The concentration of free Ca2+ in the sarcoplasmic reticulum of frog cut twitch skeletal muscle fibers estimated with tetramethylmurexide

Lamboley, Cédric R.; Pape, Paul C.

doi:10.1016/j.ceca.2011.09.001

Cited by 1 publication

(12 citation statements)

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“…Four combinations of K app and [Ca 2+ ] SR,R are considered in this article, referred to as cases 1–4. For cases 1–3, the ratio [Ca 2+ ] SR / K app was 0.256, the value above obtained by Lamboley and Pape (2011). Cases 2 and 3 correspond to the lower and upper limits of [Ca 2+ ] SR,R , 0.26 and 2.35 mM, respectively, given in Section 3 of the supplemental text.…”

Section: Methodssupporting

confidence: 51%

“…7 is that the form of the [Ca 2+ ] SR (t) signal derived from a ΔA TMX signal depends on the ratio [Ca 2+ ] SR,R / K app , whereas its amplitude depends on [Ca 2+ ] SR,R . As indicated above and shown in Lamboley and Pape (2011), this ratio should be insensitive to factors affecting K app . The relatively small value for this ratio (0.256) means that the [Ca 2+ ] SR (t) signal is approximately linearly related to the ΔA TMX (t) signal.…”

Section: Methodsmentioning

confidence: 80%

“…It is evident that the forms of the binding curves for cases 1–3 are almost identical, whereas that for case 4 is quite different. (As noted above, case 4 is now ruled out by the results in Lamboley and Pape, 2011.) The reason for the difference has to do with the nonlinearity between the Δ A TMX and Δ A PR signals in Fig.…”

Section: Resultsmentioning

confidence: 96%

“…Lamboley and Pape (2011) determined the fraction of total TMX in the SR complexed with Ca (denoted as f TMX ) by permeabilizing the surface membrane of depolarized cut fibers with the detergent saponin, thereby washing out most of the TMX from the myoplasm. The average value of f TMX was 0.204 (columns 2 and 3 of Table 2 in Lamboley and Pape, 2011), which gives a value of 0.256 for the ratio [Ca 2+ ] SR / K app . As shown later, this ratio is the main determinant of the time course of [Ca 2+ ] SR ( t ) derived from the ΔA TMX signal.…”

Section: Methodsmentioning

confidence: 99%

“…The resultant information permitted estimating the full Ca-binding curve for the SR, i.e., [Ca T ] SR versus [Ca 2+ ] SR with various assumed values for resting [Ca 2+ ] SR (denoted as [Ca 2+ ] SR,R ) and the apparent dissociation constant for TMX (denoted as K app ). The first part of this article more firmly establishes the Ca-buffering properties of the SR based on the recently determined value of 0.256 for the ratio of [Ca 2+ ] SR,R / K app in Lamboley and Pape (2011), a value resulting in an approximately linear relationship between the absorbance signal from TMX and [Ca 2+ ] SR (t). Nonlinearity between [Ca T ] SR and [Ca 2+ ] SR , more firmly established here, indicates a significant degree of cooperativity likely arising mainly from calsequestrin, a high capacity Ca-binding protein in the SR discovered by MacLennan and Wong (1971).…”

Section: Introductionmentioning

confidence: 96%

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Calcium buffering properties of sarcoplasmic reticulum and calcium-induced Ca2+ release during the quasi-steady level of release in twitch fibers from frog skeletal muscle

Fénelon

Lamboley

Carrier

et al. 2012

Journal of General Physiology

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Experiments were performed to characterize the properties of the intrinsic Ca2+ buffers in the sarcoplasmic reticulum (SR) of cut fibers from frog twitch muscle. The concentrations of total and free calcium ions within the SR ([CaT]SR and [Ca2+]SR) were measured, respectively, with the EGTA/phenol red method and tetramethylmurexide (a low affinity Ca2+ indicator). Results indicate SR Ca2+ buffering was consistent with a single cooperative-binding component or a combination of a cooperative-binding component and a linear binding component accounting for 20% or less of the bound Ca2+. Under the assumption of a single cooperative-binding component, the most likely resting values of [Ca2+]SR and [CaT]SR are 0.67 and 17.1 mM, respectively, and the dissociation constant, Hill coefficient, and concentration of the Ca-binding sites are 0.78 mM, 3.0, and 44 mM, respectively. This information can be used to calculate a variable proportional to the Ca2+ permeability of the SR, namely d[CaT]SR/dt ÷ [Ca2+]SR (denoted release permeability), in experiments in which only [CaT]SR or [Ca2+]SR is measured. In response to a voltage-clamp step to −20 mV at 15°C, the release permeability reaches an early peak followed by a rapid decline to a quasi-steady level that lasts ∼50 ms, followed by a slower decline during which the release permeability decreases by at least threefold. During the quasi-steady level of release, the release amplitude is 3.3-fold greater than expected from voltage activation alone, a result consistent with the recruitment by Ca-induced Ca2+ release of 2.3 SR Ca2+ release channels neighboring each channel activated by its associated voltage sensor. Release permeability at −60 mV increases as [CaT]SR decreases from its resting physiological level to ∼0.1 of this level. This result argues against a release termination mechanism proposed in mammalian muscle fibers in which a luminal sensor of [Ca2+]SR inhibits release when [CaT]SR declines to a low level.

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Section: Methodssupporting

confidence: 51%

Section: Methodsmentioning

confidence: 80%

Section: Resultsmentioning

confidence: 96%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

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