scholarly journals The effect of hyperosmolality on the rate of heat production of quiescent trabeculae isolated from the rat heart.

1996 ◽  
Vol 108 (6) ◽  
pp. 497-514 ◽  
Author(s):  
D S Loiselle ◽  
G J Stienen ◽  
C van Hardeveld ◽  
E T van der Meulen ◽  
G I Zahalak ◽  
...  
Keyword(s):  
Heat Production ◽  
Calcium Concentration ◽  
Thermal Response ◽  
Force Production ◽  
Active Force ◽  
Release Channel ◽  
The Face ◽  
Increased Activity ◽  
External Calcium ◽  
Ventricular Trabeculae

We have measured the rate of heat production of isolated, quiescent, right ventricular trabeculae of the rat under isosmotic and hyperosmotic conditions, using a microcalorimetric technique. In parallel experiments, we measured force production and intracellular calcium concentration ([Ca2+]i). The rate of resting heat production under isosmotic conditions (mean +/- SEM, n = 32) was 100 +/- 7 mW (g dry wt)-1; it increased sigmoidally with osmolality, reaching a peak that was about four times the isosmotic value at about twice normal osmotic pressure. The hyperosmotic thermal response was: (a) abolished by anoxia, (b) attenuated by procaine, (c) insensitive to verapamil, ouabain, and external calcium concentration, and (d) absent in chemically skinned trabeculae bathed in low-Ca2+ "relaxing solution." Active force production was inhibited at all osmolalities above isosmotic. Passive (tonic) force increased to, at most, 15% of the peak active force developed under isosmotic conditions while [Ca2+]i increased, at most, 30% above its isosmotic value. We infer that hyperosmotic stimulation of resting cardiac heat production reflects, in large part, greatly increased activity of the sarcoplasmic reticular Ca2+ ATPase in the face of increased efflux via a procaine-inhibitable Ca(2+)-release channel.

The origin of passive force enhancement in skeletal muscle

2008 ◽  
Vol 294 (1) ◽  
pp. C74-C78 ◽  
Author(s):  
V. Joumaa ◽  
D. E. Rassier ◽  
T. R. Leonard ◽  
W. Herzog
Keyword(s):  
Calcium Concentration ◽  
Force Production ◽  
Primary Source ◽  
Passive Force ◽  
Active Force ◽  
Force Enhancement ◽  
Bridge Formation ◽  
Calcium Dependent ◽  
Cross Bridge ◽  
High Calcium

The aim of the present study was to test whether titin is a calcium-dependent spring and whether it is the source of the passive force enhancement observed in muscle and single fiber preparations. We measured passive force enhancement in troponin C (TnC)-depleted myofibrils in which active force production was completely eliminated. The TnC-depleted construct allowed for the investigation of the effect of calcium concentration on passive force, without the confounding effects of actin-myosin cross-bridge formation and active force production. Passive forces in TnC-depleted myofibrils ( n = 6) were 35.0 ± 2.9 nN/ μm2 when stretched to an average sarcomere length of 3.4 μm in a solution with low calcium concentration (pCa 8.0). Passive forces in the same myofibrils increased by 25% to 30% when stretches were performed in a solution with high calcium concentration (pCa 3.5). Since it is well accepted that titin is the primary source for passive force in rabbit psoas myofibrils and since the increase in passive force in TnC-depleted myofibrils was abolished after trypsin treatment, our results suggest that increasing calcium concentration is associated with increased titin stiffness. However, this calcium-induced titin stiffness accounted for only ∼25% of the passive force enhancement observed in intact myofibrils. Therefore, ∼75% of the normally occurring passive force enhancement remains unexplained. The findings of the present study suggest that passive force enhancement is partly caused by a calcium-induced increase in titin stiffness but also requires cross-bridge formation and/or active force production for full manifestation.

scholarly journals Expressed Na channel clones differ in their sensitivity to external calcium concentration

1992 ◽  
Vol 62 (1) ◽  
pp. 37-40 ◽  
Author(s):  
M. Chahine ◽  
L.Q. Chen ◽  
R.G. Kallen ◽  
R.L. Barchi ◽  
R. Horn
Keyword(s):  
Calcium Concentration ◽  
Na Channel ◽  
External Calcium

scholarly journals Stretch and quick release of rat cardiac trabeculae accelerates Ca2+ waves and triggered propagated contractions

2001 ◽  
Vol 281 (5) ◽  
pp. H2133-H2142 ◽  
Author(s):  
Yuji Wakayama ◽  
Masahito Miura ◽  
Yoshinao Sugai ◽  
Yutaka Kagaya ◽  
Jun Watanabe ◽  
...  
Keyword(s):  
Strain Gauge ◽  
Sarcomere Length ◽  
Muscle Length ◽  
Laser Diffraction ◽  
Active Force ◽  
Quick Release ◽  
Rat Hearts ◽  
Initiation And Propagation ◽  
Intracellular Ca ◽  
Ventricular Trabeculae

Rapid shortening of active cardiac muscle [quick release (QR)] dissociates Ca2+ from myofilaments. We studied, using muscle stretches and QR, whether Ca2+ dissociation affects triggered propagated contractions (TPCs) and Ca2+waves. The intracellular Ca2+ concentration was measured by a SIT camera in right ventricular trabeculae dissected from rat hearts loaded with fura 2 salt, force was measured by a silicon strain gauge, and sarcomere length was measured by laser diffraction while a servomotor controlled muscle length. TPCs ( n = 27) were induced at 28°C by stimulus trains (7.5 s at 2.65 ± 0.13 Hz) at an extracellular Ca2+ concentration ([Ca2+]o) = 2.0 mM or with 10 μM Gd3+ at [Ca2+]o = 5.2 ± 0.73 mM. QR during twitch relaxation after a 10% stretch for 100–200 ms reduced both the time between the last stimulus and the peak TPC (PeakTPC) and the time between the last stimulus and peak Ca2+ wave (PeakCW) and increased PeakTPC and PeakCW ( n= 13) as well as the propagation velocity ( V prop; n = 8). Active force during stretch also increased V prop( r = 0.84, n = 12, P < 0.01), but Gd3+ had no effect ( n = 5). These results suggest that Ca2+ dissociation by QR during relaxation accelerates the initiation and propagation of Ca2+ waves.

The resting membrane potential of Drosophila melanogaster larval muscle depends strongly on external calcium concentration

2010 ◽  
Vol 56 (3) ◽  
pp. 304-313 ◽  
Author(s):  
Jacob L. Krans ◽  
Karen D. Parfitt ◽  
Kristin D. Gawera ◽  
Patricia K. Rivlin ◽  
Ronald R. Hoy
Keyword(s):  
Drosophila Melanogaster ◽  
Membrane Potential ◽  
Calcium Concentration ◽  
Resting Membrane Potential ◽  
Larval Muscle ◽  
External Calcium

The energetic cost of activation of white muscle fibres from the dogfish Scyliorhinus canicula

1997 ◽  
Vol 200 (3) ◽  
pp. 495-501 ◽  
Author(s):  
F Lou ◽  
N Curtin ◽  
R Woledge
Keyword(s):  
Heat Production ◽  
White Muscle ◽  
Isometric Force ◽  
Force Production ◽  
Total Heat ◽  
Energetic Cost ◽  
Maximum Efficiency ◽  
Muscle Fibres ◽  
Scyliorhinus Canicula ◽  
A Value

The energetic cost of activation was measured during an isometric tetanus of white muscle fibres from the dogfish Scyliorhinus canicula. The total heat production by the fibres was taken as a measure of the total energetic cost. This energy consists of two parts. One is due to crossbridge interaction which produces isometric force, and this part varies linearly with the degree of filament overlap in the fibres. The other part of the energy is that associated with activation of the crossbridges by Ca2+, mainly with uptake of Ca2+ into the sarcoplasmic reticulum by the ATP-driven Ca2+ pump. Total heat production was measured at various degrees of filament overlap beyond the optimum for force development. Extrapolation of heat versus force production data to evaluate the heat remaining at zero force gave a value of 34&plusmn;5 % (mean &plusmn; s.e.m., N=24) for activation heat as a percentage of total heat production in a 2.0 s isometric tetanus. Values for 0.4 and 1.0 s of stimulation were similar. Comparison with values in the literature shows that the energetic cost of activation in dogfish muscle is very similar to that of frog skeletal muscle and it cannot explain the lower maximum efficiency of dogfish muscle compared with frog muscle. The proportion of energy for activation (Ca2+ turnover) is similar to that expected from a simple model in which Ca2+ turnover was varied to minimize the total energy cost for a contraction plus relaxation cycle.

The Effect of Changed Extracellular Calcium and Sodium Concentration on the Electroretinogram of the Crayfish Retina

1980 ◽  
Vol 35 (3-4) ◽  
pp. 308-318 ◽  
Author(s):  
H. Stieve ◽  
I. Claßen-Linke
Keyword(s):  
Dark Adaptation ◽  
Time Course ◽  
Calcium Concentration ◽  
Light Adaptation ◽  
Sodium Concentration ◽  
Strong Increase ◽  
Calcium Stores ◽  
Half Time ◽  
Astacus Leptodactylus ◽  
External Calcium

Abstract The electroretinogram (ERG) of the isolated retina of the crayfish Astacus leptodactylus evoked by strong 10 ms light flashes at constant 5 min intervals was measured while the retina was continuously superfused with various salines which differed in Ca2+ -and Na+ -concentrations. The osmotic pressure of test- and reference-saline was adjusted to be identical by adding sucrose. Results: 1. Upon raising the calcium-concentration of the superfusate in the range of 20-150 mmol/l (constant Na+ -concentration: 208 mmol/l) the peak amplitude hmax and the half time of decay t2 of the ERG both decrease gradually up to about 50% in respect to the corresponding value in reference saline. 2. The recovery of the ERG due to dark adaptation following the “weakly light adapted state” is greatly diminished in high external [Ca2+]ex. 3. Lowering the external calcium-concentration (10 →1 mmol/l) causes a small increase in hmax and a strong increase of the half time of decay t2 (about 180%). Upon lowering the calcium concentration of the superfusate to about 1 nmol/l by 1 mmol/l of the calcium buffer EDTA, a slowly augmenting diminution of the ERG height hm SLX occurs. How­ever, a strong retardation of the falling phase of the ERG characterized by an increase in t2 occurs quickly. Even after 90 min stay in the low calcium saline the retina is still not inexcitable; hmax is 5 - 10% of the reference value. The diminution of hmax occurs about six-fold faster when the buffer concentration is raised to 10 mmol/l EDTA. 4. Additional lowering of the Na+ -concentration (208 →20.8 mmol/l) in a superfusate with a calcium concentration raised to 150 mmol/l causes a strong reduction of the ERG amplitude hmax to about 10%. 5. In a superfusate containing 1 nmol/l calcium such lowering of the sodium concentration (208 → 20.8 mmol/l) causes a diminution of the ERG height to about 40% and the shape of the ERG to become polyphasic; at least two maxima with different time to peak values are observed. Interpretation: 1. The similarity of effects, namely raising external calcium concentration and light adaptation on the one hand and lowering external calcium and dark adaptation on the other hand may indicate that the external calcium is acting on the adaptation mechanism of the photoreceptor cells, presumably by influencing the intracellular [Ca2+]. 2. The great tolerance of the retina against Ca2+ -deficiency in the superfusate might be effected by calcium stores in the retina which need high Ca2+ -buffer concentrations in the superfusate to become exhausted. 3. In contrast to the Limulus ventral nerve photoreceptor there does not seem to be an antagonis­ tic effect of sodium and calcium in the crayfish retina on the control of the light channels. 4. The crayfish receptor potential seems to be composed of at least two different processes. Lowering calcium-and lowering external sodium-concentration both diminish the height and change the time course of the two components to a different degree. This could be caused by in­ fluencing the state of adaptation and thereby making the two maxima separately visible.

Effects of Ca2+ and catecholamines on the guinea pig atrium action potential plateau

1977 ◽  
Vol 233 (2) ◽  
pp. H203-H210
Author(s):  
R. B. Robinson ◽  
W. W. Sleator
Keyword(s):  
Guinea Pig ◽  
Calcium Concentration ◽  
Potassium Conductance ◽  
Slow Inward Current ◽  
Activation Process ◽  
Action Potential Plateau ◽  
Guinea Pig Atrium ◽  
Opposing Effects ◽  
Guinea Pig Atria ◽  
External Calcium

The activation process in isolated electrically driven guinea pig atria was studied by means of simultaneous microelectrode and tension recording. Reducing external calcium from 2.5 to 1.25 mM prolonged the plateau but further reduction of calcium shortened it. Progressively increasing doses of the calcium antagonist D600 (up to 1.4 micrometer), however, monotonically decreased plateau duration. Either protocol monotonically decreased steady-state tension, but with markedly different effects on the restitution relation. Epinephrine, and to a lesser extent isoproterenol, restored plateau duration after exposure to either a calcium-free or D600-containing solution, but only the isoproterenol effect was propranolol sensitive. Addition of calcium chelators enhanced rather than prevented the effect of epinephrine on plateau duration in a calcium-free solution, extending the plateau duration to more than 3 times normal in some cases. These results are explained in terms of two opposing effects of a change in calcium concentration on plateau formation, one action being through the slow inward current and the second through a shift in a calcium dependence of the inward-rectifying, potassium conductance system.

Invariance of Stoichiometry of the Sarcoplasmic Reticulum Calcium Pump at Physiological Calcium Concentrations – a Reevaluation

1985 ◽  
Vol 40 (7-8) ◽  
pp. 571-575 ◽  
Author(s):  
Wilhelm Hasselbach ◽  
Andrea Migala
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Level ◽  
Calcium Concentration ◽  
Calcium Uptake ◽  
Atp Hydrolysis ◽  
Calcium Pump ◽  
Oxalate Precipitation ◽  
Sarcoplasmic Reticulum Calcium ◽  
Internal Calcium ◽  
External Calcium

Abstract The decline of the transport ratio of the sarcoplasmic calcium pump observed in a recent study (A. results from the retardation of calcium oxalate precipitation at low calcium/protein ratios. The prevailing high internal calcium level supports a rapid calcium backflux and a compensatory ATP hydrolysis during net calcium uptake which reduces the transport ratio. Yet, the determined calcium back­ flux does not fully account for the decline of the transport ratio. A supposed modulation of the stoichiometry of the pump by external calcium (0.1 μм) is at variance with results of previous studies showing a constant transport ratio of two in the same calcium concentration range.

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