T‐tubule swelling in hypertonic solutions: a freeze substitution study.

Franzini-Armstrong, C; Heuser, John E.; Reese, Thomas S.; Somlyo, A.P.; Somlyo, A V

doi:10.1113/jphysiol.1978.sp012492

Cited by 53 publications

(35 citation statements)

References 35 publications

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“…Almers et al (1981), using a more complete modelling, found that for frog muscle the volume of the fibre depleted of Ca was about 0-004 of the fibre volume, similar to the volume enclosed by the T-system (Peachey, 1965). In insect muscle fibres, the volume of the T-system may be somewhat greater since membrane capacity is higher than in frog muscle fibres of comparable diameter , and in the hypertonic solutions we use, the T-system is probably swollen (see Franzini-Armstrong, Heuser, Reese, Somlyo & Somlyo, 1978).…”

Section: Depletion May Contribute To Inactivation In Ba Solutionsmentioning

confidence: 74%

Calcium inactivation in skeletal muscle fibres of the stick insect, Carausius morosus.

Ashcroft¹,

Stanfield²

1982

The Journal of Physiology

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SUMMARY1. Inactivation of Ca currents in skeletal muscle fibres of the stick insect, Carausius morosus, was studied using a three-electrode voltage-clamp method.2. The extent of inactivation showed a voltage-dependence similar to that of the Ca current, inactivation being absent in the absence of a Ca current, maximal at potentials where Ca currents are largest, and reduced at potentials close to Eca.3. Ca currents inactivated along a double exponential time course, both when measured from the decline ofCa current during a single pulse and when measured using a two pulse protocol. In 20 mM-Ca-Ringer the fast time constant of inactivation had a mean value of 27 msec and that of the slow time constant was 134 msec, at 0 mV and 5 'C.4. The rate of inactivation was slowed, and its extent reduced, in low [Ca]0, where Ca currents are smaller. Similarly, inactivation was faster and more complete in highCa-Ringer.5. The rate of recovery from inactivation also followed a double exponential time course, with time constants of 638 msec and 4 see following a 500 msec inactivating pulse in 20 mM-Ca-Ringer at 5 'C. Recovery appeared to be related to the amount of Ca entry during the inactivating pulse, being slower in high [Ca]. and following longer inactivating pulses.6. Inactivation was slowed and reduced in extent when Ba2+ or Sr2+ carried current. Inactivation in Ba solutions may be due to depletion of Ba2+ from the lumen of the transverse tubules.7. Ba2+ does not compete with Ca2+ for the inactivation mechanism. 8. It is concluded that inactivation of Ca currents in stick insect muscle fibres is primarily mediated by Ca2+ entry.

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Section: Depletion May Contribute To Inactivation In Ba Solutionsmentioning

confidence: 74%

Calcium inactivation in skeletal muscle fibres of the stick insect, Carausius morosus.

Ashcroft¹,

Stanfield²

1982

The Journal of Physiology

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“…In intact muscle fibers, the transverse tubule component of the triad selectively swells by simple replacement of the external medium with hypertonic solutions of either sucrose or salt (47). The added solutes enter the t-system via the transverse tubule "mouth" or caveolae, causing an osmotic imbalance between the cytoplasmic compartment and lumen of the tubule.…”

Section: Susceptibility Of Triad Morphology To Salt Treatment or Osmomentioning

confidence: 99%

Morphology of isolated triads.

Mitchell¹,

Saito²,

Palade³

et al. 1983

The Journal of Cell Biology

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The triad is the junctional association of transverse tubule with sarcoplasmic reticulum terminal cisternae. A procedure for the isolation of highly enriched triads from skeletal muscle has been described in the previous paper. In the present study, the structural features of isolated triads have been examined by thin-section, negative-staining, and freezefracture electron microscopy. In isolated triads, key features of the structure observed in situ have been retained, including the osmiophilic "feet," junctional structures between the transverse tubule and terminal cisternae. New insight into triad structure is obtained by negative staining, which also enables visualization of feet at the junctional face of the terminal cisternae, whereas smaller surface particles, characteristic of calcium pump protein, are not visualized there. Therefore, the junctional face is different from the remainder of the sarcoplasmic reticulum membrane. Junctional feet as viewed by thin section or negative staining have similar periodicity and extend -100 ,~ from the surface of the membrane. Freeze-fracture of isolated triads reveals blocklike structures associated with the membrane of the terminal cisternae at the junctional face, interjunctional connections between the terminal cisternae and t-tubule, and intragap particles. The intragap particles can be observed to be closely associated with the t-tubule. The structure of isolated triads is susceptible to osmotic and salt perturbation, and examples are given regarding differential effects on transverse tubules and terminal cisternae. Conditions that adversely affect morphology must be considered in experimentation with triads as well as in their preparation and handling.The triad is composed of two different membrane systems, the transverse tubule and the terminal cisternae of sarcoplasmic reticulum, in junctional association (2-4). During excitationcontraction coupling in the muscle fiber, the signal for Ca ++ release traverses this junction from t-tubule to terminal cisternae (5). As early as 1962 (6), periodic electron-dense structures were noted bridging the gap between the two types of muscle membranes. Franzini-Armstrong (7, 8) reported that these junctional "feet" (4) were arranged in repeating diamondshaped units attached to one another at the corners. The major portion of each foot seemed to be more securely attached to the terminal cisternal portion of the triad (4,7,8). A variety of interpretations have been presented that suggest roles for the intragap material in excitation-contraction coupling (9-14).In the companion paper (1), we described the isolation of purified triad structures from rabbit skeletal muscle. The present study deals with a description of the morphology of isolated triads and evaluates the susceptibility of triad structure to composition of the media, osmotic changes, and handling. MATERIALS AND METHODSOsmium tetroxide and ghitaraldehyde (vacuum distilled in glass at low temperature and the distillate treated with a special grade of high s...

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“…All the tabulated electron-probe data were obtained on unstained freeze-dried cryosections . After cryosections were obtained, the remaining portions of the muscles were processed by freeze substitution (for review, see references 10,29) for morphological studies.…”

Section: Methodsmentioning

confidence: 99%

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

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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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T‐tubule swelling in hypertonic solutions: a freeze substitution study.

Cited by 53 publications

References 35 publications

Calcium inactivation in skeletal muscle fibres of the stick insect, Carausius morosus.

Calcium inactivation in skeletal muscle fibres of the stick insect, Carausius morosus.

Morphology of isolated triads.

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

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