Calcium content and exchange in frog skeletal muscle.

Kirby, Albert C.; Lindley, Barry D.; Picken, John R.

doi:10.1113/jphysiol.1975.sp011178

Cited by 28 publications

(16 citation statements)

References 14 publications

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“…Our results suggest that 45 Ca, identified in radioautographs as bound to LSR (108,109), was in fact bound to Ca-binding proteins . The combined results of the analysis ofthe TC and of the LSR are also inconsistent with the interpretation of Ca" flux data that ascribe a relatively small (0.2 mmol/kg wet muscle), fast exchanging (time constant = 2.7 min) component as representing the Ca content of the TC, and a larger (0.54 mmole/kg wet muscle) slowly exchanging (time-constant = 1,244 min) component to the LSR (54). The relatively low Ca content of the LSR that, in contrast to the TIC, contains little or no calsequestrin (12,51,52,66), does support the conclusion that the free Ca" in the SR is in the low millimolar range (104).…”

Section: The Composition Of the Cytoplasm And Of The Lsr During Tetancontrasting

confidence: 72%

Calcium release and ionic changes in the sarcoplasmic reticulum of tetanized muscle: an electron-probe study.

Somlyo¹,

González‐Serratos²,

Shuman³

et al. 1981

The Journal of Cell Biology

421

223

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Approximately 60-70% of the total fiber calcium was localized in the terminal cisternae (TC) in resting frog muscle as determined by electron-probe analysis of ultrathin cryosections . During a 1 .2 s tetanus, 59% (69 mmol/kg dry TC) of the calcium content of the TC was released, enough to raise total cytoplasmic calcium concentration by -1 mM . This is equivalent to the concentration of binding sites on the calcium-binding proteins (troponin and parvalbumin) in frog muscle . Calcium release was associated with a significant uptake of magnesium and potassium into the TC, but the amount of calcium released exceeded the total measured cation accumulation by 62 mEq/kg dry weight . It is suggested that most of the charge deficit is apparent, and charge compensation is achieved by movement of protons into the sarcoplasmic reticulum (SR) and/or by the movement of organic co-or counterions not measured by energy dispersive electron-probe analysis . There was no significant change in the sodium or chlorine content of the TIC during tetanus. The unchanged distribution of a permeant anion, chloride, argues against the existence of a large and sustained transSR potential during tetanus, if the chloride permeability of the in situ SR is as high as suggested by measurements on fractionated SR .The calcium content of the longitudinal SR (LSR) during tetanus did not show the LSR to be a major site of calcium storage and delayed return to the TC . The potassium concentration in the LSR was not significantly different from the adjacent cytoplasmic concentration. Analysis of small areas of I-band and large areas, including several sarcomeres, suggested that chloride is anisotropically distributed, with some of it probably bound to myosin . In contrast, the distribution of potassium in the fiber cytoplasm followed the water distribution . The mitochondrial concentration of calcium was low and did not change significantly during a tetanus. The TIC of both tetanized and resting freeze-substituted muscles contained electron-lucent circular areas . The appearance of the TIC showed no evidence of major volume changes during tetanus, in agreement with the estimates of unchanged (-72%) water content of the TIC obtained with electron-probe analysis .The release of Ca from and its subsequent return to the triadic portion of the sarcoplasmic reticulum (SR) (28,80,82) are the major determinants of the contractile cycle of striated muscle (for review, see reference 24) . Since the demonstration of the SR as the ATP-dependent relaxing factor (57), a wealth of information has been accumulated about the kinetics and THE JOURNAL OF CELL BIOLOGY " VOLUME 90 SEPTEMBER 1981 577-594 © The Rockefeller University Press -0021-9525/81/09/0577/18 $1 .00 mechanisms of calcium uptake by the SR (e.g., 41,48,63,104,106, and for review, see references 62, 102). In contrast, comparatively little is known about the mechanism of release and associated ion movements, largely because isolated SR preparations do not lend themselves to reproduction of the ph...

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Section: The Composition Of the Cytoplasm And Of The Lsr During Tetancontrasting

confidence: 72%

Calcium release and ionic changes in the sarcoplasmic reticulum of tetanized muscle: an electron-probe study.

Somlyo¹,

González‐Serratos²,

Shuman³

et al. 1981

The Journal of Cell Biology

421

223

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“…Whether the increase is due to a Ca binding protein similar to that of the intestinal mucosa (see Introduction) must await further investigation. Extracellular bound Ca has been observed in many other tissues including smooth muscle (Weiss & Goodman, 1969), skeletal muscle (Kirby, Lindley & Picken, 1975), anterior pituitary slices (Moriarity, 1980) and barnacle muscle fibres (Bacigalupo, Luxoro, Rissetti & Vergara, 1979).…”

Section: Discussionmentioning

confidence: 99%

Calcium fluxes in mouse mammary tissue in vitro: intracellular and extracellular calcium pools

Neville

Peaker

1982

The Journal of Physiology

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SUMMARY1. The total Ca content of the mammary gland increased from about 2 to 12 #smole/g tissue during the transition from pregnancy to lactation in the mouse.In tissue from lactating mice at least two thirds of the total Ca exchanged with external Ca in 6 hr. There was little non-exchangeable Ca in tissues from pregnant mice.2. At 37 'C the time courses of influx and efflux of 45Ca in lactating tissues could be analysed by assuming three exponential components with rate constants of about 03, 006 and 0005 min-and containing, respectively, 1-7, 1-5 and 4-7 mole 45Ca/g tissue at the steady state.3. The rapidly effluxing component showed the time-and temperature-dependence characteristic of bulk-phase-limited diffusion through the extracellular space. The diffusion coefficient was about one quarter of the self-diffusion coefficient of Ca in aqueous solution, consistent with a tortuosity factor of about 2. A portion of the Ca in this component was displaced by La3+. The amount remaining in the presence of 3 mM-La3+ was close to that expected for free extracellular Ca. The rapid component was therefore interpreted as originating from an extracellular compartment containing both free and bound Ca.4. The rate of efflux of the intermediate component was slowed by a factor of ten when the temperature was decreased from 37 to 0C giving a Q10 of 2-7, expected for membrane transport. The slow component present at 37 'C was not displaced by EGTA or La3+, suggesting that it is not localized extracellularly. It was not apparent in the 0 'C efflux curves. 5. The biphasic time course of uptake of ionophore (A23187)-releasable 45Ca in particulate fractions obtained by homogenization and centrifugation of tissues which had been incubated with the isotope was consistent with the hypothesis that the two slower components of 45Ca flux originate from intracellular compartments. Mitochondrial uptake probably did not contribute significantly to Ca exchange in these tissues.6. 45Calcium fluxes in mammary tissues from pregnant mice also showed three

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“…There is much evidence that terminal cisternae and longitudinal SR of frog twitch muscle are separated by a diffusion barrier: (a) Winegrad (1968), using autoradiographic techniques, found that calcium movements from longitudinal tubules to terminal cisternae can take more than 20 s after a tetanus, suggesting a diffusion barrier between those structures. (b) Kirby et al (1975), using tracer experiments on single muscle fibers and small muscles, conclude that calcium washes out of the terminal cisternae with a time constant of 2.7 min, whereas it washes out of the longitudinal SR with a time constant of 1,244 min. Winegrad (1970) also found that calcium in the terminal cisternae exchanges with the external medium much more quickly than calcium in the SR.…”

Section: Evaluation Of Modelsmentioning

confidence: 99%

Electrical models of excitation-contraction coupling and charge movement in skeletal muscle.

Mathias¹,

Levis²,

Eisenberg³

1980

The Journal of General Physiology

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A B ST R A C T The consequences of ionic current flow from the T system to the sarcoplasmic reticulum (SR) of skeletal muscle are examined. The Appendix analyzes a simple model in which the conductance gx, linking T system and SR, is in series with a parallel resistor and capacitor having fixed values. The conductance gx is supposed to increase rapidly with depolarization and to decrease slowly with repolarization. Nonlinear transient currents computed from this model have some of the properties of gating currents produced by intramembrane charge movement. In particular, the integral of the transient current upon depolarization approximates that upon repolarization. Thus, equality of nonlinear charge movement can occur without intramembrane charge movement. A more complicated model is used in the text to fit the structure of skeletal muscle and other properties of its charge movement. Rectification is introduced into gx and the membrane conductance of the terminal cisternae to give asymmetry in the time-course of the transient currents and saturation in the curve relating charge movement to depolarization, respectively. The more complex model fits experimental data quite well if the longitudinal tubules of the sarcoplasmic reticulum are isolated from the terminal cisternae by a substantial resistance and if calcium release from the terminal cisternae is, for the most part, electrically silent. Specific experimental tests of the model are proposed, and the implications for excitation-contraction coupling are discussed.

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Calcium content and exchange in frog skeletal muscle.

Cited by 28 publications

References 14 publications

Calcium release and ionic changes in the sarcoplasmic reticulum of tetanized muscle: an electron-probe study.

Calcium release and ionic changes in the sarcoplasmic reticulum of tetanized muscle: an electron-probe study.

Calcium fluxes in mouse mammary tissue in vitro: intracellular and extracellular calcium pools

Electrical models of excitation-contraction coupling and charge movement in skeletal muscle.

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