scholarly journals Patterns of sarcomere activation, temperature dependence, and effect of ryanodine in chemically skinned cardiac fibers.

1986 ◽  
Vol 87 (6) ◽  
pp. 885-905 ◽  
Author(s):  
A Lundblad ◽  
H Gonzalez-Serratos ◽  
G Inesi ◽  
J Swanson ◽  
P Paolini
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Temperature Dependence ◽  
Calcium Release ◽  
Contractile Activity ◽  
The Other ◽  
Calcium Blockers ◽  
Calcium Accumulation ◽  
Contractile Activation

Functionally skinned and electrochemically shunted myocytes were prepared by perfusing rat hearts with collagenase in order to obtain a technically improved measurement of sarcomere dynamics and to evaluate the role of sarcoplasmic reticulum in situ with respect to contractile activation. In the presence of micromolar calcium, the myocytes exhibited phasic and propagated contraction waves beginning at one end and proceeding along the myocyte. Beating rates, the propagation velocity of the activation wave, and single sarcomere shortening and relaxation velocities were obtained by manual or automated analysis of 16-mm film recorded at 170 frames/s from a camera attached to a microscope that was equipped with a temperature-controlled stage. In parallel experiments, calcium accumulation by the sarcoplasmic reticulum of the myocytes in situ was measured by direct isotopic tracer methods. The frequency (10-38 min-1) of spontaneous contractions, the velocity (1.9-7.4 microns . s-1) of sarcomere shortening, and the velocity (1.7-6.8 microns . s-1) of sarcomere relaxation displayed identical temperature dependences (Q10 = 2.2), which are similar to that of the calcium pump of sarcoplasmic reticulum and are consistent with a rate limit imposed by enzyme-catalyzed mechanisms on all these parameters. On the other hand, the velocity (77-159 microns . s-1) of sequential sarcomere activation displayed a lower temperature dependence (Q10 = 1.5), which is consistent with a diffusion-limited and self-propagating release of calcium from one sarcomere to the other. The phasic contractile activity of the dissociated myocytes was inhibited by 10(-8)-10(6) M ryanodine (and not by myolemmal calcium blockers) under conditions in which calcium accumulation by sarcoplasmic reticulum in situ was demonstrated to proceed optimally. The effect of ryanodine is attributed to an interaction of this drug with sarcotubular structures, producing inhibition of calcium release from the sarcoplasmic reticulum. The consequent lack of sarcomere activation underlines the role of sarcoplasmic reticulum uptake and release in the phasic contractile activation of the electrochemically shunted myocytes.

The Sarcoplasmic Reticulum in Muscle Fatigue and Disease: Role of the Sarco(endo)plasmic Reticulum Ca2+-ATPase

2004 ◽  
Vol 29 (3) ◽  
pp. 308-329 ◽  
Author(s):  
A. Russell Tupling
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Release ◽  
Contractile Activity ◽  
Muscle Relaxation ◽  
Low Frequency ◽  
Free Calcium ◽  
Cellular Mechanisms ◽  
Plasmic Reticulum ◽  
Low Frequency Fatigue

Skeletal muscles induced to contract repeatedly respond with a progressive loss in their ability to generate a target force or power. This condition is known simply as fatigue. Commonly, fatigue may persist for prolonged periods of time, particularly at low activation frequencies, which is called low-frequency fatigue. Failure to activate the contractile apparatus with the appropriate intracellular free calcium ([Ca2+]f) signal contributes to fatigue but the precise mechanisms involved are unknown. The sarcoplasmic reticulum (SR) is the major organelle in muscle that is responsible for the regulation of [Ca2+]f, and numerous studies have shown that SR function, both Ca2+ release and Ca2+ uptake, is impaired following fatiguing contractile activity. The major aim of this review is to provide insight into the various cellular mechanisms underlying the alterations in SR Ca2+ cycling and cytosolic [Ca2+]f that are associated both with the development of fatigue during repeated muscle contraction and with low-frequency or long-lasting fatigue. The primary focus will be on the role of the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) in normal muscle function, fatigue, and disease. Key words: calcium release, calcium uptake, muscle relaxation, low-frequency fatigue, Brody disease

scholarly journals Primary role of sarcoplasmic reticulum in phasic contractile activation of cardiac myocytes with shunted myolemma.

1981 ◽  
Vol 91 (3) ◽  
pp. 728-742 ◽  
Author(s):  
M Chiesi ◽  
M M Ho ◽  
G Inesi ◽  
A V Somlyo ◽  
A P Somlyo
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Electron Probe ◽  
Calcium Release ◽  
Contractile Activity ◽  
Heart Cells ◽  
Primary Role ◽  
Electron Probe Analysis ◽  
Ca Transport ◽  
Probe Analysis ◽  
Contractile Activation

Homogeneous populations of single myocytes showing good preservation of ultrastructure were obtained by enzymatic digestion of rabbit and rat hearts, and maintained in a relaxed state in the presence of free Ca2+ concentrations less than 10(-7) M. Ultrastructural details such as a cytoskeleton of 100-A filaments connected to the sarcolemma at the Z lines were demonstrated especially well in these preparations. In spite of seemingly normal structure, electron probe analysis of cryosections reveals similar concentrations of electrolytes in the medium and in the cytoplasm, indicating the presence of electrochemical shunting across the external membrane. The dissociated myocytes display Ca uptake and phasic contractions that are apparently dependent on mitochondrial respiration, but are not affected by mitochondrial uncouplers when ATP and phosphocreatine are added. The uptake is augmented by oxalate and, based on identification of calcium oxalate crystals by electron microscopy and electron probe analysis, is localized to the sarcoplasmic reticulum (SR). An advantageous feature of the dissociated myocytes is that they are suitable for experiments using large numbers of cells in suspension. Thereby, velocities of calcium transport were measured directly by isotopic tracer and filtration methods. It was then found that the lowest CA2+ concentrations (5 x 10(-7) M for the rabbit and 1 x 10(-7) M for the rat) sustaining Ca transport also induce phasic contractile activity in all myocytes, even though the external membrane is electrochemically shunted. A stepwise rise in the Ca2+ concentration of up to one order of magnitude, increases transport velocities in parallel with the rates of phasic contractions. Both these parameters are affected by Mg2+, temperature, cyclic-AMP, and methylxanthines, even though the Ca2+ concentration is maintained constant in the medium. Therefore, Ca transport by SR is a requirement and a rate limiting factor for the occurrence of phasic contractile activation in dissociated cardiac cells retaining an electrochemically shunted external membrane. It is suggested that transient Ca release required for phasic contractile activation is due to equilibrium oscillations across the SR membrane. The sequential pattern of sarcomere activation is consistent with a self propagating mechanism of calcium release. SR in dissociated skeletal muscle cells sustains a greater Ca transport activity than in dissociated heart cells. However, the heart cells display a much higher phasic contractile activity, indicating that cardiac SR has a greater tendency to release accumulated calcium. If free Ca2+ in the medium is raised above 10(-6) M, both cardiac and skeletal myocytes undergo contractures and degenerative phenomena, accompanied by Ca, Mg, and phosphate accumulation in cardiac mitochondria.

scholarly journals The Effect of Calcium Ionophores on Fragmented Sarcoplasmic Reticulum

1972 ◽  
Vol 60 (6) ◽  
pp. 735-749 ◽  
Author(s):  
Antonio Scarpa ◽  
Judith Baldassare ◽  
Giuseppe Inesi
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Binding ◽  
Calcium Release ◽  
Atp Hydrolysis ◽  
Divalent Cations ◽  
Electron Microscopic ◽  
Microscopic Appearance ◽  
Calcium Accumulation ◽  
Calcium Dependent ◽  
Dependent Atpase

X-537 A and A 23187, two antibiotics which form liphophilic complexes with divalent cations, function as ionophores in vesicular fragments of sarcoplasmic reticulum (SR). Addition of either ionophore to SR preloaded with calcium in the presence of adenosine triphosphate (ATP), causes rapid release of calcium. Furthermore, net calcium accumulation by SR is prevented, when the ionophores are added to the reaction mixture before ATP. On the contrary, ATP-independent calcium binding to SR is not inhibited. This effect is specific for the two antibiotics and could not be reproduced, either by inactive derivatives, or by other known ionophores. Neither ionophore produces alterations of the electron microscopic appearance of SR membranes or inhibition of the calcium-dependent ATPase. In fact, the burst of ATP hydrolysis obtained on addition of calcium, is prolonged in the presence of the ionophores. Lanthanum inhibits ATP-independent calcium binding to SR, ATP-dependent calcium accumulation and calcium-dependent ATPase. However, addition of lanthanum to SR preloaded in the presence of ATP, does not cause calcium release. The reported experiments indicated that: (a) ATP-dependent calcium accumulation by SR results in primary formation of calcium ion gradients across the membrane. (b) Most of the accumulated calcium is not available for displacement by lanthanum on the outer surface of the membrane. (c) Calcium ionophores induce rapid equilibration of the gradients, by facilitating cation diffusion across the membrane.

Postulated role of calsequestrin in the regulation of calcium release from sarcoplasmic reticulum

Biochemistry ◽  
1989 ◽  
Vol 28 (16) ◽  
pp. 6764-6771 ◽  
Author(s):  
Noriaki Ikemoto ◽  
Michel Ronjat ◽  
Laszlo G. Meszaros ◽  
Makoto Koshita
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Release

Pacemaker activity in the insect (T. molitor) heart: role of the sarcoplasmic reticulum

2011 ◽  
Vol 301 (6) ◽  
pp. R1838-R1845 ◽  
Author(s):  
Danielle F. Feliciano ◽  
Rosana A. Bassani ◽  
Pedro X. Oliveira ◽  
José W. M. Bassani
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Cells ◽  
Pacemaker Activity ◽  
Electrophysiological Properties ◽  
Chronotropic Response ◽  
Different Types ◽  
Mealworm Beetle ◽  
Beating Rate

The electrophysiological properties of the myogenic cardiac cells of insects have been analyzed, but the mechanisms that regulate the pacemaker activity have not been elucidated yet. In mammalian pacemaker cells, different types of membrane ion channels seem to be sequentially activated, perhaps in a cooperative fashion with the current generated by Ca2+ extrusion mediated by the electrogenic Na+/Ca2+ exchanger, which is sustained by the diastolic sarcoplasmic reticulum (SR) Ca2+ release. The objective of the present work was to investigate the role of the SR function on the basal beating rate (BR), and BR modulation by extracellular Ca2+ concentration ([Ca2+]o) and neurotransmitters in the in situ dorsal vessel (heart) of the mealworm beetle Tenebrio molitor . The main observations were as follows: 1) basal BR was reduced by 50% by inhibition of SR function, but not affected by perfusion with CsCl or ZD7288; 2) spontaneous activity was abolished by Cd2+; 3) a robust positive chronotropic response could be elicited to serotonin (5-HT), but not to norepinephrine or carbamylcholine; 4) SR inhibition abolished the sustained chronotropic stimulation by [Ca2+]o elevation and by 5-HT, while the latter was unaffected by CsCl. It is concluded that, in T. molitor heart, BR is markedly, but not exclusively, dependent on the SR function, and that BR control and modulation by both [Ca2+]o and 5-HT requires a functional SR.

Ruthenium red selectively prevents Ins(1,4,5)P3-but not caffeine-gated calcium release in avian atrium

1992 ◽  
Vol 262 (1) ◽  
pp. H268-H277 ◽  
Author(s):  
A. M. Vites ◽  
A. J. Pappano
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Release ◽  
Present Report ◽  
Ruthenium Red ◽  
Detectable Effect ◽  
Calcium Accumulation ◽  
Two Agents ◽  
Release Mechanisms ◽  
Subsequent Response ◽  
Inositol 1,4,5 Trisphosphate

We previously reported that inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and caffeine evoked contractures in saponin-permeabilized chick atria. The magnitude of contractures evoked by maximally effective concentrations of Ins(1,4,5)P3 were half those evoked by maximally effective concentrations of caffeine. In the present report, we tested the hypothesis that these two agents may act on distinct calcium-release mechanisms by comparing the effects of ryanodine, ruthenium red, and procaine on the responses to Ins(1,4,5)P3 and caffeine. We find that procaine inhibits both responses with similar mean inhibitory concentrations in the millimolar range. Nanomolar concentrations of ryanodine selectively potentiate the contractures induced by Ins(1,4,5)P3 but have no effect on those induced by caffeine. Micromolar concentrations of ryanodine inhibit responses to both Ins(1,4,5)P3 and caffeine in a use-dependent way. Ruthenium red prevents the response to Ins(1,4,5)P3 and potentiates that to caffeine, as if ruthenium red had enhanced calcium accumulation in the caffeine-sensitive pool(s). Because we found that caffeine prevented the subsequent response to Ins(1,4,5)P3, but Ins(1,4,5)P3 had no detectable effect on the caffeine-induced contracture, we conclude that Ins(1,4,5)P3 and caffeine act on pharmacologically distinct calcium-release mechanisms that may reside in the same sarcoplasmic reticulum compartment.

Biochemistry and Morphology of Fragmented Sarcoplasmic Reticulum

1970 ◽  
Vol 28 ◽  
pp. 90-91 ◽  
Author(s):  
J. B. Peter ◽  
W. Fiehn ◽  
Robert F. Dunn
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Guinea Pig ◽  
Relaxation Cycle ◽  
Calcium Accumulation ◽  
Maximal Amount ◽  
Slow Twitch ◽  
Vesicle Protein ◽  
Fast Twitch ◽  
Kinetics Of

The function of the sarcoplasmic reticulum (SR) is well defined, but much confusion exists about the role of the SR in the contraction-relaxation cycle of slow-twitch muscles. Fragmented SR (FSR) was isolated from different guinea pig muscles. The muscles were classified as fast-twitch-red, fast-twitch-white or slow-twitch-intermediate according to their contractionrelaxation times and the histochemical characteristics of the component fibers.The kinetics of calcium accumulation showed no difference between FSR from fast-twitch-red or fast-twitch-white muscles, and the yield of FSR (expressed as mg vesicle protein per gram of muscle) was the same. By contrast the amount of FSR obtained per gram of slow-twitch-intermediate muscle was only half as high. Likewise, the maximal amount of calcium that could be stored in the presence of oxalate by FSR from slow-twitch-intermediate muscles was only half that of FSR from fast-twitch muscles.

Ontogeny of neuropeptide Y expression in response to deprivation in lean Zucker rat pups

1998 ◽  
Vol 275 (2) ◽  
pp. R466-R470 ◽  
Author(s):  
Timothy J. Kowalski ◽  
Thomas A. Houpt ◽  
Jeongwon Jahng ◽  
Nori Okada ◽  
Streamson C. Chua ◽  
...  
Keyword(s):  
In Situ Hybridization ◽  
Neuropeptide Y ◽  
Arcuate Nucleus ◽  
Maternal Deprivation ◽  
The Other ◽  
Zucker Rat ◽  
Adult Rats ◽  
Rat Pups

Hypothalamic neuropeptide Y (NPY) activity is believed to play an important role in the response to food deprivation in adult rats. Little is known, however, about the role of the hypothalamic NPY system in the control of food intake in the preweanling rat. To address this issue, we examined the effect of deprivation on arcuate nucleus preproNPY expression in lean Zucker rat pups, using in situ hybridization. PreproNPY expression within the arcuate nucleus was localized to cells in the medial portion. Twenty-four hours of food, water, and maternal deprivation significantly increased the relative abundance of preproNPY mRNA in pups on postnatal day (P) 2, P9, P12, and P15 by 14–31%. This response, however, was not observed on P5. The absence of an effect on P5 and the magnitude of the response at the other ages tested were not correlated with the amount of weight lost during deprivation.

scholarly journals The Role of Prosody in the Identification of Persian Sentence Types: Declarative or Wh-question?

2017 ◽  
Vol 3 (1) ◽  
Author(s):  
Zohreh Shiamizadeh ◽  
Johanneke Caspers ◽  
Niels O. Schiller
Keyword(s):  
Native Speakers ◽  
Sentence Type ◽  
Initial Position ◽  
The Other ◽  
Current Experiment ◽  
Frequency Code ◽  
Other Hand ◽  
The One

AbstractIt has been reported that prosody contributes to the identification of utterances which lack lexico-syntactic indicators of interrogativity but do have characteristic prosodic correlates (e.g. Vion and Colas 2006. Pitch cues for the recognition of yes-no questions in French. Journal of Psycholinguistics Research 35. 427–445). In Persian wh-in-situ questions, the interrogativity device (the wh-phrase) does not move to the sentence-initial position, and the pre-wh part is characterized by specific prosodic correlates (Shiamizadeh et al. 2016. Do Persian native speakers prosodically mark wh-in-situ questions? Manuscript submitted for publication). The current experiment investigates the role of prosody in the perception of Persian wh-in-situ questions as opposed to declaratives. To this end, an experiment was designed in which Persian native speakers were asked to choose the correct sentence type after hearing only the pre-wh part of a sentence. We hypothesized that prosody guides perception of wh-in-situ questions independent of wh-phrase type. The results of the experiment corroborate our hypothesis. The outcome is discussed in terms of Ohala´s frequency code, and Bolinger´s claim about the universal dichotomous association between relaxation and declarativity on the one hand and tension and interrogativity on the other hand.

Sign in / Sign up

Export Citation Format

Share Document