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1.
Summary The trigger calcium hypothesis of signal transmission between T-tubules and terminal cisternae (TC) of the sarcoplasmic reticulum (SR) in twitch muscle fibres implies the presence of calcium along T-tubule membranes at rest and its release upon excitation. To test this hypothesis, calcium was immobilised using a fixing and precipitating solution of glutaraldehyde in phosphate buffer at pH 8.0 and the calcium was substituted for by lead. Simultancous tension recordings revealed the occurence of contra tions or a burst of twitches upon perfusion with the tixative. Procaine or tetrodotoxin (TTX) was used to inhibit this activity. In fibres without fixative-induced activity, precipitates were observed along T-tubules and in adjoining parts of TC. In activated fibres, tubular and TC precipitates were absent. These results are consistent with the trigger calcium hypothesis. In fibres activated by depolarisation, calcium returned to TC after passing successively through different parts of the SR. 相似文献
2.
M A Bagni G Cecchi B Colombini F Colomo 《Journal of electromyography and kinesiology》1999,9(2):77-86
Data reported in the literature suggest that crossbridges in rapid equilibrium between attached and detached states (weakly binding bridges), demonstrated in relaxed skinned fibres at low ionic strength, could be present also in intact fibres under physiological conditions. In addition, it was suggested that the well known leading of stiffness over force during the tension development in stimulated muscle fibres could be due to an increased number of weakly binding bridges induced by the stimulation. The experiments reviewed in this paper were made to investigate these possibilities. Fast ramp length changes were applied to single frog muscle fibres at rest and during the early phases of activation. The corresponding force changes were analysed, searching for the components expected from the presence of weakly binding bridges. The results showed no mechanical indication for the presence of weakly binding bridges in both skinned and intact fibres, either at rest or during activation. It was also found that a portion of the fibre stiffness increase induced by stimulation leads the formation of crossbridges. 相似文献
3.
Minimal latency of calcium release in frog twitch muscle fibres 总被引:3,自引:0,他引:3
P H Zhu I Parker R Miledi 《Proceedings of the Royal Society of London. Series B, Containing papers of a Biological character. Royal Society (Great Britain)》1986,229(1254):39-46
Intracellular release of calcium in frog skeletal muscle fibres was monitored by the use of arsenazo III, in response to voltage clamped depolarizing pulses. A latency of a few milliseconds was evident between the onset of depolarization and the first detectable rise in the arsenazo-calcium signal, and this decreased logarithmically as the depolarization was increased. The minimal latency with strong depolarization (to +20 to +100 mV) was about 2 ms at 5 degrees C. This delay appears to be sufficiently long to be compatible with a chemically mediated coupling mechanism between depolarization and calcium release from the sarcoplasmic reticulum. 相似文献
4.
K W Snowdowne 《Biochimica et biophysica acta》1986,862(2):441-444
The concentration of free calcium in the sarcoplasm of a resting frog skeletal muscle is increased by stretch. The magnitude of the rise in free calcium increased with the degree of stretch and the ambient temperature and it was enhanced by caffeine. This phenomenon might play a role in the twitch potentiation and enhanced metabolic rate evoked by stretch. 相似文献
5.
Reduction of calcium inactivation of sarcoplasmic reticulum calcium release by fura-2 in voltage-clamped cut twitch fibers from frog muscle 总被引:9,自引:3,他引:9
《The Journal of general physiology》1993,102(2):333-370
Cut fibers from Rana temporaria and Rana pipiens (striation spacing, 3.9-4.2 microns) were mounted in a double Vaseline-gap chamber and studied at 14 degrees C. The Ca indicator purpurate-3,3' diacetic acid (PDAA) was introduced into the end pools and allowed to diffuse into the optical recording site. When the concentration at the site exceeded 2 mM, step depolarizations to 10 mV were applied and the [Ca] transient measured with PDAA was used to estimate Ca release from the sarcoplasmic reticulum (SR) (Baylor, S. M., W. K. Chandler, and M. W. Marshall. 1983. Journal of Physiology. 344:625-666). With depolarization, the rate of SR Ca release increased to an early peak and then rapidly decreased several-fold to a quasi-steady level. The total amount of Ca released from the SR at the time of peak rate of release appeared to be independent of SR Ca content, consistent with the idea that a single activated channel might pass, on average, a fixed number of ions, independent of the magnitude of the single channel flux. A possible explanation of this property is given in terms of locally induced Ca inactivation of Ca release. The solution in the end pools was then changed to one with PDAA plus fura-2. SR Ca release was estimated from the [Ca] transient, as before, and from the delta [Cafura-2] signal. On average, 2-3 mM fura-2 increased the quasi-steady level of the rate of SR Ca release by factors of 6.6 and 3.8, respectively, in three fibers from Rana temporaria and three fibers from Rana pipiens. The peak rate of release was increased in five of the six fibers but to a lesser extent than the quasi-steady level. In all fibers, the amplitude of the free [Ca] transient was markedly reduced. These increases in the rate of SR Ca release are consistent with the idea that Ca inactivation of Ca release develops during a step depolarization to 10 mV and that 2-3 mM fura-2 is able to reduce this inactivation by complexing Ca and thereby reducing free [Ca]. Once the concentration of fura-2 becomes sufficiently large, a further increase reduces the rate of SR Ca release. On average, 5-6 mM fura-2 increased the quasi-steady rate of release, compared with 0 mM fura-2, by 6.5 and 2.9, respectively, in four fibers from Rana temporaria and three from Rana pipiens.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
6.
7.
Summary In white muscle fibres of a teleost fish T-tubule openings may occur regularly at all Z-disc levels between adjacent peripheral myofibrils, the T-tubule openings thus occurring at a density of ca. 0.9 m-2.In frog white fibres, T-tubule openings are infrequently seen in material fixed like the fish material. In material prepared according to the albumin method of Gray (1975, 1976 a, b) which renders the muscle fibres swollen, straight tubules or sometimes chains of vesicles instead are seen opening at the sarcolemmal surface. Such tubules occur at a higher density than expected from experiments with local activation of contraction. Lability and dynamics within the T-system normally and during fixation are discussed. 相似文献
8.
Mechanically skinned skeletal muscle fibres of the crab Carcinus maenas have been used to investigate the mechanism of calcium release from the sarcoplasmic reticulum. Calcium release has been monitored by the amplitude and kinetics of the tension developed by the fibre. Results show that a very low calcium concentration, insufficient to directly activate contractile proteins, induces a release of calcium from the SR. This release is stimulated by low concentrations of caffeine and inhibited by small amounts of EGTA. Thus, a graded calcium-induced calcium release mechanism dependent on extrareticular calcium concentration has been demonstrated in skinned crab muscle fibre. 相似文献
9.
10.
Sarcoplasmic and myofibrillar proteins of a frog mixed muscle (distal cruralis bundle) were investigated and compared to their fast twitch muscle homologues. Histochemical reactions revealed two populations of fibres in this muscle, differing from fast twitch fibres by the intensity of their myofibrillar ATPase reaction and by their mitochondrial NADH dehydrogenase activity. The distribution of parvalbumins and LDH isoenzymes in the whole muscle showed some features of tonic muscle type. Myosin light chains pattern of cruralis bundle fibres was characterized by the lower proportion of the LC3 subunit. These results confirmed the heterogeneity of this frog muscle and the presence of tonic or intermediate fibres with their typical sarcoplasmic and myofibrillar proteinic composition. 相似文献
11.
A slow component of intramembranous charge movement during sarcoplasmic reticulum calcium release in frog cut muscle fibers 总被引:6,自引:1,他引:6 下载免费PDF全文
《The Journal of general physiology》1996,107(1):79-101
Cut muscle fibers from Rana temporaria were mounted in a double Vaseline-gap chamber and equilibrated with an end-pool solution that contained 20 mM EGTA and 1.76 mM Ca (sarcomere length, 3.3-3.8 microns; temperature, 14-16 degrees C). Sarcoplasmic reticulum (SR) Ca release, delta[CaT], was estimated from changes in myoplasmic pH (Pape, P.C., D.- S. Jong, and W.K. Chandler. 1995. J. Gen. Physiol. 106:259-336). The maximal value of delta[CaT] obtained during a depleting depolarization was assumed to equal the SR Ca content before stimulation, [CaSR]R (expressed as myoplasmic concentration). After a depolarization to -55 to -40 mV in fibers with [CaSR]R = 1,000-3,000 microM, currents from intramembranous charge movement, Icm, showed an early I beta component. This was followed by an I gamma hump, which decayed within 50 ms to a small current that was maintained for as long as 500 ms. This slow current was probably a component of Icm because the amount of OFF charge, measured after depolarizations of different durations, increased according to the amount of ON charge. Icm was also measured after the SR had been depleted of most of its Ca, either by a depleting conditioning depolarization or by Ca removal from the end pools followed by a series of depleting depolarizations. The early I beta component was essentially unchanged by Ca depletion, the I gamma hump was increased (for [CaSR]R > 200 microM), the slow component was eliminated, and the total amount of OFF charge was essentially unchanged. These results suggest that the slow component of ON Icm is not movement of a new species of charge but is probably movement of Q gamma that is slowed by SR Ca release or some associated event such as the accompanying increase in myoplasmic free [Ca] that is expected to occur near the Ca release sites. The peak value of the apparent rate constant associated with this current, 2-4%/ms at pulse potentials between -48 and -40 mV, is decreased by half when [CaSR]R approximately equal to 500-1,000 microM, which gives a peak rate of SR Ca release of approximately 5-10 microM/ms. 相似文献
12.
Synthesis of polyphosphoinositides has been studied in transverse (T-) tubule and sarcoplasmic reticulum (SR) membrane fractions of frog skeletal muscle, following 32P-labeling with [gamma-32P]ATP. Purified SR and T-tubule fractions respectively synthesize 9.4 +/- 0.8 and 71.9 +/- 9.8 pmol PtdInsP/mg per min, indicating nearly 8-fold higher activity of PtdIns kinase in the T-tubules than in the SR. The activity of this enzyme in both membrane systems is maximum at pH 7 and pCa 6. PtdInsP2 is synthesized from the endogenous PtdInsP, only in T-tubule membranes by the action of PtdInsP kinase. This lipid is the most intensely 32P-labeled phosphoinositide (181.7 +/- 9.2 pmol/mg per min) in these membranes. PtdIns kinase in the T-tubule and SR membranes, and PtdInsP kinase in the former are modulated by the free [Mg2+]. Loss of radiolabel from transiently maximal 32P-incorporation in polyphosphoinositides in T-tubule membranes, concomitant with a decrease in the ATP concentration in the incubation buffer, shows the occurrence of phosphoinositidases in these membranes. Under the conditions used, no such activities were evident in SR membranes. Compound 48/80, a mixture of condensation products of N-methyl-p-methoxyphenethylamine with formaldehyde, known to block phosphoinositidase C and phospholipase A2, causes a dose-dependent increase in the 32P-label of PtdInsP, in T-tubule membranes. The synthesis of lyso PtdInsP2, a deacylated form of PtdInsP2 which occurs in nearly equal quantities in both T-tubule and SR membranes, may result from a mechanism independent of phospholipase A2. 相似文献
13.
Effect of sarcoplasmic reticulum calcium depletion on intramembranous charge movement in frog cut muscle fibers 总被引:5,自引:2,他引:5
《The Journal of general physiology》1995,106(4):659-704
Cut muscle fibers from Rana temporaria (sarcomere length, 3.3-3.5 microns; temperature, 13-16 degrees C) were mounted in a double Vaseline-gap chamber and equilibrated for at least an hour with an internal solution that contained 20 mM EGTA and phenol red and an external solution that contained predominantly TEA-gluconate; both solutions were nominally Ca-free. The increase in total myoplasmic concentration of Ca (delta[CaT]) produced by sarcoplasmic reticulum (SR) Ca release was estimated from the change in pH produced when the released Ca was complexed by EGTA (Pape, P.C., D.-S. Jong, and W.K. Chandler. 1995. Journal of General Physiology. 106:259-336). The resting value of SR Ca content, [CaSR]R (expressed as myoplasmic concentration), was taken to be equal to the value of delta[CaT] obtained during a step depolarization (usually to -50 to -40 mV) that was sufficiently long (200-750 ms) to release all of the readily releasable Ca from the SR. In ten fibers, the first depolarization gave [CaSR]R = 839-1,698 microM. Progressively smaller values were obtained with subsequent depolarizations until, after 30-40 depolarizations, the value of [CaSR]R had usually been reduced to < 10 microM. Measurements of intramembranous charge movement, Icm, showed that, as the value of [CaSR]R decreased, ON-OFF charge equality held and the amount of charge moved remained constant. ON Icm showed brief initial I beta components and prominent I gamma "humps", even after the value of [CaSR]R was < 10 microM. Although the amplitude of the hump component decreased during depletion, its duration increased in a manner that preserved the constancy of ON charge. In the depleted state, charge movement was steeply voltage dependent, with a mean value of 7.2 mV for the Boltzmann factor k. These and other results are not consistent with the idea that there is one type of charge, Q beta, and that I gamma is a movement of Q beta caused by SR Ca release, as proposed by Pizarro, Csernoch, Uribe, Rodriguez, and Rios (1991. Journal of General Physiology. 97:913-947). Rather, our results imply that Q beta and Q gamma represent either two distinct species of charge or two transitions with different properties of a single species of charge, and that SR Ca content or release or some related event alters the kinetics, but not the amount of Q gamma. Many of the properties of Q gamma, as well as the voltage dependence of the rate of SR Ca release for small depolarizations, are consistent with predictions from a simple model in which the voltage sensor for SR Ca release consists of four interacting charge movement particles. 相似文献
14.
15.
R. J. Baskin 《Journal of bioenergetics and biomembranes》1972,3(3-4):249-269
Vesicles of fragmented sarcoplasmic reticulum membranes have been adsorbed on to 2.68 latex spheres. Observation of these vesicle containing spheres in the presence of an electric field allows a calculation of the electrophoretic mobility of the vesicles Following this determination, the net membrane surface charge has been estimated. The mobility of sarcoplasmic reticulum membranes exhibited a dependency on pH. At an ionic strength of 0.10 a mobility (pH=7.0) of –0.67±0.10/sec/volt/cm was observed. At pH=7.0 and /2=0.150 the net excess negative charge density was 2.0×10–2 coul/m2. This is equivalent to one charge per 103 A2 (assuming a uniform charge distribution). With an average vesicle volume of 2.8×108 A3 and a surface area of 2×106 A2 the surface of one vesicle would contain a net of approximately 2×103 negative charges. While the mobility did not change during uptake of calcium by the vesicles, both glutaraldehyde fixation and lecithin extraction by phospholipase C greatly altered the mobility of the vesicle membrane. Calcium binding and uptake both exhibited a dependence on pH. 相似文献
16.
Summary The three-dimensional structure of the mitochondria and sarcoplasmic reticulum (SR) in the three types of twitch fibers, i.e., the red, white and intermediate skeletal muscle fibers, of the vastus lateralis muscle of the Japanese meadow frog (Rana nigromaculata nigromaculata Hallowell) was examined by high resolution scanning electron microscopy, after removal of the cytoplasmic matrices.The small red fibers have numerous mitochondrial columns of large diameter, while the large white fibers have a small number of mitochondrial columns of small diameter. In the medium-size intermediate fibers, the number and diameter of the mitochondrial columns are intermediate between those of the red and white fibers.In all three types of fibers, the terminal cisternae and transverse tubules form triads at the level of each Z-line. The thick terminal cisternae continue into much thinner flat intermediate cisternae, through a transitional part where a row of tiny indentations can be observed. Numerous slender longitudinal tubules originating from the intermediate cisternae, extend longitudinally or obliquely and form elongated oval networks of various sizes in front of the A-band, then fuse to form the H-band collar (fenestrated collar) around the myofibrils. On the surface of the H-band collar, small fenestrations as well as tiny hollows are seen. The three-dimensional structure of SR is basically the same in all three muscle fiber-types. However, the SR is sparse on the surface of mitochondria, so the mitochondria-rich red fiber has a smaller total volume of SR than the mitochondria-poor white fiber. The volume of SR of the intermediate fiber is intermediate between other the two. 相似文献
17.
Karine Fénelon Cédric R.H. Lamboley Nicole Carrier Paul C. Pape 《The Journal of general physiology》2012,140(4):403-419
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. 相似文献
18.
Proton movements across the membranes of sarcoplasmic reticulum during the uptake of calcium ions 总被引:2,自引:0,他引:2
V M Madeira 《Archives of biochemistry and biophysics》1980,200(2):319-325
A burst of proton ejection was observed during the initial steps of Ca2+ uptake by sarcoplasmic reticulum vesicles. The initial rate of this proton ejection is considerably higher than the initial rate of Ca2+ uptake, and is independent of the amount of accumulated Ca2+. The ejection of protons is a transmembrane event, since it is dissipated by the ionophore X-537A, and does not occur when the ionophore is added before the initiation of the transport of Ca2+. The low proton permeability of the membranes is largely increased by X-537A. The studies of facilitated diffusion of protons in the presence of the ionophore permitted the estimation of the pH within the vesicles. A fast alkalinization occurs within the vesicles during the initial steps of Ca2+ uptake, as revealed by sequestered bromothymol blue. The change in absorbance of this dye corresponds to a change of 0.15 pH unit within the vesicles, and a maximal transmembrane ΔpH of about 0.5 may build up. Since such a gradient may not account energetically for the transmembrane gradients of Ca2+, I suggest that a transmembrane electrical potential may develop as a consequence of proton ejection. 相似文献
19.
Young Sup Lee Karol Ondrias Adam J. Duhl Barbara E. Ehrlich Do Han Kim 《The Journal of membrane biology》1991,122(2):155-163
Summary It is shown that equations developed to analyze the contributions of secondary active transport processes to symmetrical cells (Gordon, L. G. M., Macknight, A. D. C., 1991,J. Membrane Biol.
120: 139–152) can be used, with minor modifications, to analyze the steady-state membrane potential in epithelia under the unique situation of short circuiting. Only under such conditions is there a single intracellular potential relative to both the mucosal and serosal media. The equations are investigated in relation to a model tight epithelium—the toad urinary bladder. It is shown that the properties of the membrane transport pathways are such that the intracellular potential under short-circuit conditions must be more negative than often reported. Given measurements of membrane potential and of voltage-divider ratio, it is possible to use the equations to estimate the absolute values of the membrane permeabilities and conductances under shortcircuit conditions. 相似文献