<i>In vitro</i> Studies of the Gain and Exchange of Calcium in Frog Skeletal Muscle

Cosmos, Ethel; Harris, E. J.

doi:10.1085/jgp.44.6.1121

Cited by 62 publications

(18 citation statements)

References 7 publications

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“…Taken together, these observations suggest that the mechanical potentiation caused by Na § deprivation is correlated with an increase in myoplasmic Ca 2+. In agreement with this interpretation, it has been reported that low [Na+]o increases the content of calcium in frog muscle (Cosmos & Harris, 1961). An increase in intracellular calcium would favour calcium release by SR through a calcium-induced-calcium release mechanism.…”

Section: Sodium Ions and Contractionsupporting

confidence: 74%

Effect of sodium deprivation on contraction and charge movement in frog skeletal muscle fibres

García¹,

Díaz

Godı́nez

et al. 1992

J Muscle Res Cell Motil

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Measurements of isometric tension were performed in single twitch skeletal muscle fibres and the effect of extracellular Na+ removal on contraction was investigated. Na+ withdrawal brought about an increase in the amplitude of K+ contractures and their time course became faster. The potentiation of K+ contractures depended strongly on extracellular Ca2+ and developed slowly following an exponential time course with a time constant of approximately 8 min. Removal of extracellular Na+ greatly increased the amplitude of caffeine contractures and lowered its threshold: caffeine (0.5 mM) had no effect on resting tension in Ringer's but produced contractures in Na(+)-free solutions. Intramembrane charge movement (charge 1) was monitored in contracting voltage-clamped segments of frog skeletal muscle fibres using the triple-Vaseline-gap technique. Movement of charge 1 did not depend on the presence of extracellular Na+. However, the mechanical threshold decreased by approximately 10 mV at several pulse durations and the charge which produced just detectable contractions decreased by approximately 5 nC microF-1 in the absence of extracellular Na+. Intracellular heparin (40 mg ml-1) increased the mechanical threshold by approximately 20 mV without affecting the movement of charge 1. The effect of Na(+)-free solutions on the mechanical threshold was additive to that of heparin. It is concluded that the effects of Na(+)-withdrawal on contraction take place at a location beyond the voltage sensor of excitation-contraction coupling.

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Section: Sodium Ions and Contractionsupporting

confidence: 74%

Effect of sodium deprivation on contraction and charge movement in frog skeletal muscle fibres

García¹,

Díaz

Godı́nez

et al. 1992

J Muscle Res Cell Motil

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“…Although the efflux of Ca across the surface membrane therefore represents only a small fraction of the Ca changes occurring within the fibre during a response, it was of interest to examine the processes that determine the transport of this divalent ion and in particular whether Ca and Mg share the same transport system in this preparation (see Ashley & Ellory, 1972). There are at least two different Ca pumps which operate in cells; an ATP Ca MOVEMENTS IN SINGLE MUSCLE FIBRES requiring, Na-independent system is found in red cells (Schatzmann, 1966), the membranes of the sarcoplasmic reticulum (Ebashi & Lipmann, 1962;Hasselbach & Makinose, 1961 and in some other preparations, such as L cells (Lamb & Lindsay, 1971): while in excitable tissues, such as nerve (Baker, 1972), synaptosomes (Blaustein & Wiesmann, 1970), heart muscle (Reuter & Seitz, 1968) and skeletal muscle (Cosmos & Harris, 1961;Baker, 1972;Dipolo, 1973), the transport of Ca depends mainly upon the downhill movement of Na ions. It is difficult to investigate the ATP-dependence of the Ca transporting system in muscle since highenergy phosphate compounds are required to maintain the Ca stores within the sarcoplasmic reticulum and even in dialysed barnacle muscle fibres, there is still sufficient ATP present to activate completely the Na pump (Dipolo, 1973).…”

Section: Discussionmentioning

confidence: 99%

Calcium movements in single crustacean muscle fibres

Ashley¹,

Ellory²,

Hainaut³

1974

The Journal of Physiology

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1. Internal microinjection of the Ca‐sensitive photoprotein aequorin or the isotope 45Ca have been used to assess Ca movements in single muscle fibres from the barnacle Balanus nubilus and the crab Maia squinado. 2. Progressive isosomotic replacement of external Na by Li, choline, sucrose or Tris was associated with a rapid increase in the level of light emission from internally injected aequorin. This response was dependent upon the presence of external Ca. The light output was maximal for Na concentrations < 50 m M in the replaced salines, while Na concentrations > 350 m M produced no apparent increase in the resting light emission. 3. If the Ca concentration in the external saline was altered, no effect was observed in Na replaced salines when the Ca concentration was < 1 m M, but maximal effects were observed at concentrations of Ca of ca. 100 m M. 4. The increased light emission from aequorin in Na‐replaced salines was substantially inhibited by 1 m M‐La3+ applied externally, but not by N‐ethyl maleimide (NEM), propanolol or D‐600. 5. Following microinjection of 45Ca and 2 hr equilibration, the residual efflux of Ca was shown to be sensitive to the removal of external Ca and Na, the extent of each component being variable. 6. The Na‐sensitive Ca efflux was partially inhibited by external La3+ (1 m M), but not by high concentrations of Mg2+, Ca2+, Mn2+ or Co2+. It was stimulated by NEM and ethacrynic acid, which was considered to be due to an indirect effect upon the sarcoplasmic reticulum. 7. It is concluded that Ca movements in these single crustacean muscle fibres involve Na gradients and a Ca: Ca exchange and from the relative insensitivity of Ca movements to various inhibitors, in contrast to the Mg system, it seems that there may be two independent modes for divalent cation transport in this preparation.

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“…Lolley's result (57) showed that the calcium and sodium contents of the incubated tissue were dependent on the concentration of calcium in the outer fluid, but even when the sodium content of the tissue increased due to stimulation, the calcium content of the tissue did not follow this increase but showed no change, or rather had a tendency to decrease. The existence of calcium transport has been evidenced (57,58) and, in muscle and liver with medium low in sodium, it seems that calcium is taken up from the medium (58,59). Judah et al (58) concluded, by ob serving the extrusion of calcium from the liver slices being greatly reduced by the low external sodium, that calcium transport was dependent upon a normal sodium transport and calcium competed with sodium for the transport site.…”

Section: Besides Itmentioning

confidence: 99%