Questions about adaptation in ryanodine receptors.
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Action Potentials↗
Biomedical subjects
D G Stephenson
Publications and source records attributed to D G Stephenson.
Effects of dihydropyridine receptor II-III loop peptides on Ca(2+) release in skinned skeletal muscle fibers.
In skeletal muscle fibers, the intracellular loop between domains II and III of the alpha(1)-subunit of the dihydropyridine receptor (DHPR) may directly activate the adjacent Ca(2+) release channel in the sarcoplasmic reticulum. We examined the effects of synthetic peptide segments of this loop on Ca(2+) release in mechanically skinned skeletal muscle fibers with functional excitation-contraction coupling. In rat fibers at physiological Mg(2+) concentration ([Mg(2+)]; 1 mM), a 20-residue skeletal muscle DHPR peptide [A(S(20)); Thr(671)-Leu(690); 30 microM], shown previously to induce Ca(2+) release in a triad preparation, caused only small spontaneous force responses in approximately 40% of fibers, although it potentiated responses to depolarization and caffeine in all fibers. The COOH-terminal half of A(S(20)) [A(S(10))] induced much larger spontaneous responses but also caused substantial inhibition of Ca(2+) release to both depolarization and caffeine. Both peptides induced or potentiated Ca(2+) release even when the voltage sensors were inactivated, indicating direct action on the Ca(2+) release channels. The corresponding 20-residue cardiac DHPR peptide [A(C(20)); Thr(793)-Ala(812)] was ineffective, but its COOH-terminal half [A(C(10))] had effects similar to A(S(20)). In the presence of lower [Mg(2+)] (0.2 mM), exposure to either A(S(20)) or A(C(10)) (30 microM) induced substantial Ca(2+) release. Peptide C(S) (100 microM), a loop segment reported to inhibit Ca(2+) release in triads, caused partial inhibition of depolarization-induced Ca(2+) release. In toad fibers, each of the A peptides had effects similar to or greater than those in rat fibers. These findings suggest that the A and C regions of the skeletal DHPR II-III loop may have important roles in vivo.
Amino Acid Sequence↗
MHC isoform composition and Ca(2+)- or Sr(2+)-activation properties of rat skeletal muscle fibers.
Chemically skinned single fibers from adult rat skeletal muscles were used to test the hypothesis that, in mammalian muscle fibers, myosin heavy chain (MHC) isoform expression and Ca(2+)- or Sr(2+)-activation characteristics are only partly correlated. The fibers were first activated in Ca(2+)- or Sr(2+)-buffered solutions under near-physiological conditions, and then their MHC isoform composition was determined electrophoretically. Fibers expressing only the MHC I isoform could be appropriately identified on the basis of either the Ca(2+)- or Sr(2+)-activation characteristics or the MHC isoform composition. Fibers expressing one or a combination of fast MHC isoforms displayed no significant differences in their Ca(2+)- or Sr(2+)-activation properties; therefore, their MHC isoform composition could not be predicted from their Ca(2+)- or Sr(2+)-activation characteristics. A large proportion of fibers expressing both fast- and slow-twitch MHC isoforms displayed Ca(2+)- or Sr(2+)-activation properties that were not consistent with their MHC isoform composition; thus both fiber-typing methods were needed to fully characterize such fibers. These data show that, in rat skeletal muscles, the extent of correlation between MHC isoform expression and Ca(2+)- or Sr(2+)-activation characteristics is fiber-type dependent.
Animals↗
Glycogen content and excitation-contraction coupling in mechanically skinned muscle fibres of the cane toad.
1. Mechanically skinned skeletal muscle fibres from the twitch region of the iliofibularis muscle of cane toads were used to investigate the relationship between fibre glycogen content and fibre capacity to respond to transverse tubular (T-) system depolarization. 2. A large proportion of total fibre glycogen remained in mechanically skinned muscle fibres exposed to aqueous solutions. This glycogen pool (about 80% of total fibre glycogen) was very stable when the preparation was incubated in a rigor solution (pH 7.0) but decreased gradually at a rate of 0.59+/-0.20% min-1 in a relaxing solution (200 nM [Ca2+]). The rate was considerably higher (2.66+/-0.38% min(-1)) when the preparations were exposed to 30 microM [Ca2+]. An even greater rate of glycogen loss was found after T-system depolarization-induced contractions. The Ca2+-dependent loss of fibre glycogen was caused by endogenous glycogenolytic processes. 3. Silver stained SDS gels of components eluted into relaxing solution from single skinned fibres revealed a rapid (2 min) loss of parvalbumin and at least 10 other proteins varying in molecular mass between 10 and 80 kDa but there was essentially no loss of myosin heavy and light chains and actin. Subsequent elution for a further 30 min in either relaxing or maximally Ca2+-activating solution did not result in additional, appreciable detectable loss of fibre protein. 4. Depletion of fibre glycogen was associated with loss of fibre ability to respond to T-system depolarization even though the bathing solutions contained high levels of ATP (8 mM) and creatine phosphate (10 mM). 5. The capacity of mechanically skinned fibres to respond to T-system depolarization was highly positively correlated (P<0.0001) with initial fibre glycogen concentration. 6. In conclusion, the results show that (i) the capacity of skeletal muscle to respond to T-system depolarization is related directly or indirectly to the non-washable glycogen pool in fibres, (ii) this relationship holds for conditions where glycogen is not required as a source of energy and (iii) the mechanically skinned fibre preparation is well suited to study the regulation of endogenous glycogenolytic enzymes.
Adenosine Triphosphate↗
Effects of beta-escin and saponin on the transverse-tubular system and sarcoplasmic reticulum membranes of rat and toad skeletal muscle.
Mechanically skinned skeletal muscle fibres from rat and toad were exposed to the permeabilizing agents beta-escin and saponin. The effects of these agents on the sealed transverse tubular system (t-system) and sarcoplasmic reticulum (SR) were examined by looking at changes in the magnitude of the force responses to t-system depolarization, the time course of the fluorescence of fura-2 trapped in the sealed t-system, and changes in the magnitude of caffeine-induced contractures following SR loading with Ca2+ under defined conditions. In the presence of 2 microg ml-1 beta-escin and saponin, the response to t-system depolarization was not completely abolished, decreasing to a plateau, and a large proportion of fura-2 remained in the sealed t-system. At 10 microg ml-1, both agents abolished the ability of both rat and toad preparations to respond to t-system depolarization after 3 min of exposure, but a significant amount of fura-2 remained in sealed t-tubules even after exposure to 100 microg ml-1 beta-escin and saponin for 10 min. beta-Escin took longer than saponin to reduce the t-system depolarizations and fura-2 content of the sealed t-system to a similar level. The ability of the SR to load Ca2+ was reduced to a lower level after treatment with beta-escin than saponin. This direct effect on the SR occurred at much lower concentrations for rat (2 microg ml-1 beta-escin and 10 microg ml-1 saponin) than toad (10 microg ml-1 beta-escin and 150 microg ml-1 saponin). The reverse order in sensitivities to beta-escin and saponin of t-system and SR membranes indicates that the mechanisms of action of beta-escin and saponin are different in the two types of membrane. In conclusion, this study shows that: (1) beta-escin has a milder action on the surface membrane than saponin; (2) beta-escin is a more potent modifier of SR function; (3) simple permeabilization of membranes is not sufficient to explain the effects of beta-escin and saponin on muscle membranes; and (4) the t-system network within muscle fibres is not a homogeneous compartment.
Animals↗
Caffeine and excitation-contraction coupling in skeletal muscle: a stimulating story.
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Animals↗
Fiber type populations and Ca2+-activation properties of single fibers in soleus muscles from SHR and WKY rats.
Electrophoretic analyses of muscle proteins in whole muscle homogenates and single muscle fiber segments were used to examine myosin heavy chain (MHC) and myosin light chain 2 (MLC2) isoform composition and fiber type populations in soleus muscles from spontaneously hypertensive rats (SHRs) and their age-matched normotensive controls [Wistar-Kyoto (WKY) rats], at three stages in the development of high blood pressure (4 wk, 16 wk, and 24 wk of age). Demembranated (chemically skinned with 2% Triton X-100), single fiber preparations were used to determine the maximum Ca2+-activated force per cross-sectional area, calcium sensitivity, and degree of cooperativity of the contractile apparatus and Ca2+-regulatory system with respect to Ca2+. The results show that, at all ages examined, 1) SHR soleus contained a lower proportion of MHCI and MLC2 slow (MLC2s) and a higher proportion of MHCIIa, MHCIId/x, and MLC2 fast (MLC2f ) isoforms than the age-matched controls; 2) random dissection of single fibers from SHR and WKY soleus produced four populations of fibers: type I (expressing MHCI), type IIA (expressing MHCIIa), hybrid type I+IIA (coexpressing MHCI and MHCIIa), and hybrid type IIA+IID (coexpressing MHCIIa and MHCIId/x); and 3) single fiber dissection from SHR soleus yielded a lower proportion of type I fibers, a higher proportion of fast-twitch fibers (types IIA and IIA+IID), and a higher proportion of hybrid fibers (types I+IIA and IIA+IID) than the homologous muscles from the age-matched WKY rats. Because the presence of hybrid fibers is viewed as a marker of muscle transformation, these data suggest that SHR soleus undergoes transformation well into adulthood. Our data show also that, for a given fiber type, there are no significant differences between SHR and WKY soleus muscles with respect to any of the Ca2+-activation properties examined. This finding indicates that the lower specific tensions reported in the literature for SHR soleus muscles are not due to strain- or hypertension-related differences in the function of the contractile apparatus or regulatory system.
Animals↗
A direct microfluorometric method for measuring subpicomole amounts of nicotinamide adenine dinucleotide phosphate, glucose, and glycogen.
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Animals↗
Microfluorometric analyses of glycogen in freshly dissected, single skeletal muscle fibres of the cane toad using a mechanically skinned fibre preparation.
The main objective of this study was to analyse glycogen in single muscle fibres, using a recently developed microfluorometric method which detects subpicomol amounts of NADPH, glucose and glycogen (as glucosyl units) (detection limit 0.16-0.17 pmol in a 25 nl sample) without fluorochrome amplification. The fibres were freshly dissected from the twitch region of the iliofibularis muscle of the cane toad (Bufo marinus), and were mechanically skinned under paraffin oil to gain access to the intracellular compartments. The results show that (1) glycogen concentrations in toad skeletal muscle fibres range between 25.8 and 369 mmol glucosyl units/litre fibre volume; (2) there is a large variation in glycogen content between individual fibres from the iliofibularis muscle of one animal; (3) there are seasonal differences in the glycogen content of toad single muscle fibres; (4) the total amount of glycogen in single muscle fibres of the toad does not decrease significantly when storing the tissue, under paraffin oil, at 20-25 degree C for up to 6 h or at 4 degree C for up to 24 h; and (5) 15-26% of fibre glycogen can be washed in an aqueous solution at pH 5-7, within 5 min, while 74-85% of fibre glycogen remains associated with the washed skinned fibre, even after 40 min exposure of the skinned fibre preparation to the aqueous environment. The retention of most glycogen in the fibre preparation after mechanical removal of the plasma membrane and extensive washing indicates that in toad skeletal muscle fibres the largest proportion of glycogen is tightly bound to intracellular structures. The results also show that the skinned muscle fibre preparation is well suited for microfluorometric glycogen determination, since low molecular weight non-glycogen contributors to the fluorescence signal can be removed from the myoplasmic space prior to the glycogen hydrolysis step.
Animals↗
Events of the excitation-contraction-relaxation (E-C-R) cycle in fast- and slow-twitch mammalian muscle fibres relevant to muscle fatigue.
The excitation-contraction-relaxation cycle (E-C-R) in the mammalian twitch muscle comprises the following major events: (1) initiation and propagation of an action potential along the sarcolemma and transverse (T)-tubular system; (2) detection of the T-system depolarization signal and signal transmission from the T-tubule to the sarcoplasmic reticulum (SR) membrane; (3) Ca2+ release from the SR; (4) transient rise of myoplasmic [Ca2+]; (5) transient activation of the Ca2+-regulatory system and of the contractile apparatus; (6) Ca2+ reuptake by the SR Ca2+ pump and Ca2+ binding to myoplasmic sites. There are many steps in the E-C-R cycle which can be seen as potential sites for muscle fatigue and this review explores how structural and functional differences between the fast- and slow-twitch fibres with respect to the E-C-R cycle events can explain to a great extent differences in their fatiguability profiles.
Animals↗
Effect of clenbuterol on sarcoplasmic reticulum function in single skinned mammalian skeletal muscle fibers.
We examined the effect of the beta2-agonist clenbuterol (50 microM) on depolarization-induced force responses and sarcoplasmic reticulum (SR) function in muscle fibers of the rat (Rattus norvegicus; killed by halothane overdose) that had been mechanically skinned, rendering the beta2-agonist pathway inoperable. Clenbuterol decreased the peak of depolarization-induced force responses in the extensor digitorum longus (EDL) and soleus fibers to 77.2 +/- 9.0 and 55.6 +/- 5.4%, respectively, of controls. The soleus fibers did not recover. Clenbuterol significantly and reversibly reduced SR Ca2+ loading in EDL and soleus fibers to 81.5 +/- 2.8 and 78.7 +/- 4.0%, respectively, of controls. Clenbuterol also produced an approximately 25% increase in passive leak of Ca2+ from the SR of the EDL and soleus fibers. These results indicate that clenbuterol has direct effects on fast- and slow-twitch skeletal muscle, in the absence of the beta2-agonist pathway. The increased Ca2+ leak in the triad region may lead to excitation-contraction coupling damage in the soleus fibers and could also contribute to the anabolic effect of clenbuterol in vivo.
Adrenergic beta-Agonists↗
Effect of saponin treatment on the sarcoplasmic reticulum of rat, cane toad and crustacean (yabby) skeletal muscle.
1. Mechanically skinned fibres from skeletal muscles of the rat, toad and yabby were used to investigate the effect of saponin treatment on sarcoplasmic reticulum (SR) Ca2+ loading properties. The SR was loaded submaximally under control conditions before and after treatment with saponin and SR Ca2+ was released with caffeine. 2. Treatment with 10 micrograms ml-1 saponin greatly reduced the SR Ca2+ loading ability of skinned fibres from the extensor digitorum longus muscle of the rat with a rate constant of 0.24 min-1. Saponin concentrations up to 150 micrograms ml-1 and increased exposure time up to 30 min did not further reduce the SR Ca2+ loading ability of the SR, which indicates that the inhibitory action of 10-150 micrograms ml-1 saponin is not dose dependent. The effect of saponin was also not dependent on the state of polarization of the transverse-tubular system. 3. Treatment with saponin at concentrations up to 100 micrograms ml-1 for 30 min did not affect the Ca2+ loading ability of SR in skinned skeletal muscle fibres from the twitch portion of the toad iliofibularis muscle but SR Ca2+ loading ability decreased markedly with a time constant of 0.22 min-1 in the presence of 150 micrograms ml-1 saponin. 4. The saponin dependent increase in permeability could be reversed in both rat and toad fibres by short treatment with 6 microM Ruthenium Red, a potent SR Ca2+ channel blocker, suggesting that saponin does affect the SR Ca2+ channel properties in mammalian and anuran skeletal muscle. 5. Treatment of skinned fibres of long sarcomere length (> 6 microns) from the claw muscle of the yabby (a freshwater decapod crustacean) with 10 micrograms ml-1 saponin for 30 min abolished the ability of the SR to load Ca2+, indicating that saponin affects differently the SR from skeletal muscles of mammals, anurans and crustaceans. 6. It is concluded that at relatively low concentrations, saponin causes inhibition of the skeletal SR Ca2+ loading ability in a species dependent manner, probably by increasing the Ca2+ loss through SR Ca2+ release channels.
Animals↗
Relationship between depolarization-induced force responses and Ca2+ content in skeletal muscle fibres of rat and toad.
1. The relationship between the total Ca2+ content of a muscle fibre and the magnitude of the force response to depolarization was examined in mechanically skinned fibres from the iliofibularis muscle of the toad and the extensor digitorum longus muscle of the rat. The response to depolarization in each skinned fibre was assessed either at the endogenous level of Ca2+ content or after depleting the fibre of Ca2+ to some degree. Ca2+ content was determined by a fibre lysing technique. 2. In both muscle types, the total Ca2+ content could be reduced from the endogenous level of approximately 1.3 mmol l-1 (expressed relative to intact fibre volume) to approximately 0.25 mmol l-1 by either depolarization or caffeine application in the presence of Ca2+ chelators, showing that the great majority of the Ca2+ was stored in the sarcoplasmic reticulum (SR). Chelation of Ca2+ in the transverse tubular (T-) system, either by exposure of fibres to EGTA before skinning or by permeabilizing the T-system with saponin after skinning, reduced the lower limit of Ca2+ content to < or = 0.12 mmol l-1, indicating that 10-20% of the total fibre Ca2+ resided in the T-system. 3. In toad fibres, both the peak and the area (i.e. time integral) of the force response to depolarization were reduced by any reduction in SR Ca2+ content, with both decreasing to zero in an approximately linear manner as the SR Ca2+ content was reduced to < 15% of the endogenous level. In rat fibres, the peak size of the force response was less affected by small decreases in SR content, but both the peak and area of the response decreased to zero with greater depletion. In partially depleted toad fibres, inhibition of SR Ca2+ uptake potentiated the force response to depolarization almost 2-fold. 4. The results show that in this skinned fibre preparation: (a) T-system depolarization and caffeine application can each virtually fully deplete the SR of Ca2+, irrespective of any putative inhibitory effect of SR depletion on channel activation; (b) all of the endogenous level of SR Ca2+ must be released in order to produce a maximal response to depolarization; and (c) a substantial part (approximately 40%) of the Ca2+ released by a depolarization is normally taken back into the SR before it can contribute to force production.
Animals↗
Time course of calcium transients derived from Fura-2 fluorescence measurements in single fast twitch fibres of adult mice and rat myotubes developing in primary culture.
In this study, we applied a method to correct for the altered binding kinetics of Fura-2 for Ca2+ in vivo, on Ca2+ fluorescence transients (Ca2+F) measured using Fura-2 in single adult fast twitch skeletal muscle fibres of the mouse, which exhibit very fast [Ca2+] responses, and rat myotubes developing in culture which exhibit slower [Ca2+] responses (rise time [20-80% of peak] of Ca2+F transients: 1.81 +/- 0.17 ms and 16.14 +/- 2.60 ms, respectively). After correction, the [Ca2+] transients (Ca2+C) measured in both the adult mouse fibres and the myotubes rose more rapidly (mean rise time of Ca2+C transients: adult mouse fibres, 0.76 +/- 0.12 ms; rat myotubes, 8.25 +/- 2.83 ms) and often exhibited a Ca2+ spike which exceeded the peak of the Ca2+F transient. In the adult mouse fibres, correction increased the mean peak [Ca2+] of the Ca2+F transients by a factor of 7 from 0.53 +/- 0.08 microM to 3.76 +/- 0.71 microM. The accuracy of the time course of the corrected Ca2+ transients was confirmed by comparison to the time course of Ca2+ transients measured with Mag-Fura-5, which had a similar mean rise time (0.94 +/- 0.10 ms, t-test, P = 0.80). The more slowly rising Ca2+ transients measured in the rat myotubes were less affected by the correction process, increasing in mean peak [Ca2+] by a factor of only 1.2 from 0.82 +/- 0.17 microM to 0.97 +/- 0.15 microM. During the decay phase of the Ca2+ transients elicited in the adult mouse fibres and the myotubes, the corrected Ca2+C signal largely followed the unmodified Ca2+F transient. The correction process was found to have little effect on Ca2+ transients with rise time values greater than 10 ms, which included most of the Ca2+ transients measured in the myotubes.
Animals↗
Phosphate transport into the sarcoplasmic reticulum of skinned fibres from rat skeletal muscle.
The rate, magnitude and pharmacology of inorganic phosphate (Pi) transport into the sarcoplasmic reticulum were estimated in single, mechanically skinned skeletal muscle fibres of the rat. This was done, indirectly, by using a technique that measured the total Ca2+ content of the sarcoplasmic reticulum and by taking advantage of the 1:1 stoichiometry of Ca2+ and Pi transport into the sarcoplasmic reticulum lumen during Ca-Pi precipitation-induced Ca2+ loading. The apparent rate of Pi entry into the sarcoplasmic reticulum increased with increasing myoplasmic [Pi] in the 10 mM-50 mM range at a fixed, resting myoplasmic pCa of 7.15, as judged by the increase in the rate of Ca-Pi precipitation-induced sarcoplasmic reticulum Ca2+ uptake. At 20 mM myoplasmic [Pi] the rate of Pi entry was calculated to be at least 51 microM s-1 while the amount of Pi loaded appeared to saturate at around 3.5 mM (per fibre volume). These values are approximations due to the complex kinetics of formation of different species of Ca-Pi precipitate formed under physiological conditions. Phenylphosphonic acid (PhPA, 2.5 mM) inhibited Pi transport by 37% at myoplasmic pCa 6.5 and also had a small, direct inhibitory effect on the sarcoplasmic reticulum Ca2+ pump (16%). In contrast, phosphonoformic acid (PFA, 1 mM) appeared to enhance both the degree of Pi entry and the activity of the sarcoplasmic reticulum Ca2+ pump, results that were attributed to transport of PFA into the sarcoplasmic reticulum lumen and its subsequent complexation with Ca2+. Thus, results from these studies indicate the presence of a Pi transporter in the sarcoplasmic reticulum membrane of mammalian skeletal muscle fibres that is (1) active at physiological concentrations of myoplasmic Pi and Ca2+ and (2) partially inhibited by PhPA. This Pi transporter represents a link between changes in myoplasmic [Pi] and subsequent changes in sarcoplasmic reticulum luminal [Pi]. It might therefore play a role in the delayed metabolic impairment of sarcoplasmic reticulum Ca2+ release seen during muscle fatigue, which should occur abruptly once the Ca-Pi solubility product is exceeded in the sarcoplasmic reticulum lumen.
Animals↗
Effects of 2,5-di-tert-butylhydroquinone on rat cardiac muscle contractility.
The effects of 2,5-di-tert-butylhydroquinone (TBQ) on cardiac muscle contractility were investigated using cardiac preparations from the right ventricle of the rat. In saponin-skinned preparations, TBQ (50 and 100 microM) did not significantly affect the maximal isometric Ca2+-activated force or the steady-state force-Ca2+ concentration relation but significantly reduced the Ca2+ content of the sarcoplasmic reticulum (SR) in both the absence and the presence of 50 microM of the SR Ca2+-release channel blocker ruthenium red. The effect of TBQ on SR Ca2+ content was not due to an increased passive Ca2+ leak or Ca2+-induced Ca2+ release from the SR but to the specific inhibition of the SR Ca2+ pump. In electrically stimulated (0.2 Hz, 23 degrees C) intact cardiac preparations loaded with the Ca2+-sensitive fluorescent dye fura 2, TBQ (50 and 100 microM) caused the decrease in the rates of rise and fall of the fura 2 signal (ratio of fluorescence intensities at 360- and 380-nm excitation) and isometric force. In the presence of 50 and 100 microM TBQ, the twitch height of the isometric force response was significantly decreased, whereas the peak of the fura 2 signal was not significantly affected. At 2-Hz stimulation frequency, both parameters were reduced in the presence of 50 and 100 microM TBQ. Taken together, the results obtained in this study show that TBQ inhibits rather specifically the SR Ca2+ uptake in the rat ventricle and that it can be used as a tool to determine the function of the SR under different conditions.
Animals↗
Ca2+ handling by rat myocardium exposed to ATP solutions of different [Ca2+] and Ca2+ buffering capacity.
Cardiac preparations from the right ventricular wall of rats were exposed to ATP-containing solutions of different Ca2+ concentrations ([Ca2+]) and Ca2+ buffering capacity to determine whether such treatments affected the Ca2+ handling properties of the cardiac muscle. Exposure to 8 mM extracellular ATP (ATP0) elicited sustained, near-maximal contractures that were due to Ca2+ entry from the extracellular environment and severely diminished cardiac excitability in a partially reversible manner. At 1 mM ATP0, there was a sustained rise in diastolic force and intracellular [Ca2+] and a marked, partially reversible change in the stimulation-induced Ca2+ transients measured with fura 2. A large, transient contracture was also observed when the intact ventricular preparations were transferred from the normal physiological solution to an ATP-containing (8 mM) relaxing solution (ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid < or = 0.2 mM, < 10 nM Ca2+) with or without saponin (50 micrograms/ml). The ATP0-induced contractures were dependent on the prevalent conditions with respect to [Ca2+] and Ca2+ buffering capacity of the solutions and were associated with heavy Ca2+ loading of the sarcoplasmic reticulum (SR) and mitochondria, a less leaky SR, and a reduced SR sensitivity to the SR Ca2+ pump blocker 2,5-di-tert-butyl hydroquinone. The results indicate that the Ca2+ handling properties and the electrical excitability of ventricular preparations can be markedly modified by exposure to ATP0 and that conditions prevalent during skinning with saponin are important in determining the properties of the intracellular Ca2+ stores.
Adenosine Triphosphate↗
Oxidation effects in fatigue: unphysiological responses to "depolarization" in skinned muscle fibers.
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Animals↗