relative to age-matched wild-type controls

• observed TAs are variable in size and are very rarely detected in adult wild-type EDL fibers; TAs are positive for triadin, calsequestrin, and SERCA1 but negative for alpha1s-DHPR and RyR1

• in a few EDL fibers some areas of excessive contracture and myofibrillar damage/degeneration are also observed

• however, Western blot analysis revealed no significant differences in the expression levels of select SR and T-tubules proteins (triadin, SERCA1, calsequestrin, junctophillin 1 and 2, and alpha1s-DHPR) in mutant EDL at 12-15 months of age

abnormal sarcolemma morphology ( J:223673 )

• at 12-15 months of age, an Evans blue dye test revealed a significant increase in the % of Evans blue positive fibers in the mutant diaphragm, suggesting loss of sarcolemma integrity

abnormal sarcoplasmic reticulum morphology ( J:223673 )

• homozygotes show a significant reduction of longitudinal sarcoplasmic reticulum (SR) volume at the sarcomere A band level in EDL skeletal muscle fibers at both 5 and 15 months of age

• however, no significant alterations are observed in the localization and expression of select SR and T-tubule proteins at a young age (4-6 months of age) in EDL, soleus, diaphragm, and tibialis anterior muscles

abnormal skeletal muscle fiber triad morphology ( J:223673 )

• at 12-15 months of age, the regular disposition of intracellular organelles (such as triads) within contractured regions of the mutant diaphragms is abnormal with myofibrils that tend to fuse laterally

skeletal muscle fiber degeneration ( J:223673 )

• at 12-15 months of age, a few mutant EDL muscle fibers show areas of excessive contracture and myofibrillar damage/degeneration

• at this age, damage and degeneration is much more severe in the diaphragm, with 61.5 +/- 5.15% of diaphragm muscle fibers displaying contractures, unlike wild-type controls where contractures are never found

abnormal diaphragm morphology ( J:223673 )

• at 12-15 months of age, the levels of the alpha1s-DHPR protein are reduced by 15% in the mutant diaphragm relative to age-matched wild-type controls, whereas levels of other SR and T-tubules proteins (triadin, SERCA1, calsequestrin, and junctophillin 1 and 2) remain relatively unaffected

• at this age, mutant diaphragms exhibit large areas of contracture in 61.5 +/- 5.15% fibers, alternated with regions in which the length of sarcomeres is overstretched or apparently normal

• in contractured regions intermyofibrillar organelles, such as mitochondria or triads, are misplaced or missing with contracted myofibrils, which appear fused laterally with each other

impaired skeletal muscle contractility ( J:223673 )

• at 4-6 months of age, time to peak tension is significantly prolonged in mutant diaphragms but not in EDL or soleus muscles relative to wild-type controls, whereas half-relaxation time remains unaffected

• at 12-15 months of age, time to peak and half-relaxation time are significantly longer in mutant EDL muscles, whereas twitch tension and tetanus tension show no significant differences relative to wild-type EDL

• at 12-15 months, time to peak and half-relaxation time are significantly longer in mutant diaphragms and twitch and tetanic tension are reduced relative to wild-type diaphragms

• at 12-15 months, induction of gastrocnemius contraction via sciatic nerve stimulation revealed normal torque development but slower twitch kinetics, as shown by a significantly prolonged twitch time to peak relative to wild-type controls

• no difference in contractile function is noted in mutant soleus muscle at 12-15 months relative to wild-type controls

abnormal muscle electrophysiology ( J:223673 )

• at 12-15 months of age, mutant diaphragm muscle fibers show significant alterations in the resting membrane potential (RMP), membrane capacitance (Cm), specific resting membrane conductance (Gm/Cm), and L-type Ca2+ current density (ICa/Cm) relative to wild-type controls, suggesting fiber atrophy, increased leak current, and affected excitation-contraction coupling

• mutant diaphragm fibers show a significant decrease of the steady-state amount of the Qgamma charge moved, Qgammamax, and a shift towards more positive potential of Vgamma but not of Qbeta parameters relative to wild-type controls

• reduced Qgamma charge and L-type Ca2+ current (indexes of affected excitation-contraction coupling) are observed in diaphragm fibers but not in other skeletal muscles

myopathy ( J:223673 )

• at 12-15 months of age, homozygotes develop a myopathy characterized by premature formation of large TAs in EDL and by structural damage of contractile elements which is especially severe in the diaphragm

impaired exercise endurance ( J:223673 )

• at 12-15 months of age, homozygotes show a drastic reduction of performance in a treadmill endurance test, running only for half the time or distance covered by wild-type controls

• however, homozygotes perform similarly to wild-type controls in the grip test, indicating normal force generation at the limb level

abnormal calcium ion homeostasis ( J:223673 )

• altered sarcolemmal electrophysiological features, such as a depolarized RMP and an increased specific membrane conductance, Gm/Cm, paralleled by a reduced Qgamma charge and L-type Ca2+ current density (ICa/Cm), together with the Evans blue dye test suggest an increased intracellular Ca2+ concentration, likely due to a leaky sarcolemma