| 1. |
- Arheden, Håkan, et al.
(författare)
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Calcium sensitivity and energetics of contraction in skinned smooth muscle of the guinea pig taenia coli at altered pH
- 1989
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Ingår i: Pflügers Archiv. - 0031-6768. ; 413:5, s. 476-481
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Tidskriftsartikel (refereegranskat)abstract
- Calcium-sensitivity of contraction, force-velocity relation and ATP hydrolysis rate at different pH (6.2-7.8) were investigated in skinned smooth muscle preparations from the guinea pig taenia coli. Varied free-calcium levels were buffered by 4 mM BAPTA (1,2-bis(2-aminophenoxy)-ethane-N,N,N'N'-tetraacetic acid) which has calcium binding properties little affected by pH. A small increase of calcium-sensitivity of contraction was seen at pH 6.2 compared to 6.9 and 7.8 (ED50 shift of about 0.15 pCa units). The isometric force and Vmax in fibres activated either by calcium or by thiophosphorylation of the myosin light chains were each reduced by about 15% at pH 6.2 compared to 6.9 and 7.8. Following an isotonic quick release the shortening velocity decreases with time. This effect was more pronounced at pH 6.2 than at pH 6.9 or 7.8. The ATP hydrolysis rates in relaxed and thiophosphorylated fibres were essentially unaffected by alteration in pH between 6.2 and 7.8. Due to the lower force, energetic cost of force maintenance was thus somewhat increased at pH 6.2. These results suggest that pH alteration between 6.2 and 7.8 have effects on the properties of the contractile machinery of the smooth muscle in the skinned guinea pig taenia coli. The effects are however small and therefore probably of little functional importance over a pH range which should cover most cases of intracellular pH alteration under physiological or pathophysiological conditions.
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| 2. |
- Arheden, Håkan, et al.
(författare)
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Cross-bridge behaviour in skinned smooth muscle of the guinea-pig taenia coli at altered ionic strength
- 1988
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Ingår i: Journal of Physiology. - 1469-7793. ; 403, s. 539-558
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Tidskriftsartikel (refereegranskat)abstract
- 1. The effects of varied levels (25-300 mM) of ionic strength on mechanical properties and ATP hydrolysis rate of chemically skinned guinea-pig taenia coli fibres were investigated. 2. The tension development following activation by calcium (pCa 4 8), and relaxation following removal of calcium (pCa 9), were slower in 25 mm compared to 150 mm ionic strength. In fibres activated by thiophosphorylation of myosin light chains, by exposure to ATP-y-S, the tension development was rapid and independent of ionic strength. 3. The maximal shortening velocity (Vmax) was obtained from force-velocity relations determined by the quick-release method. The rate of ATP hydrolysis (JATP) was determined by measurement of pyruvate released from phosphoenolpyruvate (PEP). In order to obtain maximal Vmax and JATP at a Mg-ATP concentration of 1 mm, an ATP regenerating system was required. In thiophosphorylated fibres 2 mmphosphocreatine (PCr) or 3-2 mM-PEP were adequate for maximal Vmax and JATP respectively. In calcium-activated fibres 5 mM-PCr was required for maximal Vmax. 4. The isometric force of thiophosphorylated fibres showed a biphasic dependence on ionic strength with a maximum at 90 mm. Vmax was essentially unchanged between 50 and 200 mm ionic strength. At 25 mm ionic strength, isometric force and Vmax were decreased by, respectively, about 15 and 25%. At 250 mM ionic strength, isometric force and Vmax were decreased by, respectively, 47 and 33 %. 5. Vm.x decreased with decreasing [Mg-ATP]. At [Mg-ATP] less than 0 1 mm there was no difference in Vmax between 35 and 150 mM ionic strength. At 250 mM ionic strength Vmax was lower than that at 150 mm at all [Mg-ATP]. 6. JATP during contraction in thiophosphorylated fibres at 35, 150 and 250 mm ionic strength was respectively, 0-62, 0-98 and 0-93 ,umol g-1 min-'. The energetic tension cost (JATP/force) increased with ionic strength. 7. The force response to a quick stretch was investigated in the relaxed, contracted and rigor states at 25, 150 and 250 mm ionic strength. Stiffness in the relaxed state increased with speed of stretch and was higher the lower the ionic strength. In the contracted and rigor states, stiffness was also affected by ionic strength, but the relative effect in the contracted state was small. 8. The effects of ionic strength on the behaviour of the skinned smooth muscle fibre may involve an influence on the filament system, but are also compatible with an increased binding of smooth muscle myosin to actin at low ionic strength. The results from activated and rigor muscle suggest that ionic strength does not exclusively affect kinetics of rapid cross-bridge equilibria but may also influence mechanical properties of attached cross-bridge states.
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| 3. |
- Arheden, Håkan, et al.
(författare)
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Dissociation between force and [Ca2+]i during extra systoles in guinea-pig ventricular muscle microinjected with fura-2
- 1999
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Ingår i: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772. ; 165:1, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- Thin trabeculae were dissected from the right ventricle of guinea-pig heart and stimulated to contract isometrically at 0.5 Hz (26 degrees C). Rapid and transient changes of force were obtained by inducing three extra systoles (ES1-3) at 450-ms intervals. The two regular contractions (P1-2) following (ES1-3) were potentiated. Fura-2 salt was microinjected into the preparation to monitor intracellular calcium ([Ca2+]i). Three distinct phases of [Ca2+]i were seen: (1) a rapid rising phase to about 200 nmol L(-1), (2) a slower rising phase to a peak at 400 nmol L(-1), and (3) a slow decline to about 50 nmol L(-1). During ES1, there was a discrepancy between force, which decreased, and peak [Ca2+]i, which increased to 600 nmol L(-1). It is likely that the increased [Ca2+]i during the extra systoles reflects increased sarcolemmal calcium inflow, causing post-extra-systolic potentiation. Ryanodine (1-2 microM) was added to inhibit the intracellular calcium release and thus reduce the intracellular [Ca2+]i gradients following excitation. Ryanodine inhibited phase 1 of [Ca2+]i and abolished post-extra-systolic potentiation. There was a close relationship between dF/dt and [Ca2+]i with ryanodine during control and ES1-3. It is likely that fura-2 reports a spatially averaged [Ca2+]i and that phase 1 of the signal therefore apparently underestimates activator calcium in the close vicinity of the contractile elements.
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| 4. |
- Arheden, Håkan, et al.
(författare)
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Force response to rapid length change during contraction and rigor in skinned smooth muscle of guinea-pig taenia coli
- 1991
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Ingår i: Journal of Physiology. - 1469-7793. ; 442, s. 601-630
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Tidskriftsartikel (refereegranskat)abstract
- 1. Mechanical transients in fibre bundles of skinned smooth muscle of guinea-pig taenia coli at 21-22 degrees C were investigated by recording tension responses to length changes of up to 9%, complete within 0.3 ms. 2. The length-force relationship, recorded continuously during rapid stretch of a Ca(2+)-activated contracted muscle, was linear up to at least 2.5 times the isometric force, corresponding to a stretch of about 1%. The slope of the relationship (stiffness) increased with the velocity of stretch. 3. During rapid release (about 120 muscle lengths s-1) the length-force relationship was linear down to about 50% of the initial isometric force, reached at about 80 microseconds after the beginning of the release. At lower force the length-force relationship was concave upwards. The linear portion extrapolated to zero force at about -0.008 muscle lengths. In large releases the length-force plot approached the force baseline under an acute angle, and negative force was transiently exerted. 4. When the muscle was stretched back to the initial length after a shortening step, force transiently rose above the isometric force, but decayed back within a few milliseconds. Stiffness at the time of restretch was compared with that in the initial shortening step by plotting force vs. length, and was found to be decreased to 63% within 0.3 ms of a step to zero force. Stiffness decreased further with time at zero force, and after 256 ms was about 29% of the isometric value. 5. In rigor, caused by the introduction of ATP-free solution during the plateau of isometric contraction, fibre tension decreased to about 30% of the active tension, whereas stiffness relative to force increased; 82% of the initial stiffness in rigor was detected in a restretch immediately after a shortening step, decreasing to 59% at 256 ms. When the fibre was activated at suboptimal [Ca2+] to cause the same force as in rigor, stiffness was lower than in rigor and decreased more after a release. 6. After completion of a release-stretch cycle, stiffness was rapidly restored to the same value as in isometric contraction. Test stretches at different points in time after completion of the cycle revealed that most of the stiffness had been restored within 1 ms of the restretch, occurring concomitantly with a decay in force.7. The shape of the length-force relationship during a release was analysed using a model consisting of a linear (cross-bridge) elasticity in series with an exponential (passive) elasticity and assuming no detachment of cross-bridges during release. In rigor the exponential element contributed 40% of the total compliance of the fibre. The model, although closely fitting the data, could not account for the results using an exponential elasticity with unaltered properties during activation at optimal and suboptimal [Ca2"] and in rigor. 8. The results suggest rapid detachment of some of the attached cross-bridges during and after a shortening step to slack length. Detachment of strongly bound cross-bridges may occur during a restretch, if it causes a strain on the attached crossbridges exceeding their working range. During the restretch, and on return to isometric contraction after the restretch, cross-bridges rapidly reattach in strongly bound configurations.
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| 5. |
- Arheden, Håkan, et al.
(författare)
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Force-velocity relation and rate of ATP hydrolysis in osmotically compressed skinned smooth muscle of the guinea pig
- 1987
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Ingår i: Journal of Muscle Research and Cell Motility. - 0142-4319. ; 8:2, s. 151-160
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Tidskriftsartikel (refereegranskat)abstract
- Chemically skinned guinea pig taenia coli fibre bundles showed a concentration-dependent decrease in width when incubated in media containing Dextran T500 (0-0.2 g ml-1). The maximal reduction in width, observed at 0.2 g ml-1 dextran, was 32%. The effect was reversible upon removal of dextran. Isometric force was slightly increased (about 10%) at the lowest dextran concentration (0.025 g ml-1) but decreased at higher concentrations (40% decrease at 0.2 g/ml-1). The energetic tension cost (ATP turnover/force) was decreased by about 40% after dextran addition. Force development and relaxation were markedly slower in 0.1 g ml-1 and absent in 0.2 g ml-1 dextran. In isotonic quick-release experiments 0.025 g ml-1 dextran did not influence maximal shortening velocity (Vmax) and relative stiffness, whereas 0.1 g ml-1 markedly increased stiffness and decreased Vmax to about 27%. Vanadate induced relaxation in the activated muscle (pCa 4.5) both in the absence and presence (0.1 g ml-1) of dextran and increased the rate of relaxation (pCa 9) at 0.1 g ml-1 dextran. The isometric rate of crossbridge turnover, as reflected by the energetic tension cost and the rate of relaxation, was decreased at all degrees of osmotic compression. Crossbridge turnover rate during shortening (Vmax) was unaffected at an osmotic compression of 12% (width) but was decreased at higher compression (32%).
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| 6. |
- Hellstrand, Per, et al.
(författare)
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Mechanical transients in smooth muscle
- 1989
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Ingår i: Progress in Clinical and Biological Research. - 0361-7742. ; 315, s. 347-357
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Tidskriftsartikel (refereegranskat)
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| 7. |
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