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  • 1
    Electronic Resource
    Electronic Resource
    Intracellular mechanism of quinidine action on muscle contraction (1984)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 326 (1984), S. 375-381 
    Details
    ISSN: 1432-1912
    Keywords: Quinidine ; Ca2+-Activated tension development of skinned fibers ; Contractile proteins ; Sarcoplasmic reticulum ; Cardiac and skeletal muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The mechanism of quinidine action on rabbit cardiac and skeletal muscle was examined with “functionally skinned” muscle-fiber preparations. By using these preparations we could correlate measurements of muscle tension with the effect of quinidine on the Ca2+ activation of the contractile proteins and on the Ca2+ uptake and release from the sarcoplasmic reticulum (SR). Effect of quinidine on the contractile proteins. Quinidine concentrations above 0.5 mmol/l increased the maximal Ca2+-activated tension development 12% for papillary muscle and 5% for soleus (slow-twitch). Adductor magnus (fast-twitch) showed no significant change. Quinidine (0.1–1.0 mmol/l) also increased the submaximal Ca2+-activated tension development for the three muscle types (papillary muscle=soleus〉adductor magnus) and shifted the [Ca2+]-tension curves to the left in a dose-dependent fashion. Effects of quinidine on the Ca 2+ uptake and release from the SR. Sarcoplasmic reticulum of skinned fibers was loaded with Ca2+ (uptake phase), then Ca2+ was released by 25 mmol/l caffeine (release phase) giving a tension transient. The area under the tension transient was used to estimate the amount of Ca2+ released. Quinidine (〉0.5 mmol/l) decreased the Ca2+ uptake (soleus〉adductor magnus〉papillary muscle) and increased the Ca2+ release [papillary muscle=soleus ≫ adductor magnus (only at 1.5 mmol/l, the highest concentration tested)] from the SR of all three muscles in a dose-dependent manner. Quinidine at low concentration (0.1 and 0.5 mmol/l) increased the caffeine-induced tension transient of papillary muscle and higher quinidine concentrations (1.0 and 1.5 mmol/l) decreased the caffeine-induced tension transient of soleus and adductor magnus during both the uptake and release phases. The decreased Ca2+ uptake of papillary muscle in 1.5 mmol/l quinidine was antagonized by increasing the free Mg2+ from 0.032 to 0.32 mmol/l. In summary, quinidine has similar mechanisms of action in all three muscles: increased Ca2+ activation of the contractile proteins, decreased Ca2+ uptake and increased Ca2+ release from the SR in “functionally skinned” muscle fibers. We conclude that quinidine-induced decreases in Ca2+ uptake by the SR could be responsible for quinidine-induced myocardial depression and that quinidine-induced increases in Ca2+ activation of the contractile proteins and Ca2+ release from the SR could be responsible for the increases in skeletal muscle contraction caused by quinidine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00501446
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of (+)-propranolol on intracellular mechanisms of contraction in striated muscle of the rabbit (1985)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 331 (1985), S. 194-201 
    Details
    ISSN: 1432-1912
    Keywords: Propranolol ; Ca2+-Activated tension development ; Skinned fibers ; Contractile proteins ; Sarcoplasmic reticulum ; Cardiac and skeletal muscles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In functionally skinned muscle fibers from the rabbit, we studied the effect of propranolol on calcium activation of the contractile proteins and, in separate experiments, on calcium uptake and release from the sarcoplasmic reticulum (SR) while measuring physiological tension. Pieces from isolated papillary muscle (PM), soleus (SL) (slowtwitch skeletal muscle), and adductor magnus (AM) (fasttwitch skeletal muscle) were homogenized (sarcolemma disrupted). A fiber bundle from PM and single fibers from SL and AM were dissected from the homogenate and mounted on a photodiode tension transducer. To study Ca2+-activated tension development of the contractile proteins, we used high EGTA (7 mmol/l) to control the free calcium concentration. To study SR function, we used five different solutions to load the calcium into the SR and to release it from the SR with 25 mmol/l caffeine, thus producing a tension transient. In general, propranolol has similar mechanisms of action in the three muscle types. Propranolol (0.1–1.0 mmol/l) increased the submaximal calcium-activated tension development in all muscles but with PM=SL 〉 AM, and this increase was correlated with increases in calcium binding to isolated troponin C. Propranolol increased the maximal calcium-activated tension development in PM and SL, but decreased that in AM. Propranolol at concentrations of 0.3–1.0 mmol/l decreased calcium uptake by the SR but did not change caclium release in any of the three muscles. In PM, however, propranolol at a concentration of 0.1 mmol/l increased calcium uptake by the SR. We conclude that propranolol induces decreases in muscle contraction mainly by decreasing calcium uptake by the SR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00634238
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  • 3
    Electronic Resource
    Electronic Resource
    Intracellular mechanisms of verapamil and diltiazem action on striated muscle of the rabbit (1988)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 338 (1988), S. 297-302 
    Details
    ISSN: 1432-1912
    Keywords: Verapamil ; Diltiazem ; Skinned striated muscle fibres ; Sarcoplasmic reticulum ; Contractile proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Skinned fibres from striated muscle were used to study the intracellular mechanisms (contractile proteins and sarcoplasmic reticulum [SR]) of action of diltiazem (DT) and verapamil (VP) on muscle contraction. Rabbit papillary muscle (PM), and the skeletal muscles adductor magnus (AM, fast-twitch) and soleus (SL, slow-twitch) were used. The muscles were skinned by homogenization and fibre bundles for PM and single fibres for AM and SL were dissected from the homogenate and mounted on photodiode force transducers. VP (0.1–3.0 mmol/l) (and to a lesser degree DT) increased Ca2+ -activated tension development of the contractile protains in PM and SL and decreased it in AM (+[4–20]%, +4%, −[14–28]%, respectively). Both drugs increased the submaximal Ca2+ -activated tension development at the order of PM = SL 〉 AM in a dose-dependent manner. The changes of half-maximal pCa50 at 1 mmol/l VP were 0.25, 0.25, and 0.15, respectively. For Ca2+ uptake and release from the SR, VP as well as DT (0.1–3.0 mmol/l) in the uptake phase decreased caffeine-induced tension transients in a dose-dependent fashion. At 0.01–3.0 mmol/l, the drugs directly induced Ca2+ release from the SR or enhanced caffeine-induced tension transients with the exception that in PM, DT attenuated caffeine-induced tension transients. Thus, VP and DT have similar intracellular mechanisms of action in striated muscle. Both drugs induce calcium release from the SR and increase Ca2+ sensitivity of the contractile proteins, and thus could be the underlying mechanisms for potentiating twitch tension, and inducing contracture in skeletal muscle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00173404
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of halothane on functionally skinned rabbit soleus muscle fibers: A correlation between tension transient and45Ca release (1980)
    Springer
    Pflügers Archiv 388 (1980), S. 63-67 
    Details
    ISSN: 1432-2013
    Keywords: Soleus muscle ; Skinned fiber ; Halothane ; Contractile proteins ; Sarcoplasmic reticulum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The mechanism(s) involved in the halothane-induced increase in skeletal muscle contraction was studied using functionally skinned soleus muscle fibers from rabbits: For the tension study, single functionally skinned fibers were individually mounted on two pairs of forceps, with one end attached to a photodiode tension transducer. Ca2+-activated tension development of the contractile proteins, and Ca2+ uptake and release from the sarcoplasmic reticulum (SR) using caffeine-induced tension transients were studied. To measure the amount of calcium, skinned fibers at 0.1 g/ml were used and 0.075 μCi45Ca/ml was spiked in the solution 3 (pCa 6.5 and 1 mM [EGTA]) which promoted rapid loading of Ca2+. Halothane (1–3%) did not change the [Ca2+]-tension relationship; 2 and 3% halothane reduced the maximum Ca2+-activated tension by 6–7%. Halothane (1–3%) added to the solution 3, reduced45Ca uptake by 3, 22 and 23%; however, the subsequent caffeine-induced tension transient and45Ca release were increased by 10–40%. During the release phase only halothane increased both caffeine-induced tension transient and45Ca release by 20–60%. The effects of halothane on the tension transient and on the45Ca release were comparable. There was no dose-response relationship to the effects of halothane on the above parameters. It is concluded that halothane affects the SR by increasing its membrane permeability to Ca2+, resulting in an increase in myoplasmic [Ca2+] and thus in the twitch tension in skeletal muscle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00582629
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  • 5
    Electronic Resource
    Electronic Resource
    Caffeine-induced calcium release from isolated sarcoplasmic reticulum of rabbit skeletal muscle (1984)
    Springer
    Pflügers Archiv 400 (1984), S. 14-21 
    Details
    ISSN: 1432-2013
    Keywords: Isolated sarcoplasmic reticulum ; Caffeine ; Ca2+ release ; Ionic strength ; Ca2+ ; Mg2+ ; ATP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The essential conditions for the Ca2+ releasing action of caffeine from isolated sarcoplasmic reticulum (SR) of rabbits were evaluated by an investigation into the effects of Ca2+, Mg2+, MgATP2−, and ATP concentration, ionic strength, and degree of loading. The heavy fraction (4,500×g) of the reticulum was used. Except for the study on degree of loading, 0.2 mg protein·ml−1 SR was loaded actively with 0.02 mM45CaCl2, resulting in 〉90 nmol·mg protein−1 at steady state, and then the effects of various parameters with or without (control) caffeine were tested. It was found that (1) caffeine induces a transient, dosedependent release of Ca2+, (2) the absolute amount of Ca2+ released by caffeine increases with the Ca2+ load of the SR, (3) increasing the ionic strength (μ) from 0.09 to 0.3 lowers the threshold concentration of caffeine, (4) the SR is refractory to a repeated challenge by a caffeine concentration causing maximal effect, (5) caffeine-induced Ca2+ release increases with increasing (a) external Ca2+ concentrations up to 5 μM total Ca2+ (or 3 μM free Ca2+) and (b) free ATP concentrations up to 0.45 mM, and (6) caffeine-induced Ca2+ release is not affected by changes of either the Mg2+ or the MgATP2− concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00670530
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of ryanodine on skinned myocardial fibers of the rabbit (1988)
    Springer
    Pflügers Archiv 411 (1988), S. 132-136 
    Details
    ISSN: 1432-2013
    Keywords: Ryanodine ; Skinned myocardial fibers ; Rabbit ; Contractile proteins ; Sarcoplasmic reticulum ; Caffeine ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Skinned fiber bundles from papillary muscle of rabbits were used to study the effects of ryanodine (1) on direct Ca2+ activation of the contractile proteins, and (2) on direct Ca2+ uptake and release from the sarcoplasmic reticulum (SR). Caffeine (25 mM) was used to release Ca2+ from the SR and to generate a tension transient. Each tension transient occurred after sequential immersion of the fiber bundles into five solutions: loading (uptake phase, [U]) and releasing (release phase, [R]). The height of free Ca2+-activated tension development of the contractile proteins, and the area of the tension transient generated by caffeine were assessed. (1) The direct free Ca2+-activated tension development of the contractile proteins was not significantly affected by ryanodine up to 0.1 mM, either at the submaximal or maximal free Ca2+ concentrations. (2) Ryanodine (1 nM–1 μM), in U, R, or in U and R, did not significantly change the immediate caffeine-induced tension transients. In the same preparation after ryanodien treatments, the second control caffeine-induced tension transients (C2, no ryanodine) were decreased in a dose-dependent manner (IC50=50, 10 nM, 10 nM for R, U, and U and R, respectively). The depression caused by ryanodine on the SR was “activity”-dependent and not readily reversible. Total calcium content in the SR of C2 was not significantly changed by small quantities of ryanodine (〈0.1 μM) and was decreased with greater amounts of ryanodine (≥0.1 μM). Thus, at low concentrations of ryanodine, the negative inotropic action is due to decrease Ca2+ release from the SR, at high concentration of ryanodine, it is due to decrease in calcium accumulation in the SR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00582305
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of halothane on Ca2+-activated tension development in mechanically disrupted rabbit myocardial fibers (1978)
    Springer
    Pflügers Archiv 375 (1978), S. 111-117 
    Details
    ISSN: 1432-2013
    Keywords: Cardiac muscle ; Skinned fibers ; Halothane ; Contractile proteins ; Regulatory proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of halothane on maximal and submaximal Ca2+-activated tension in mechanically disrupted right ventricular papillary muscle from rabbits was studied. Steady-state isometric tension generation was measured in the muscle bundle. The relaxing solution contained (in mM) [mg2+]=1, [K+]=70, [MgATP¨-]=2, [creatine phosphate¨-]=15, [EGTA total]=7 and imidazole proprionate. The contracting solution contained in addition Ca2+ in various concentrations. In all solutions ionic strength was maintained at 0.15 and pH at 7.00±0.02 at 20°C. Each fiber bundle was immersed in control solutions equilibrated with 100% N2 and test solutions equilibrated with various concentrations of halothane-N2 mixture. Increasing doses of halothane (1–4%) significantly shifted the relationship between Ca2+ and tension towards higher [Ca2+] and depressed the maximum Ca2+-activated tension. The maximum tension generated atpCa=3.8 was depressed 5% per 1% increase in halothane concentration. The percentage of maximum tension at submaximum Ca2+ concentrations (pCa=5.6–5.0) was not significantly decreased until halothane concentration was greater than 2%. It is concluded that halothane slightly but significantly depressed the interactions of contractile proteins and to a lesser degree Ca2+-activation of the regulatory proteins. The halothane-induced depression was completely reversible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00584232
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  • 8
    Electronic Resource
    Electronic Resource
    Mechanism of adenosine 3′,5′-monophosphate (cAMP)-induced increase in Ca2+ uptake by the sarcoplasmic reticulum in functionally skinned myocardial fibers (1982)
    Springer
    Pflügers Archiv 394 (1982), S. 48-54 
    Details
    ISSN: 1432-2013
    Keywords: cAMP ; Skinned myocardial fibers ; Sarcoplasmic reticulum ; Regulatory and catalytic subunits of cAMP-dependent protein kinase ; Heat-stable inhibitor of cAMP-dependent protein kinase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The increased rate of Ca2+ uptake and ATPase activity in isolated cardiac sarcoplasmic reticulum (SR) by adenosine 3′,5′-monophosphate (cAMP) has been shown to be activated by a cAMP-dependent protein kinase (cAMP kinase). Functionally skinned myocardial fiber preparations were used to study the mechanisms of cAMP action on the SR at the same time that tension was monitored. cAMP effects were studied on Ca2+-activated tension of the contractile proteins, and on Ca2+ uptake and release from the SR using caffeine-induced tension transients. Neither cyclic AMP (0.1–5 μM) nor the catalytic subunit of cAMP kinase (0.1–1 μM) (PK-C) significantly changed either the maximal or the submaximal Ca2+-activated tension. The areas of the tension transients were unchanged when cAMP was present in the releasing solution (release phase), and were significantly increased up to a mean of about 80% when cAMP or PK-C was present in the Ca2+ loading solutions (uptake phase). The increased tension transient was blocked by the heat-stable inhibitor of cAMP kinase. We conclude that cAMP-induced increases in Ca2+ uptake by the SR could play an important role in the positive inotropic effect. cAMP kinase could thus play a crucial role in the regulation of myocardial contractility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01108307
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  • 9
    Electronic Resource
    Electronic Resource
    Effects of halothane on caffeine-induced tension transients in functionally skinned myocardial fibers (1979)
    Springer
    Pflügers Archiv 380 (1979), S. 29-34 
    Details
    ISSN: 1432-2013
    Keywords: Cardiac muscle ; Skinned fibers ; Halothane ; Sarcoplasmic reticulum ; Caffeine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of halothane on caffeine-induced tension transients in functionally skinned myocardial fibers were investigated. Fiber bundles from mechanically disrupted rabbit right ventricular papillary muscles were mounted on a tension transducer. The fiber preparation was loaded with Ca2+; Ca2+ was then released by the use of caffeine (25 mM); and the area of the resulting tension transient was measured. Each preparation was sequentially transferred from control to test to control solution. The control solutions were equilibrated with 100% N2, and the test solutions with a mixture of N2 and various halothane concentrations. The preparation was exposed to halothane during the Ca2+ uptake or the release phase only, or during both Ca2+ uptake and release phases. The areas of the test tension transients were compared with those of the two control tension transients. It was found that halothane depressed the caffeine-induced tension transient either during the uptake phase or the combined-uptake-and-release phase but not during the release phase. The halothane-induced depression was dose-dependent, reversible, and comparable to the depression observed in intact isolated papillary muscles. We conclude that halothane could induce myocardial depression by inhibiting Ca2+ uptake by the sarcoplasmic reticulum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00582608
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  • 10
    Electronic Resource
    Electronic Resource
    Effects of ryanodine on skinned skeletal muscle fibers of the rabbit (1987)
    Springer
    Pflügers Archiv 410 (1987), S. 510-516 
    Details
    ISSN: 1432-2013
    Keywords: Ryanodine ; Skinned muscle fiber ; Soleus ; Adductor Magnus ; Contractile proteins ; Sarcoplasmic reticulum ; Calcium ; Caffeine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The mechanism(s) of ryanodine-induced contracture of skeletal muscle were studied in skinned fibers from soleus (SL) and adductor magnus (AM) (slow- and fast-twitch skeletal muscles) of rabbits. Pieces of SL or AM were homogenized (sarcolemma disrupted). Single fibers were dissected from the homogenate and mounted on photodiode force transducers. At concentrations 1–50 μM, ryanodine slightly but significantly increased the submaximal Ca2+-activated tension development of the contractile proteins in skinned fibers of AM but not of SL. Ryanodine in uptake phase or release phase increased caffeine-induced tension transients in the SR of both muscle types; however, no dose-response relation was found. Ryanodine ≥1 μM decreased, however, the second control tension transients in a dose-dependent manner. The depression was nearly irreversible and “activity”-dependent. The concentrations of ryanodine that inhibited the second control tension transients by 50% were 10 μM and 5 μM for SL and AM, respectively, following ryanodine administration in the release phase, and 100 μM and 30 μM, respectively, for these preparations after the drug was present in the uptake phase. The quantity of calcium released from the SR by Triton X-100 and caffeine in the second control tension transient was unchanged by ryanodine at all concentrations tested when compared with that of the absence of ryanodine. The present findings suggest that the ability of ryanodine to increase immediate calcium release from the SR, and in AM but not SL, to increase the sensitivity of the contractile proteins to Ca2+ underlies the contracture caused by this agent in intact skeletal muscles. The delayed decreased Ca2+ efflux by caffeine, as evidenced by depression of tension transient with no change in the calcium content may be responsible for the decreased twitch tension caused by this agent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00586534
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