Model for the Action of Calcium in Muscle

Ashley, Christopher; Moisescu, D. G.

doi:10.1038/newbio237208a0

Cited by 60 publications

(50 citation statements)

References 21 publications

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“…The results are in better agreement with the 'consecutive' scheme of reaction rather than with the 'independent' alternative (Ashley & Moisescu, 1972) for the co-operative action of two Ca2+ ions in the process of tension activation in crustacean skeletal muscle.…”

Section: Discussionsupporting

confidence: 77%

“…Varying the K+ concentration in the activating solutions was also INTRODUCTION One way to examine the influence of Ca2+ ions upon the properties of the contractile machinery is to employ large single muscle fibres which have been micro-injected with a Ca2+-sensitive photoprotein such as aequorin, and to examine the simultaneous emission of light and mechanical response upon activation (Ashley & Ridgway, 1970;Ashley & Moisescu, 1972). Another method is to by-pass the membrane depolarization step of excitation-contraction coupling, and activate isolated bundles of myofibrils directly (Natori, 1954) in Ca2+-buffered solutions (Hellam & Podolsky, 1969).…”

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confidence: 99%

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Effect of changing the composition of the bathing solution upon the isometric tension—pCa relationship in bundles of crustacean myofibrils

Ashley¹,

Moisescu²

1977

The Journal of Physiology

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170

123

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SUMMARY1. The relative isometric tension-pCa relationship has been determined for isolated bundles of barnacle myofibrils under a variety of ionic conditions using [Ca2+]-buffered solutions which also contained an ATP regenerating system (creatine phosphate and creatine kinase).2. The results are in better agreement with the 'consecutive' scheme of reaction rather than with the 'independent' alternative (Ashley & Moisescu, 1972) for the co-operative action of two Ca2+ ions in the process of tension activation in crustacean skeletal muscle.3. Variations in the pH of the activating solutions did have a marked effect on the relative tension-pCa curve, although no effect was observed on the absolute maximum value for isometric tension. A shift in pH by 0-5 u. in the range 6-6-7-6 shifted the Ca2+-activation curve by 0.5 log u. towards lower free Ca2+ concentrations.4. Changes in the free Mg2+ concentration of the activating solutions in the millimolar range produced a pronounced shift of the relative tension-pCa curve along the pCa axis. Increasing [Mg2+] from 1 to 5 mM shifted the curve by about 0-7 log u. to higher free Ca2+ concentrations, without significantly modifying its steepness.5. Changes in the MgATP concentration of the activating solutions in the range of 1-13 mm had no significant effect on the relative tension-pCa relationship.6. Varying the K+ concentration in the activating solutions was also

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Section: Discussionsupporting

confidence: 77%

mentioning

confidence: 99%

Effect of changing the composition of the bathing solution upon the isometric tension—pCa relationship in bundles of crustacean myofibrils

Ashley¹,

Moisescu²

1977

The Journal of Physiology

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170

123

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“…Fast force activation of skinnedmuscle fibres in Ca2+-and Sr2+-bufferedsolutions It has been predicted (Ashley & Moisescu, 1972) and it has been recently demonstrated (Moisescu, 1976a) that the rate of tension development is strongly dependent upon the free Ca concentration in the activating solutions, under otherwise constant conditions. In this context we were interested to see if with the method described in this paper is possible to activate the frog myofibrillar preparation with rate constants approaching the values observed in vivo for tetanic stimulation.…”

Section: J0*1 Pomentioning

confidence: 99%

Calcium and strontium concentration changes within skinned muscle preparations following a change in the external bathing solution.

Moisescu¹,

Thieleczek²

1978

The Journal of Physiology

210

130

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1. A method for producing rapid [Ca2+] and [Sr2+] changes in the frog skinned muscle fibre preparation while maintaining constant all other cationic concentrations (Moisescu, 1976a, b) is described and analysed in detail. 2. Different experiments, some of them involving the Ca2+‐sensitive photoprotein aequorin, as well as theoretical considerations, indicate that with this method one can produce a Ca2+ (or Sr2+) concentration change within 0.1‐‐0.15 sec in a whole preparation having a diameter of 50 micrometer. 3. The rate of force development was similar to that observed in vivo. 4. The radial diffusion coefficient of EGTA in relaxed myofibrillar preparations was measured and found to be 4.6 x 10(‐6) cm2sec‐1 at 20 degrees C. 5. The sarcoplasmic reticulum in myofibrillar bundles was found to be active with respect to both Ca2+ and Sr2+ in the solutions used ([Mg2+] 1 mM; [Na] 30 mM; [K] 140‐170 mM; [Cl] less than or equal to 20 mM; pH 7.10). 6. The amount of Ca released by caffeine from internal stores (previously loaded with Ca) can raise the total Ca concentration in the muscle fibre preparation by at least 1.8 mM. 7. The presence of 10 mM‐caffeine in all bathing solutions reduced drastically the ability of the sarcoplasmic reticulum to accumulate both Ca and Sr.

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“…2B and 3B). In calculating model curves for comparison with data, many investigators (25,26) have assumed that the activations are proportional, or nearly so (8), to the extent of occupation of appropriate Ca2O sites. This assumption is not born out in Figs.…”

Section: The Modelmentioning

confidence: 99%

Activation of thin-filament-regulated muscle by calcium ion: considerations based on nearest-neighbor lattice statistics.

Shiner¹,

Solaro

1982

Proc. Natl. Acad. Sci. U.S.A.

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We discuss the activation of thin-filament-regulated muscles by calcium ion in terms of a qualitative model based on nearest-neighbor lattice statistics. For the most part, the model takes into account only the essential features of the phenomenon-that there must be an interaction between calcium adsorption to troponin and crossbridge reaction with actin for calcium ion to activate contraction and that the relevant stationary states are nonequilibrium ones. Even so, the model predicts the following features which are seen experimentally but have generally not been considered in previous models: (i) the relative activations of stationary-state isometric force and ATPase are not equal; (ii) in general, neither activation of force nor that of ATPase is proportional to calcium adsorption to the activating sites; and (iii) the slopes of the relations between the activations and the logarithm of the calcium ion concentration generally depend on the necessary interaction between calcium ion adsorption and crossbridge reaction with actin. Thus, these relations show cooperative effects even if there is no interaction between calcium adsorption sites.There is significant understanding ofthe relations between the molecular events and their phenomenological manifestations in the activation of muscle contraction by calcium ion (1-4). Yet this understanding is not complete. Much of it is based on concepts from the theory of equilibrium systems and from other limiting cases, whereas contraction and its activation are distinctly nonequilibrium phenomena, even at the stationary state, and the limiting cases are so particular that they would not seem to obtain in muscle. We have recently begun to develop a model of cooperative systems with nonequilibrium stationary states (5), and in this paper we use this model to offer insights into these facets of the Ca2" activation process. We will attempt to show that some of the previous interpretations of this process have been based on untenable assumptions. We will also offer explanations for some puzzling aspects ofthe phenomenon, but we will not attempt to develop a complete quantitative model; our goal is qualitative rather then quantitative. We will consider only essential aspects of the phenomenon so that the model reflects its basic features. (Derivations of the approximations and details of other points are available upon request.) The model should thus be considered a paradigm for more accurate models. THE MODELWe picture the thin filament as a lattice of two classes of sites: those on troponin that adsorb Ca2" and the actins. Contraction is brought about by a cyclic reaction of projections of myosin from the thick filament, the crossbridges, with the actins and is powered by an ATPase located on the myosins (1-4). It is generally acknowledged that a crossbridge may exist in various states, both when it is reacting with an actin and when it is not reacting. However, because we are concerned with the activation of contraction, not the contraction itself, a two-state cros...

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Model for the Action of Calcium in Muscle

Cited by 60 publications

References 21 publications

Effect of changing the composition of the bathing solution upon the isometric tension—pCa relationship in bundles of crustacean myofibrils

Effect of changing the composition of the bathing solution upon the isometric tension—pCa relationship in bundles of crustacean myofibrils

Calcium and strontium concentration changes within skinned muscle preparations following a change in the external bathing solution.

Activation of thin-filament-regulated muscle by calcium ion: considerations based on nearest-neighbor lattice statistics.

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