scholarly journals Ca2+ homeostasis and fast-type sarcoplasmic reticulum Ca2+-ATPase expression in L6 muscle cells. Role of thyroid hormone

1992 ◽  
Vol 283 (3) ◽  
pp. 713-718 ◽  
Author(s):  
A Muller ◽  
C van Hardeveld ◽  
W S Simonides ◽  
J van Rijn
Keyword(s):  
Thyroid Hormone ◽  
Sarcoplasmic Reticulum ◽  
Resting Cells ◽  
Mediating Role ◽  
L6 Myotubes ◽  
High K ◽  
Control Myotubes ◽  
The Mean ◽  
K Concentration

The effect of thyroid hormone (L-tri-iodothyronine; T3) on the cytosolic free Ca2+ concentration ([Ca2+]i) in L6 myotubes was studied at rest and during activation to explore the possible mediating role of [Ca2+]i in the T3-induced net synthesis of fast-type sarcoplasmic reticulum (SR) Ca(2+)-ATPase. The mean [Ca2+]i at rest was approx. 115 nM in myoblasts, control myotubes and T3-treated myotubes. Therefore it is unlikely that the T3-induced elevation of Ca(2+)-ATPase levels is mediated by [Ca2+]i changes. To investigate the influence of the 4-fold higher Ca(2+)-ATPase levels in T3-treated myotubes (compared with controls) on [Ca2+]i, interventions with caffeine (10 mM) and a high extracellular K+ concentration ([K+]o) (30 mM) were applied which initially mobilize Ca2+ predominantly from the SR. The results showed a lower (caffeine) or not significantly different (high [K+]o) increase in [Ca2+]i in T3-treated myotubes compared with controls. No rise in [Ca2+]i was found in myoblasts with caffeine or high [K+]o. The role of [Ca2+]i in the regulation of Ca(2+)-ATPase levels was investigated by varying [Ca2+]i through exposure of cells to different concentrations of extracellular Ca2+ (0.2-1.8 mM) and ionomycin (0.1-0.25 microM). At subnormal [Ca2+]i (55 nM) the T3-induced net synthesis of Ca(2+)-ATPase was virtually abolished, and at supranormal [Ca2+]i (195 nM) it was greatly depressed. Intermediate stimulation of net Ca(2+)-ATPase synthesis was found at [Ca2+]i of 95 and 165 nM, with an optimum at approx. 125 nM. Similar but less pronounced effects were found for the basal Ca(2+)-ATPase levels. In contracting primary rat myotubes, Ca(2+)-ATPase levels were significantly lower than in tetrodotoxin-arrested myotubes. The same results were obtained in the presence of T3. Since the mean [Ca2+]i in contracting cells is higher than in resting cells, these data agree with those obtained in the L6 cells with ionomycin. A major conclusion of this study is the existence of a [Ca2+]i optimum, near resting levels, for the expression of the fast-type Ca(2+)-ATPase in the L6 muscle cell line.

Na+-Ca2+ exchange contributes to increase of cytosolic Ca2+ concentration during depolarization in heart muscle

1986 ◽  
Vol 250 (4) ◽  
pp. C651-C656 ◽  
Author(s):  
S. S. Sheu ◽  
V. K. Sharma ◽  
A. Uglesity
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Channel Blocker ◽  
Ventricular Myocytes ◽  
Transport Systems ◽  
High K ◽  
K Concentration ◽  
Cardiac Excitation ◽  
Ca2 Channels ◽  
Isolated Rat

The possible role of Na+-Ca2+ exchange in contributing to depolarization-induced increase in cytosolic Ca2+ concentration ([Ca2+]i) of isolated rat ventricular myocytes was investigated. Measured with the Ca2+-sensitive indicator quin 2, [Ca2+]i increased from 177 +/- 12 (mean +/- SE, n = 11) to 468 +/- 41 nM when cells were depolarized with solutions containing 50 mM KCl [high extracellular K+ concentration ([K+]o)]. Approximately 73% of this high-[K+]o-induced increase in [Ca2+]i was abolished by the Ca2+ channel blocker verapamil (5 microM). For cells pretreated with 10 mM caffeine to deplete the Ca2+ stored in sarcoplasmic reticulum, 50 mM KCl still produced an increase in [Ca2+]i, even in the presence of 5 microM verapamil. However, if extracellular Na+ was replaced by Li+ or tris(hydroxymethyl)aminomethane, this increase was completely abolished. The results suggest that, in addition to voltage-sensitive Ca2+ channels, voltage-sensitive Na+-Ca2+ exchange can also contribute to the increase in [Ca2+]i on depolarization. Therefore both Ca2+ transport systems may play important roles in regulating cardiac excitation and contraction.

K(+)-induced inhibition of contractile force in rat skeletal muscle: role of active Na(+)-K+ transport

1991 ◽  
Vol 261 (5) ◽  
pp. C799-C807 ◽  
Author(s):  
T. Clausen ◽  
M. E. Everts
Keyword(s):  
Rat Skeletal Muscle ◽  
Uniform Size ◽  
Muscle Work ◽  
Standard Buffer ◽  
High K ◽  
Longus Muscle ◽  
K Concentration ◽  
K Transport ◽  
Contractile Performance

During excitation, K+ is lost from the working muscle fibers, and interfiber K+ may reach 10-15 mM. This, in turn, may lead to depolarization and impairment of contractile performance. The significance of elevated interfiber K+ was assessed by exposing rat muscles of uniform size (25 mg) to buffer containing 12.5-15 mM K+ and studying the decline in contractile performance and its recovery following restoration of the K+ concentration of the standard buffer (5.9 mM). When active Na(+)-K+ transport was partially inhibited by ouabain (10(-6)-10(-5) M leading to relative occupancies of 28 and 84%, respectively), the decrease in force development induced by high K+ in soleus was considerably accelerated and recovery was delayed. Conversely, when active Na(+)-K+ transport was stimulated by epinephrine, the beta 2-agonist salbutamol, or insulin, the exposure to high K+ gave a much slower decline in force. The time until full inhibition was closely correlated to the rate of Na(+)-K+ pump-mediated 86Rb uptake (r = 0.98; P less than 0.005). Significant retardation of K(+)-induced force decline could be detected down to 10(-8) M epinephrine or salbutamol. After restoration of 5.9 mM K+, recovery was promoted by epinephrine and salbutamol but not by insulin. In extensor digitorum longus muscle, insulin reduced the rate of force decline induced by exposure to 15 mM K+. The results indicate that the Na(+)-K+ pump plays a major role in the maintenance of contractility during the physiological acute exposure to high extracellular K+ associated with muscle work.

Energetics of Ca2+ homeostasis during ischemia–reperfusion on neonatal rat hearts under high-[K+] cardioplegia

2008 ◽  
Vol 86 (12) ◽  
pp. 866-879 ◽  
Author(s):  
Alicia E. Consolini ◽  
Patricia Bonazzola
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ischemia Reperfusion ◽  
Fibre Length ◽  
Neonatal Rat ◽  
Main Role ◽  
Adult Rats ◽  
Rat Hearts ◽  
High K ◽  
Contractile Recovery

The mechanocalorimetric consequences and mechanisms involved in Ca2+ homeostasis during ischemia–reperfusion (I/R) as well as the protective role of cardioplegic pretreatment with high [K+] (25 mmol/L) and low or near-normal [Ca2+] (0.5 or 2 mmol/L) were evaluated in a model of neonatal rat heart. Beating hearts from 10–12-day-old rats were perfused with Krebs solution (2 mmol/L Ca2+) under both isotonic and isometric conditions. During pretreatment, hearts were exposed for 20 min to either Krebs (control) or cardioplegia (CPG) before 15 min ischemia and 45 min reperfusion while being continuously measured for either contractility or total heat rate (Ht) in a flow calorimeter. Contractile recovery after reperfusion in hearts exposed to ischemia only (control) was higher in the isometric hearts under optimal length (87.9% ± 8.1%) than in the isotonic hearts (57.3% ± 10.6%). This same behavior was found in hearts pretreated with CPG-0.5 mmol/L Ca2+. Ht in controls was reduced from 11.5 ± 0.8 mW/g in the initial beating condition to 1.11 ± 0.33 mW/g during ischemia and was increased to 13.02 ± 0.93 mW/g (113.8% ± 5.0% of preischemic) after reperfusion. Hearts pretreated with CPG-0.5 mmol/L Ca2+ showed the same behavior. However, when extracellular calcium ([Ca]o) was increased to 2 mmol/L under CPG, isotonic hearts, but not isometric hearts, significantly increased the contractile recovery to a maximum of 88.7% ± 10.8% of preischemic levels. Ht was recovered to 92.1% ± 4.3% of preischemic, suggesting that contractile recovery was less energetically expensive after CPG-2 mmol/L Ca2+ than it was in postischemic hearts exposed to control or CPG-0.5 mmol/L Ca2+. The role of the sarcoplasmic reticulum store was evaluated by pretreating hearts with 10 mmol/L caffeine, which reduced contractile recovery only under isometric conditions or after increasing [Ca]o in CPG under isotonic conditions, suggesting that the contribution of the sarcoplasmic reticulum was dependent on the fibre length or the [Ca]o. The inhibition of the reverse mode of the sarcolemmal Na/Ca exchanger (NCX) and the mitochondrial Ca uniporter (CaU) by KB-R7943 (KBR) at 5 µmol/L in CPG-0.5 mmol/L Ca2+ improved contractile recovery of isotonic hearts, whereas it decreased Ht at the start of reperfusion, suggesting that mitochondria could uptake Ca2+ vía the mitochondrial CaU. Neither the positive inotropism nor Ht were changed by inhibiting the mitochondrial NCX with 10 µmol/L clonazepam in CPG-0.5 mmol/L Ca2+ + 5 µmol/L KBR, which suggests that the mitochondrial NCX does not have a role. Finally, the role of the forward mode of the sarcolemmal NCX was evidenced by the fall in contractile recovery with increased Ht when KBR was increased to 20 µmol/L and added to CPG-2 mmol/L Ca2+ + 10 mmol/L caffeine before I/R. Thus the sarcolemmal NCX was essential for removing the diastolic Ca2+ during the periods of CPG and I/R. In summary, Ca2+ homeostasis during I/R of neonatal rat hearts is different from that of adult rats. High-[K+] CPG protected neonatal hearts only under isotonic conditions, at a near-normal [Ca]o, or by exposure to KBR. Mitochondria were able to uptake Ca2+ via the mitochondrial CaU and reduce the Ca2+ available for contractile recovery. Nevertheless, after increasing [Ca]o in CPG, the sarcoplasmic reticulum had a main role in restoring contractility during reperfusion, as it does in adults. Thus, the degree of maturation of the heart must be taken into account to evaluate the effects of CPG and drugs on I/R.

The relationship between locus of control and hope in adolescents: The mediating role of career and talent development self-efficacy

2021 ◽  
Vol 30 (2) ◽  
pp. 129-138
Author(s):  
Mehmet Emin Turan
Keyword(s):  
Locus Of Control ◽  
Career Development ◽  
Mental Health Professionals ◽  
Self Efficacy ◽  
Structural Equation ◽  
Talent Development ◽  
Mediating Role ◽  
The Mean ◽  
The Relationship

Adolescence is a period that plays a crucial role in career development. Understanding the psychological structures associated with a career can help to better understand adolescents’ career development. The aim of this study was to examine the mediating role of career and talent development self-efficacy in the relationship between adolescents’ locus of control and the construct of children’s hope. The study group was composed of 354 adolescents including 170 females and 184 males. The mean age of participants was 14.3 years. Structural equation modelling was used to investigate the mediating role of career and talent development self-efficacy in the relationship between locus of control and children's hope. It was concluded that career and talent development self-efficacy had a mediating role in the relationship between locus of control and children’s hope. Mental health professionals and educators who carry out locus of control or hope-based interventions are recommended to pay attention to the mediating role of self-efficacy.

Influence of Na+ gradient on Ca2+ transients and contraction in vascular smooth muscle

1990 ◽  
Vol 259 (2) ◽  
pp. H409-H423 ◽  
Author(s):  
S. Bova ◽  
W. F. Goldman ◽  
X. J. Yauan ◽  
M. P. Blaustein
Keyword(s):  
Cell Activation ◽  
Rat Aorta ◽  
Resting Cells ◽  
Contractile Apparatus ◽  
A7r5 Cells ◽  
High K ◽  
K Concentration ◽  
Evoked Contractions ◽  
Artery Branch ◽  
Peripheral Cytoplasm

The effects of reducing external Na+ ([Na+]o) and increasing internal Na+ ([Na+]i) on evoked tension in arterial rings were correlated with intracellular Ca2+ transients evoked in cultured A7r5 cells. Contractions were elicited in rings of rat aorta and a small mesenteric artery branch by serotonin (5-HT), arginine vasopressin (AVP), or a high K+ concentration ([K+]o). Contractions were augmented by reduction of [Na+]o (replaced by Li+ or N-methylglucamine) or inhibition of the Na+ pump (to raise [Na+]i). These effects were dependent on external Ca2+. Ca2+ transients were measured by digital imaging of fura-2/AM-loaded A7r5 cells. The apparent free Ca2+ concentration [( Ca2+]app) in eight unstimulated cells was 110 +/- 10 nM in the peripheral cytoplasm. Activation of A7r5 cells by 5-HT, AVP, or high [K+]o evoked transient increases in [Ca2+]app. Lowering [Na+]o or raising [Na+]i elevated [Ca2+]app significantly in unstimulated cells and increased the amplitude and duration of the Ca2+ transients. These effects required external Ca2+. Caffeine (5-10 mM) reduced [Ca2+]app in resting cells and attenuated the vasoconstrictor-evoked Ca2+ transients in low [Na+]o. The data imply that Na+ gradient reduction promotes Ca2+ entry and slows Ca2+ extrusion via Na(+)-Ca2+ exchange. This increases cytosolic free Ca2+ and the intracellular Ca2+ stores so that more Ca2+ is delivered to the contractile apparatus during cell activation. Such augmented Ca2+ transients could induce the amplified vasoconstrictor-evoked contractions observed in arterial rings under reduced Na+ gradient conditions.

scholarly journals The Influence of Hotel Attributes on Brand Attachment and Post-Consumption Outcomes: The Mediating Effects of Brand Credibility

2021 ◽  
Vol 21 (1) ◽  
pp. 313-333
Author(s):  
Nadzirah Rosli ◽  
Norbani Che-Ha ◽  
Ezlika Mohd Ghazali
Keyword(s):  
Structural Equation ◽  
Future Research ◽  
Mediating Effects ◽  
Brand Attachment ◽  
Mediating Role ◽  
Brand Credibility ◽  
The Mean ◽  
Relationship Of ◽  
The Relationship

This research examine the mediating role of brand credibility between the relationship of hotel attributes and brand attachment that will to lead to post-consumption outcomes. We also examine how hotel attributes contributes to the brand attachment and post-consumption outcomes.Based on the mean-end chain theory, it explores the relationship among six constructs; hotel attributes, brand credibility, brand attachment and post-consumption outcomes (i.e., satisfaction, revisit intention and word-of-mouth). Partial Least Squares Structural Equation Modelling (PLS-SEM) approach was deployed to validate the research model. The result indicatesbrand credibility fully mediates the relationship between hotel attributes and brand attachment. Subsequently, brand credibility and brand attachment are found to be significantly linked with post-consumption outcomes. The result offers implications for hotelier and direction for future research.

K+-stimulated sugar uptake in skeletal muscle: role of cytoplasmic Ca2+

1983 ◽  
Vol 245 (1) ◽  
pp. C125-C132 ◽  
Author(s):  
P. Valant ◽  
D. Erlij
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Cytochalasin B ◽  
Sugar Transport ◽  
Sugar Uptake ◽  
Frog Skeletal Muscle ◽  
High K ◽  
K Concentration ◽  
External K

We have compared the effects of insulin with those of elevated external K+ concentration ([K+]o) on sugar uptake and protein synthesis by frog skeletal muscle. When [K+]o was between 0.5 and 15 mM there were no effects on uptake; however, when 20 mM was used a significant increase was observed. Further increases in [K+]o caused larger stimulations of uptake. The stimulation persisted for 2.5 h after washing the high [K+]o. The stimulations caused by both insulin and high K+ were markedly inhibited by cytochalasin B. Dantrolene nearly abolished the response to high K+, whereas it had only minor effects on the resting sugar uptake and on the stimulations caused by either insulin or epinephrine. These results suggest that while both insulin and high K+ activate the cytochalasin-sensitive transport system of sugar transport, each agent must act through a different pathway, because only the effects of high K+ were dantrolene sensitive. The effect of dantrolene suggests that the enhancement of sugar transport caused by high K+ is due to an increase of cytoplasmic Ca2+. In contrast to insulin, high K+ did not modify the rate of protein synthesis.

Hair cell changes after cationic stimulation of corti's organ

1989 ◽  
Vol 47 ◽  
pp. 798-799
Author(s):  
Cesar D. Fermin ◽  
Hans-Peter Zenner
Keyword(s):  
Organ Of Corti ◽  
Cross Sectional ◽  
Surface Areas ◽  
High K ◽  
Anatomical Arrangement ◽  
Cell Cytosol ◽  
High Concentrations ◽  
K Concentration ◽  
Cell Changes

Contraction of outer and inner hair cells (OHC&IHC) in the Organ of Corti (OC) of the inner ear is necessary for sound transduction. Getting at HC in vivo preparations is difficult. Thus, isolated HCs have been used to study OHC properties. Even though viability has been shown in isolated (iOHC) preparations by good responses to current and cationic stimulation, the contribution of adjoining cells can not be explained with iOHC preparations. This study was undertaken to examine changes in the OHC after expossure of the OHC to high concentrations of potassium (K) and sodium (Na), by carefully immersing the OC in either artifical endolymph or perilymph. After K and Na exposure, OCs were fixed with 3% glutaraldehyde, post-fixed in osmium, separated into base, middle and apex and embedded in Araldite™. One μm thick sections were prepared for analysis with the light and E.M. Cross sectional areas were measured with Bioquant™ software.Potassium and sodium both cause isolated guinea pig OHC to contract. In vivo high K concentration may cause uncontrolled and sustained contractions that could contribute to Meniere's disease. The behavior of OHC in the vivo setting might be very different from that of iOHC. We show here changes of the cell cytosol and cisterns caused by K and Na to OHC in situs. The table below shows results from cross sectional area measurements of OHC from OC that were exposed to either K or Na. As one would expect, from the anatomical arrangement of the OC, OHC#l that are supported by rigid tissue would probably be displaced (move) less than those OHC located away from the pillar. Surprisingly, cells in the middle turn of the cochlea changed their surface areas more than those at either end of the cochlea. Moreover, changes in surface area do not seem to differ between K and Na treated OCs.

The More You Say, the Less They Hear

2015 ◽  
Vol 27 (4) ◽  
pp. 159-169 ◽  
Author(s):  
Elsbeth D. Asbeek Brusse ◽  
Marieke L. Fransen ◽  
Edith G. Smit
Keyword(s):  
Hearing Protection ◽  
Entertainment Education ◽  
Mediating Role ◽  
Attitude Measures ◽  
Underlying Mechanisms

Abstract. This study examined the effects of disclosure messages in entertainment-education (E-E) on attitudes toward hearing protection and attitude toward the source. In addition, the (mediating) role of the underlying mechanisms (i.e., transportation, identification, and counterarguing) was studied. In an experiment (N = 336), three different disclosure messages were compared with a no-disclosure condition. The results show that more explicit disclosure messages negatively affect transportation and identification and stimulate the generation of counterarguments. In addition, the more explicit disclosure messages affect both attitude measures via two of these processes (i.e., transportation and counterarguing). Less explicit disclosure messages do not have this effect. Implications of the findings are discussed.

Coping Humor as a Mediator Between Emotional Intelligence and Job Satisfaction

2017 ◽  
Vol 16 (3) ◽  
pp. 155-159 ◽  
Author(s):  
Peizhen Sun ◽  
Jennifer J. Chen ◽  
Hongyan Jiang
Keyword(s):  
Job Satisfaction ◽  
Emotional Intelligence ◽  
Future Research ◽  
Satisfaction Scale ◽  
Primary School Teachers ◽  
Mediating Role ◽  
Regulation Of Emotion ◽  
The Relationship ◽  
Overall Job Satisfaction

Abstract. This study investigated the mediating role of coping humor in the relationship between emotional intelligence (EI) and job satisfaction. Participants were 398 primary school teachers in China, who completed the Wong Law Emotional Intelligence Scale, Coping Humor Scale, and Overall Job Satisfaction Scale. Results showed that coping humor was a significant mediator between EI and job satisfaction. A further examination revealed, however, that coping humor only mediated two sub-dimensions of EI (use of emotion and regulation of emotion) and job satisfaction. Implications for future research and limitations of the study are discussed.

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