Sarcomere length effects on the Sr2+- and Ca2+-activation curves in skinned frog muscle fibres

Moisescu, D. G.; Thieleczek, Rolf

doi:10.1016/0005-2728(79)90170-1

Cited by 66 publications

(40 citation statements)

References 12 publications

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“…This procedure was modified because we observed that shortening of the sarcomeres often occurred during the first full tension. Left shifts of -0.1 p units have been reported for fibers stretched above slack length (Fabiato and Fabiato, 1978 ;Moisescu and Thieleczek, 1979) .…”

Section: Discussionmentioning

confidence: 89%

Effect of cross-bridge kinetics on apparent Ca2+ sensitivity.

Brandt¹,

Cox²,

Kawai³

et al. 1982

The Journal of General Physiology

148

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Three different ways of shifting the pCa/tension curve on the pCa axis have been studied and related to changes in the rate constants of the crossbridge cycle. The curve midpoint shifts to higher pCa's wheel the substrate (Mg-ATP) is reduced from 5 to 0.25 mM, when the phosphate concentration is reduced from 7.5 mM to 0, and when the ionic strength is reduced from 0.200 to 0.120 . The Hill coefficients of the pCa/tension curve in our standard saline (5 mM substrate, 5 mM free ATP, 7.5 mM phosphate, ionic strength 0.200, 15°C) are between 5.1 and 5.6 and fall to 3.0 with the left shift of the curve brought about by reducing both substrate and phosphate. Left shifts of the curve produced by reduction in the ionic strength do not result in a lower Hill coefficient . Reducing either substrate or phosphate is associated with a reduction in the optimal frequency for oscillatory work, but reduction in ionic strength is not so associated . Maximum tension increases with the left shift of the curve brought about by reducing phosphate concentration or ionic strength, but tension decreases with the left shift of the curve accompanying substrate concentration reduction in a phosphate-free saline . We argue that one mechanism for the observed shift of the curve along the pCa axis is the relationship between the time a cross-bridge takes to complete a cycle and the time Ca 2+ stays bound to troponin C (TnC) . If the cycle rate is decreased, a smaller fraction of TnC sites must be occupied to keep a given fraction of cross-bridges active . To illustrate this concept, we present a simplified model of the cross-bridge cycle incorporating the kinetics of Ca binding to TnC.

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Section: Discussionmentioning

confidence: 89%

Effect of cross-bridge kinetics on apparent Ca2+ sensitivity.

Brandt¹,

Cox²,

Kawai³

et al. 1982

The Journal of General Physiology

148

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“…The composition of all the solutions was calculated by the Fabiato computer program (Fabiato, 1988). The program calculation was used with stability constants listed for Ca 2+ (Orentlicher et al, 1977) and for Sr 2+ (Moisescu & Thieleczek, 1979), to keep ®nal ionic strength at 200 mM. pH was adjusted to 7.0 and ATP at 2.5 mM was added to each solution, except extraction solution.…”

Section: Solutionsmentioning

confidence: 99%

The role of the Ca²⁺ regulatory sites of skeletal troponin C in modulating muscle fibre reactivity to the Ca²⁺ sensitizer bepridil

Kischel¹,

Bastide²,

Potter

et al. 2000

British J Pharmacology

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1 The Ca 2+ -sensor protein troponin C (TnC) exerts a key role in the regulation of muscle contraction, and constitutes a target for Ca 2+ sensitizer compounds, such as bepridil, known to increase its apparent Ca 2+ a nity. Moreover, bepridil has been reported to exert a di erential e ect in slow and fast skeletal muscle ®bres, which express the slow/cardiac and fast TnC isoform, respectively. 2 The role of the TnC isoform in establishing the di erential e ect of bepridil was assessed in slow soleus and fast tibialis rat skinned ®bres, by extraction of endogenous TnC and consecutive reconstitution with either slow or fast recombinant TnC. A mutant (VG2), lacking the regulatory site II, was also used to distinguish the role of each regulatory site. 3 Fast tibialis ®bres reconstituted with cardiac TnC exhibited a typical slow bepridil reactivity, while slow soleus ®bres reincorporated with fast TnC displayed a typically fast reactivity to bepridil. These results indicated that the di erential e ect of bepridil in slow and fast ®bres is related to the TnC isoform predominantly expressed in a ®bre. 4 Experiments with the VG2 mutant demonstrated that BPD can achieve an increase in the Ca 2+ a nity in the absence of a functional site II. Thus, site I was necessary for the BPD e ect to be independent of the Ca 2+ concentration. Moreover, the amplitude of the reinforcement in the Ca 2+ a nity, induced by the binding of bepridil to the TnC molecule, is dependent on the number of functional regulatory sites, the larger a nity reinforcement being detected when only one regulatory site (either site I or II) is functional.

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“…In Table 2 are listed the values for the apparent affinity constants which were required for this study. These values were either determined by us for our conditions using potentiometric methods similar to those described earlier (Moisescu & Thieleczek, 1978Stephenson & Williams, 1981Thieleezek, 1982, or were calculated according to Sillen & Martell (1964, 1970 (Moisescu & Thieleczek, 1979 (I, up to 285 mM) and Cl-concentration (up to 40 mM) compared with the normal activation solutions (I = 250 mm, Cl-concentration = 20 mM), because the Ba2+ levels were higher. A BaATP precipitate appeared in the solutions at free Ba2+ concentrations corresponding to more than 90 % of the maximum isometric tension.…”

Section: Solutionmentioning

confidence: 99%

Activation of the contractile apparatus of skinned fibres of frog by the divalent cations barium, cadmium and nickel.

Stephenson¹,

Thieleczek²

1986

The Journal of Physiology

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SUMMARY1. The contractile apparatus of mechanically skinned muscle fibres of frog can be reversibly activated by Ba2+ and Cd2 .2. The maximum force induced by both Ba2+ and Cd2+ is the same as that induced by Ca2+ and Sr2+.3. The ionic concentrations of the divalent cations required to induce 50 % of the maximum activated force at 1 mM-Mg2+, pH 7410, 22 TC and 250 mm ionic strength are about 8 x 10-7 M for Ca2+, 5 X 10-6 M for Cd2+, 2-6 x 10-5 M for Sr2+ and 7 x 10-4 M for Ba2+.4. Exposure of the skinned fibre to relatively low Ni2+ concentrations (between 10-6 and 10-5 M) resulted in a transient force response accompanied by an irreversible change in the ability of the preparation to develop force.5. The Ba2+-and Cd2+-activation curves are considerably flatter than the corresponding curves for Ca2+ and Sr2+.6. An increase in Mg2+ concentration from 1 to 3 mm decreased the sensitivity of the contractile apparatus to Ba2+ by a factor of about 1P5 without affecting the maximum force response.7. The Ca2+-activation curve was modified in the presence of subthreshold concentrations of Ba2+ and the results indicate that Ba2+ could have both an activating and an inhibitory action on the Ca2+-activated force.8. A kinetic model which can quantitatively explain the results for activation of contraction by Ba2+ and Ca2+, is described.

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Sarcomere length effects on the Sr2+- and Ca2+-activation curves in skinned frog muscle fibres

Cited by 66 publications

References 12 publications

Effect of cross-bridge kinetics on apparent Ca2+ sensitivity.

Effect of cross-bridge kinetics on apparent Ca2+ sensitivity.

The role of the Ca²⁺ regulatory sites of skeletal troponin C in modulating muscle fibre reactivity to the Ca²⁺ sensitizer bepridil

Activation of the contractile apparatus of skinned fibres of frog by the divalent cations barium, cadmium and nickel.

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Sarcomere length effects on the Sr2+- and Ca2+-activation curves in skinned frog muscle fibres

Cited by 66 publications

References 12 publications

Effect of cross-bridge kinetics on apparent Ca2+ sensitivity.

Effect of cross-bridge kinetics on apparent Ca2+ sensitivity.

The role of the Ca2+ regulatory sites of skeletal troponin C in modulating muscle fibre reactivity to the Ca2+ sensitizer bepridil

Activation of the contractile apparatus of skinned fibres of frog by the divalent cations barium, cadmium and nickel.

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The role of the Ca²⁺ regulatory sites of skeletal troponin C in modulating muscle fibre reactivity to the Ca²⁺ sensitizer bepridil