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  • 1
    Electronic Resource
    Electronic Resource
    Relation between action potential duration and mechanical activity on rat diaphragm fibers (1987)
    Springer
    Pflügers Archiv 410 (1987), S. 394-400 
    Details
    ISSN: 1432-2013
    Keywords: Mammalian skeletal muscle ; 3,4-Diaminopyridine ; Tetraethylammonium ; Potassium channels blockers ; Mechanical activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The aim of this work was to study the electrical and mechanical properties of small bundles of rat diaphragm muscle treated with two blockers of the delayed potassium rectification channels: 3,4-diaminopyridine (3,4-DAP, 2.5 mM) and tetraethylammonium (TEA, 20 mM). Twitch tension was significantly potentiated by TEA and 3,4-DAP (39% and 59% respectively). Maximal tetanic tension was not affected by both drugs. The voltage dependence of the tension vs the resting membrane potential was shifted to lower values in TEA and 3,4-DAP. 3,4-DAP increased the caffeine contracture tension (2.5–10 mM) and lowered the caffeine contracture threshold. The duration of the action potential (measured at the level of −40 mV) was increased by TEA and 3,4-DAP solutions. This change was a consequence of the decrease in the rat of repolarization of the action potential. In addition, TEA reduced the amplitude and the rate of rise of the action potential. We suggested that the increment in the duration of the action potential and the shift of the mechanical threshold to more negative values of membrane potential might be the factors involved in the twitch potentiation induced by the TEA and 3,4-DAP solutions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00586516
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  • 2
    Electronic Resource
    Electronic Resource
    Calcium regulates L-Type Ca2+ channel expression in rat skeletal muscle cells (1999)
    Springer
    Pflügers Archiv 438 (1999), S. 649-655 
    Details
    ISSN: 1432-2013
    Keywords: Calcium Gating current Dihydropyridine receptor L-type calcium channel Skeletal muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Primary skeletal muscle cells were cultured in a normal- (1.8 mM) or high- (4.8 mM) Ca2+ culture medium to determine whether Ca2+ modulates the number of L-type Ca2+ channels. Skeletal myoballs cultured in a normal medium showed, when exposed to a high extracellular [Ca2+], ([Ca2+]e) a transient increase in intracellular [Ca2+] ([Ca2+]i) from a resting concentration of 60 to 160 nM. By day 3, however, when the experiments were made, [Ca2+]i no longer differed from control (pre-exposure to high Ca2+). The maximum charge movements in myoballs incubated in 1.8 and 4.8 mM were 16.4±1.05 (n=56) and 24.1±1.18 nC/µF (n=58; P〈0.01), respectively, and peak Ca2+ currents at 20 mV were –10.8±1.09 (n=46) and –12.8±0.75 nA/µF (n=82), respectively (P〉0.05). The tail current amplitudes in 1.8 and 4.8 mM Ca2+-treated cells were –9.3±1.23 and –14.2±1.37 nA/µF (P〈0.05), respectively, at 10 mV and –15.3±1.76 and –23.6±2.02 nA/µF (P〈0.05), respectively at 60 mV. The maximum binding of [3H]PN200-110 (a radioligand specific for L-type Ca2+ channel α1 subunits) in myoballs cultured in 1.8 and 4.8 mM [Ca2+]e was 1.34±0.23 and 3.2±0.63 pmol/mg protein (n=8; P〈0.02), respectively. The increase in [Ca2+]i associated with the increases in charge movements, tail currents and the number of L-type Ca2+ channel α1 subunits in skeletal muscle cells cultured in high [Ca2+]e support the concept that extracellular Ca2+ influx modulates the expression of L-type Ca2+ channels in skeletal muscle cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004249900087
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  • 3
    Electronic Resource
    Electronic Resource
    Sarcoplasmic Reticulum Ca2+ Release in Rat Slow- and Fast-Twitch Muscles (1996)
    Springer
    The journal of membrane biology 151 (1996), S. 123-130 
    Details
    ISSN: 1432-1424
    Keywords: Key words: Skeletal muscle — Sarcoplasmic reticulum — Calcium release — Soleus — Slow-twitch muscle — Dihydropyridine receptor — Ryanodine receptor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. The same isoform of ryanodine receptor (RYR1) is expressed in both fast and slow mammalian skeletal muscles. However, differences in contractile activation and calcium release kinetics in intact and skinned fibers have been reported. In this work, intracellular Ca2+ transients were measured in soleus and extensor digitorum longus (EDL) single muscle fibers using mag-fura-2 (K D for Ca2+= 49 μm) as Ca2+ fluorescent indicator. Fibers were voltage-clamped at V h =−90 mV and sarcoplasmic reticulum calcium release was measured at the peak (a) and at the end (b) of 200 msec pulses at +10 mV. Values of a-b and b were assumed to correspond to Ca2+-gated and voltage-gated Ca2+ release, respectively. Ratios (b/a-b) in soleus and EDL fibers were 0.41 ± 0.05 and 1.01 ± 0.13 (n= 12), respectively. This result suggested that the proportion of dihydropyridine receptor (DHPR)-linked and unlinked RYRs is different in soleus and EDL muscle. The number of DHPR and RYR were determined by measuring high-affinity [3H]PN200-110 and [3H]ryanodine binding in soleus and EDL rat muscle homogenates. The B max values corresponded to a PN200-110/ryanodine binding ratio of 0.34 ± 0.05 and 0.92 ± 0.11 for soleus and EDL muscles (n= 4–8), respectively. These data suggest that soleus muscle has a larger calcium-gated calcium release component and a larger proportion of DHPR-unlinked RYRs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002329900063
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  • 4
    Electronic Resource
    Electronic Resource
    Dihydropyridine Receptor-Ryanodine Receptor Uncoupling in Aged Skeletal Muscle (1997)
    Springer
    The journal of membrane biology 157 (1997), S. 247 -253 
    Details
    ISSN: 1432-1424
    Keywords: Key words: Skeletal muscle — Ryanodine receptor — Dihydropyridine receptor — Aging — Excitation-contraction coupling —Soleus muscle —Extensor digitorum longus muscle — Calcium release
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. The mechanisms underlying skeletal muscle functional impairment and structural changes with advanced age are only partially understood. In the present study, we support and expand our theory about alterations in sarcolemmal excitation-sarcoplasmic reticulum Ca2+ release-contraction uncoupling as a primary skeletal muscle alteration and major determinant of weakness and fatigue in mammalian species including humans. To test the hypothesis that the number of RYR1 (ryanodine receptor) uncoupled to DHPR (dihydropyridine receptor) increases with age, we performed high-affinity ligand binding studies in soleus, extensor digitorum longus (EDL) and in a pool of several skeletal muscles consisting of a mixture of fast- and slow-twitch muscle fibers in middle-aged (14-month) and old (28-months) Fisher 344 Brown Norway F1 hybrids rats. The number of DHPR, RYR1, the coupling between both receptors expressed as the DHPR/RYR1 maximum binding capacity, and their dissociation constant for high-affinity ligands were measured. The DHPR/RYR1 ratio was significantly reduced in the three groups of muscles (pool: 1.03 ± 0.15 and 0.80 ± 0.11, soleus: 0.44 ± 0.12 and 0.26 ± 0.10, and EDL: 0.95 ± 0.14 and 0.68 ± 0.10, for middle-aged and old muscles, respectively). These data support the concept that DHPR-RYR1 uncoupling results in alterations in the voltage-gated sarcoplasmic reticulum Ca2+ release mechanism, decreases in myoplasmic Ca2+ elevation in response to sarcolemmal depolarization, reduced Ca2+ supply to contractile proteins and reduced contraction force with aging.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002329900233
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  • 5
    Electronic Resource
    Electronic Resource
    Excitation-calcium release uncoupling in aged single human skeletal muscle fibers (1995)
    Springer
    The journal of membrane biology 148 (1995), S. 211-222 
    Details
    ISSN: 1432-1424
    Keywords: Dihydropyridine receptor ; Muscle contraction ; Calcium release ; Voltage-clamp ; Calcium channels ; Muscle weakness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The biological mechanisms underlying decline in muscle power and fatigue with age are not completely understood. The contribution of alterations in the excitation-calcium release coupling in single muscle fibers was explored in this work. Single muscle fibers were voltage-clamped using the double Vaseline gap technique. The samples were obtained by needle biopsy of the vastus lateralis (quadriceps) from 9 young (25–35 years; 25.9 ± 9.1; 5 female and 4 male) and 11 old subjects (65–75 years; 70.5 ± 2.3; 6 f, 5 m). Data were obtained from 36 and 39 fibers from young and old subjects, respectively. Subjects included in this study had similar physical activity. Denervated and slow-twitch muscle fibers were excluded from this study. A significant reduction of maximum charge movement (Qmax) and DHP-sensitive Ca current were recorded in muscle fibers from the 65–75 group. Qmax values were 7.6 ± 0.9 and 3.2 ± 0.3 nC/μF for young and old muscle fibers, respectively (P 〈 0.01). No evidences of charge inactivation or interconversion (charge 1 to charge 2) were found. The peak Ca current was (−)4.7 ± 0.08 and (−)2.15 ± 0.11 μA/μF for young and old fibers, respectively (P 〈 0.01). The peak calcium transient studied with mag-fura-2 (400 μm) was 6.3 ± 0.4 μm and 4.2 ± 0.3 μm for young and old muscle fibers, respectively. Caffeine (0.5 mm) induced potentiation of the peak calcium transient in both groups. The decrease in the voltage-/ Ca-dependent Ca release ratio in old fibers (0.18 ± 0.02) compared to young fibers (0.47 ± 0.03) (P 〈 0.01), was recorded in the absence of sarcoplasmic reticulum calcium depletion. These data support a significant reduction of the amount of Ca available for triggering mechanical responses in aged skeletal muscle and, the reduction of Ca release is due to DHPR-ryanodine receptor uncoupling in fast-twitch fibers. These alterations can account, at least partially for the skeletal muscle function impairment associated with aging.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00235039
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  • 6
    Electronic Resource
    Electronic Resource
    The Specific Force of Single Intact Extensor Digitorum Longus and Soleus Mouse Muscle Fibers Declines with Aging (2000)
    Springer
    The journal of membrane biology 178 (2000), S. 175-183 
    Details
    ISSN: 1432-1424
    Keywords: Key words: Aging — Skeletal muscle — Single fiber —Soleus—Extensor digitorum longus—Flexor digitorum brevis— Excitation-contraction coupling — Sarcopenia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. In the present study we measured, for the first time, the isometric specific force (SF, force normalized to cross sectional area) generated by single intact fibers from fast- (extensor digitorum longus, EDL) and slow-twitch (soleus) muscles from young adult (2–6), middle-aged (12–14) and old (20–24 month-old) mice. SF has also been measured in single intact flexor digitorum brevis fibers from young mice. Muscle fibers have been classified into fast- or slow-twitch based on the contraction kinetics. Maximum SF recorded in EDL and soleus fibers from young and middle-aged mice did not differ significantly. A significant age-dependent decline in maximum SF was recorded in EDL and soleus fibers from young or middle-aged to old mice. The SF was 377 ± 18, 417 ± 20 and 279 ± 18 kPa for EDL fibers from young, middle-aged and old mice, respectively and 397 ± 17, 405 ± 24 and 320 ± 33 kPa for soleus fibers from age-matched mice, respectively. The frequency needed to elicit maximum force in EDL and soleus fibers from middle-aged to old mice did not differ significantly. In conclusion, the specific force developed by both fast and slow-twitch single intact muscle fibers declines with aging and more significantly in the former.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002320010025
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