scholarly journals 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

2012 ◽  
Vol 140 (4) ◽  
pp. 403-419 ◽  
Author(s):  
Karine Fénelon ◽  
Cédric R.H. Lamboley ◽  
Nicole Carrier ◽  
Paul C. Pape
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Hill Coefficient ◽  
Free Calcium ◽  
Rapid Decline ◽  
Cooperative Binding ◽  
Phenol Red ◽  
Physiological Level ◽  
Steady Level ◽  
Early Peak ◽  
Binding Component

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.

scholarly journals Perturbation of sarcoplasmic reticulum calcium release and phenol red absorbance transients by large concentrations of fura-2 injected into frog skeletal muscle fibers.

1990 ◽  
Vol 96 (3) ◽  
pp. 493-516 ◽  
Author(s):  
P C Pape ◽  
M Konishi ◽  
S Hollingworth ◽  
S M Baylor
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Action Potential ◽  
Time Course ◽  
Calcium Release ◽  
Free Calcium ◽  
Phenol Red ◽  
Charge Balance ◽  
Ph Change ◽  
Single Action ◽  
Fura 2

Intact single twitch fibers from frog muscle were studied on an optical bench apparatus after micro-injection with two indicator dyes: phenol red, to monitor a previously described signal (denoted delta pHapp; Hollingworth and Baylor. 1990. J. Gen. Physiol. 96:473-491) possibly reflective of a myoplasmic pH change following action potential stimulation; and fura-2, to monitor the associated change in the myoplasmic free calcium concentration (delta[Ca2+]). Additionally, it was expected that large myoplasmic concentrations of fura-2 (0.5-1.5 mM) might alter delta pHapp, since it was previously found (Baylor and Hollingworth. 1988. J. Physiol. 403:151-192) that the Ca2(+)-buffering effects of large fura-2 concentrations: (a) increase the estimated total concentration of Ca2+ (denoted by delta[CaT]) released from the sarcoplasmic reticulum (SR), but (b) reduce and abbreviate delta[Ca2+]. The experiments show that delta pHapp was increased at the larger fura-2 concentrations; moreover, the increase in delta pHapp was approximately in proportion to the increase in delta[CaT]. At all fura-2 concentrations, the time course of delta pHapp, through time to peak, was closely similar to, although probably slightly slower than, that of delta[CaT]. These properties of delta pHapp are consistent with an hypothesis proposed by Meissner and Young (1980. J. Biol. Chem. 255:6814-6819) and Somlyo et al. (1981. J. Cell Biol. 90:577-594) that a proton flux from the myoplasm into the SR supplies a portion of the electrical charge balance required as Ca2+ is released from the SR into the myoplasm. A comparison of the amplitude of delta pHapp with that of delta[CaT] indicates that, in response to a single action potential, 10-15% of the charge balance required for Ca2+ release may be carried by protons.

Alteration of Acylphosphate Formation of Cardiac Sarcoplasmic Reticulum ATPase by Calmodulin-Dependent Phosphorylation

1984 ◽  
Vol 39 (3-4) ◽  
pp. 289-292 ◽  
Author(s):  
Christian Pifl ◽  
Brigitte Plank ◽  
Gertrude Hellmann ◽  
Wolfgang Wyskovsky ◽  
Josef Suko
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Transport ◽  
State Level ◽  
Hill Coefficient ◽  
Free Calcium ◽  
Sr Protein ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Transport Atpase ◽  
Calcium Dependent ◽  
Calcium Calmodulin Dependent

The calcium-dependent acylphosphate formed by the calcium transport ATPase of cardiac sarcoplasmic reticulum and the calcium-, calm odulin-dependent phosphoester(s) of sarcoplasmic reticulum fractions formed by a calcium-, calmodulin-dependent membrane-bound protein kinase can be distinguished by removal of calcium and/or magnesium by EDTA or hydroxylamine treatment of the acid denaturated membranes. Both procedures decompose the acylphosphate with little effect on the phosphoester(s). Calmodulin-dependent phosphorylation (2.44 nmol/mg SR protein) reduces the apparent K(Ca) of the acylphosphate steady state level of the calcium transport ATPase from 0.56 to 0.34 μM free calcium, without affecting the maximum phosphoenzyme level (0.93 versus 0.89 nmol/mg protein), and has little, if any, effect on the Hill-coefficient (1.32 versus 1.54)

scholarly journals Feeding wet distillers grains plus solubles contributes to sarcoplasmic reticulum membrane instability

2018 ◽  
Vol 58 (12) ◽  
pp. 2215 ◽  
Author(s):  
M. D. Chao ◽  
K. I. Domenech-Perez ◽  
L. S. Senaratne-Lenagala ◽  
C. R. Calkins
Keyword(s):  
Fatty Acid ◽  
Sarcoplasmic Reticulum ◽  
Lipid Oxidation ◽  
Neutral Lipid ◽  
Sarcomere Length ◽  
Membrane Integrity ◽  
Distillers Grains ◽  
Free Calcium ◽  
Post Mortem ◽  
Wet Distillers Grains

Feeding wet distillers grains plus solubles (WDGS) increases polyunsaturated fatty acid (PUFA) levels in beef. It was hypothesised that WDGS in feedlot diets increases PUFA concentration in the sarcoplasmic reticulum (SR) membrane, thereby altering membrane integrity, resulting in more rapid intracellular calcium leakage and improved tenderness. The objective of this study was to evaluate this hypothesis. Ninety-six crossbred steers were fed either a corn-based diet with 0% WDGS or 50% WDGS. Fifteen strip loins per treatment were collected, fabricated into steaks, aged and placed under retail display conditions. Steaks were used to measure tenderness, proteolysis, free calcium concentrations, lipid oxidation, sarcomere length and SR membrane fatty acid, phospholipid lipid, neutral lipid and total lipid profiles. Compared with steaks from steers fed 0% WDGS, steaks from steers fed 50% WDGS were more tender (P < 0.05) and had greater (P < 0.05) free calcium concentrations early post-mortem. Feeding 50% WDGS also tended to increase (P < 0.10) total PUFA concentrations, decrease (P < 0.10) total phospholipid concentration and increase (P < 0.10) total neutral lipid concentration for SR membrane. Steaks from steers fed 0% WDGS had greater (P < 0.05) lipid oxidation (TBARS values) than steaks from steers fed 50% WDGS after extended aging. Although differences in tenderness between the two treatments were detected, there were no corresponding differences (P > 0.10) in sarcomere length or proteolysis. This study showed that feeding WDGS may increase tenderness, possibly by increasing free calcium in muscle early post-mortem. However, the true mechanism that contributes to these differences is still unclear.

Effects of ischemia on sarcoplasmic reticulum and contractile myofilament activity in human myocardium

1993 ◽  
Vol 265 (4) ◽  
pp. H1334-H1341 ◽  
Author(s):  
G. B. Luciani ◽  
A. D'Agnolo ◽  
A. Mazzucco ◽  
V. Gallucci ◽  
G. Salviati
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Heart Surgery ◽  
Open Heart Surgery ◽  
Isometric Tension ◽  
Hill Coefficient ◽  
Calmodulin Antagonist ◽  
Contractile System ◽  
Cardiac Fiber ◽  
And Control

The effects of global ischemia on the contractile system and on sarcoplasmic reticulum (SR) function were studied by measuring the isometric tension and the SR Ca2+ release activity of chemically skinned cardiac fiber preparations from seven patients undergoing open-heart surgery. Ten minutes of ischemia caused 1) a decrease in the myofilament sensitivity to Ca2+ (expected Ca2+ concentration giving half-maximal tension; from 0.69 +/- 0.04 to 1.38 +/- 0.06 microM, n = 7) and in the cooperativity index (Hill coefficient; from 2.61 +/- 0.45 to 0.92 +/- 0.15, n = 7), 2) a decrease in myosin light chain phosphorylation, and 3) a 300% increase in the threshold caffeine concentration for SR Ca2+ efflux channel activation, with a 30% reduction in the rate of Ca2+ release by caffeine at threshold concentrations and a 23% reduction in the rate of release by 20 mM caffeine. After preincubation with 5 microM trifluoperazine, a calmodulin antagonist, the caffeine threshold of ischemic and control cardiac muscle became comparable. Most changes were reversed by reperfusion, while the caffeine threshold was still two times greater than control. These results indicate that ischemia caused alterations of the cardiac muscle contractile apparatus and the SR that were reversed only after reperfusion.

The Effect of Calcium and Phosphate on the Biphasic Calcium Uptake by the Sarcoplasmic Reticulum

1975 ◽  
Vol 30 (11-12) ◽  
pp. 777-780 ◽  
Author(s):  
Pierre Ermier ◽  
Wilhelm Hasselbach
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Inorganic Phosphate ◽  
Calcium Uptake ◽  
Initial Rate ◽  
Maximum Amplitude ◽  
Phosphate Concentration ◽  
Free Calcium ◽  
Physiological Range ◽  
External Calcium

Abstract The amplitude of the fast uptake and the initial rate of the slow uptake increase with in­ creasing free calcium concentrations, up to 30 μᴍ. In that range, both processes are correlated to each other. At higher concentrations, the slow uptake is more inhibited than the fast uptake. The fast uptake shows a maximum amplitude which remains unchanged in the presence of phosphate. The slow uptake leads to a nearly complete depletion of the external calcium, and its rate is proportional to the phosphate concentration, even at physiological range. The sarcoplasmic ATPase liberates inorganic phosphate and the slow uptake

Mechanism of ischemic contracture in ferret hearts: relative roles of [Ca2+]i elevation and ATP depletion

1990 ◽  
Vol 258 (1) ◽  
pp. H9-H16 ◽  
Author(s):  
Y. Koretsune ◽  
E. Marban
Keyword(s):  
Atp Depletion ◽  
Free Calcium ◽  
Coronary Perfusion ◽  
Ischemic Contracture ◽  
Steady Level ◽  
Intracellular Free Calcium Concentration ◽  
Free Calcium Concentration ◽  
Cross Bridges ◽  
Time Required ◽  
Mean Time

When coronary perfusion is interrupted, the diastolic force generated by the myocardium first falls but eventually increases. The delayed rise in force, ischemic contracture, has been attributed either to ATP depletion or to elevation of the intracellular free calcium concentration ([Ca2+]i). To distinguish between these possibilities, we measured [Ca2+]i and ATP concentration [( ATP]) in ferret hearts using nuclear magnetic resonance (NMR) spectroscopy. Mean time-average [Ca2+]i and [ATP] equaled 0.25 microM and 2.7 mumol/g wet wt, respectively, under control perfusion conditions. [Ca2+]i increased and [ATP] fell during total global ischemia. Although [Ca2+]i exceeded the usual systolic levels of 1.7 microM within 20-25 min of ischemia and reached a steady level between 2 and 3 microM by 30-35 min, force only began to rise after 40 min. In contrast, the time required for [ATP] to fall to less than 10% of control levels coincided closely with the onset of contracture. Ischemia in the presence of iodoacetate, an inhibitor of glycolysis, led to a precipitous fall in [ATP] and a concomitant rise in force, both of which preceded any elevation of [Ca2+]i. Thus changes in [Ca2+]i are neither sufficient nor necessary for the initiation of ischemic contracture. We conclude that ATP depletion is primary and that the rise in resting force reflects the formation of rigor cross bridges.

Calcium-dependent halothane activation of sarcoplasmic reticulum calcium channels from frog skeletal muscle

1994 ◽  
Vol 266 (2) ◽  
pp. C391-C396 ◽  
Author(s):  
R. Bull ◽  
J. J. Marengo
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Calcium Channels ◽  
Lipid Bilayers ◽  
Single Channel ◽  
Free Calcium ◽  
Frog Skeletal Muscle ◽  
Time Constants ◽  
Calcium Dependent ◽  
Open Time

The effect of halothane on calcium channels present in sarcoplasmic reticulum membranes isolated from frog skeletal muscle was studied at the single channel level after fusing the isolated vesicles into planar lipid bilayers. Addition of 91 microM halothane to the cytosolic compartment containing 1 microM free calcium activated the channel by increasing fractional open time from 0.11 to 0.59, without changing the channel conductance. The activation of the channels by halothane was calcium dependent. At resting calcium concentrations in the cytosolic compartment, halothane failed to activate the channel, whereas maximal activation was found at 10 microM calcium. The free energy of halothane binding to the channel decreased from -5.8 kcal/mol at 1 microM calcium to -6.6 kcal/mol at 10 microM calcium. Halothane increased the open time constants and decreased the closed time constants, indicating that it binds to both the open and the closed configurations of the channel.

Contraction and intracellular Ca2+, Na+, and H+ during acidosis in rat ventricular myocytes

1992 ◽  
Vol 262 (2) ◽  
pp. C348-C357 ◽  
Author(s):  
S. M. Harrison ◽  
J. E. Frampton ◽  
E. McCall ◽  
M. R. Boyett ◽  
C. H. Orchard
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Intracellular Ph ◽  
Fluorescent Dyes ◽  
Ventricular Myocytes ◽  
Respiratory Acidosis ◽  
Exchange Mechanism ◽  
Rapid Decline ◽  
Partial Recovery ◽  
Slow Recovery ◽  
Initial Exposure

We have investigated the effect of a CO2-induced (respiratory) acidosis on contraction and on intracellular Ca2+, Na+, and pH (measured using the fluorescent dyes fura-2, sodium-binding benzofuran isophthalate, and 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein, respectively) in ventricular myocytes isolated from rat hearts. Initial exposure to acidosis led to a rapid decrease in intracellular pH that was accompanied by an abrupt decline in contractility. There were no consistent changes of intracellular Na+ or Ca2+ during this period. The rapid decline of contractility was followed by a slower partial recovery, which was accompanied by increases in intracellular Na+, systolic and diastolic Ca2+, and an increase in the Ca2+ content of the sarcoplasmic reticulum (estimated using caffeine). Intracellular pH did not change during this slow recovery. The slow rise of intracellular Na+ and the recovery of the twitch were blocked by the Na(+)-H+ exchange inhibitor amiloride. The sarcoplasmic reticulum inhibitor ryanodine blocked the recovery of the twitch but had no effect on the rise of intracellular Na+ induced during acidosis. It is concluded that a major cause of the initial decline of the twitch during acidosis is a decrease in the response of the contractile proteins to Ca2+ due to the decrease of intracellular pH. The subsequent slow recovery of the twitch is due to the decrease of intracellular pH activating the Na(+)-H+ exchange mechanism. This elevates intracellular Na+ and presumably, via the Na(+)-Ca2+ exchange mechanism, intracellular Ca2+. This in turn may lead to increased Ca2+ loading of, and hence release from, the sarcoplasmic reticulum, and it is this that underlies the partial recovery of contraction during acidosis in this preparation.

scholarly journals Adaptations in human muscle sarcoplasmic reticulum to prolonged submaximal training

2003 ◽  
Vol 94 (5) ◽  
pp. 2034-2042 ◽  
Author(s):  
H. J. Green ◽  
C. S. Ballantyne ◽  
J. D. MacDougall ◽  
M. A. Tarnopolsky ◽  
J. D. Schertzer
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Atpase Activity ◽  
Vastus Lateralis ◽  
Training Session ◽  
Maximal Activity ◽  
Hill Coefficient ◽  
Protein Levels ◽  
Plasmic Reticulum ◽  
Cycle Training ◽  
The Hill

In this study, we employed single-leg submaximal cycle training, conducted over a 10-wk period, to investigate adaptations in sarcoplasmic reticulum (SR) Ca2+-regulatory proteins and processes of the vastus lateralis. During the final weeks, the untrained volunteers (age 21.4 ± 0.3 yr; means ± SE, n = 10) were exercising 5 times/wk and for 60 min/session. Analyses were performed on tissue extracted by needle biopsy ∼4 days after the last training session. Compared with the control leg, the trained leg displayed a 19% reduction ( P < 0.05) in homogenate maximal Ca2+-ATPase activity (192 ± 11 vs. 156 ± 18 μmol · g protein−1 · min−1), a 4.3% increase ( P < 0.05) in pCa50, defined as the Ca2+ concentration at half-maximal activity (6.01 ± 0.05 vs. 6.26 ± 0.07), and no change in the Hill coefficient (1.75 ± 0.15 vs. 1.76 ± 0.21). Western blot analysis using monoclonal antibodies (7E6 and A52) revealed a 13% lower ( P < 0.05) sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) 1 in trained vs. control in the absence of differences in SERCA2a. Training also resulted in an 18% lower ( P < 0.05) SR Ca2+ uptake and a 26% lower ( P < 0.05) Ca2+ release. It is concluded that a downregulation in SR Ca2+ cycling in vastus lateralis occurs with aerobic-based training, which at least in the case of Ca2+ uptake can be explained by reduction in Ca2+-ATPase activity and SERCA1 protein levels.

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