| 11. |
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| 12. |
- Arner, Anders, et al.
(författare)
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Cross-bridge cycling in smooth muscle: a short review
- 1998
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772. ; 164:4, s. 363-372
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Tidskriftsartikel (refereegranskat)abstract
- This review is focused on the cross-bridge interaction of the organized contractile system of smooth muscle fibres. By using chemically skinned preparations the different enzymatic reactions of actin-myosin interaction have been associated with mechanical events. A rigor state has been identified in smooth muscle and the binding of ATP causes dissociation of rigor cross-bridges at rates slightly slower than those in skeletal muscle, but fast enough not to be rate-limiting for cross-bridge turn over in the muscle fibre. The release of inorganic phosphate (Pi) is associated with force generation, and this process is not rate-limiting for maximal shortening velocity (Vmax) in the fully activated muscle. The binding of ADP to myosin is strong in the smooth muscle contractile system, a property that might be associated with the generally slow cross-bridge turn over. Both force and Vmax are modulated by the extent of myosin light chain phosphorylation. Low levels of activation are considered to be associated with the recruitment of slowly cycling dephosphorylated cross-bridges which reduces shortening velocity. The attachment of these cross-bridge states in skinned smooth muscles can be regulated by cooperative mechanisms and thin filament associated systems. Smooth muscles exhibit a large diversity in their Vmax and the individual smooth muscle tissue can alter its Vmax under physiological conditions. The diversity and the long-term modulation of phenotype are associated with changes in myosin heavy and light chain isoform expression.
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| 13. |
- Arner, Anders, et al.
(författare)
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Effects of Ca2+ on force-velocity characteristics of normal and hypertrophic smooth muscle of the rat portal vein
- 1985
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772. ; 124:4, s. 525-533
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Tidskriftsartikel (refereegranskat)abstract
- Portal hypertension was induced in rats by partial ligation of the hepatic branches of the portal vein. After 5 days of hypertension the portal veins were taken out and mounted for isometric and quick-release experiments. Portal veins from sham-operated normal rats served as controls. The ligated veins had an increased cross-sectional area, indicating smooth-muscle hypertrophy. Although the absolute magnitude of active force of these veins was increased, the active force per cross-sectional area was decreased, indicating an alteration in the properties of the contractile system. No difference in the Ca2+ concentration-response relations to K+-activated intact control and hypertrophic veins was found. In chemically skinned preparations, devoid of functional plasma membranes, the hypertrophic veins had similar Ca2+ sensitivity (in the presence of I microM calmodulin) but a lower force per cross-sectional area. Force-velocity relations were determined in K+-activated intact preparations. In control veins a reduction in extracellular Ca2+ was associated with a significant reduction in both isometric force and maximal shortening velocity (Vmax). In hypertrophic veins the decreased isometric force at maximal activation was associated with a low Vmax. A comparison between hypertrophic and submaximally stimulated control vessels showed corresponding Vmax and isometric force values. We conclude that the low isometric force of hypertrophic veins is associated with a lower rate of cross-bridge turnover. This could be an effect of alterations in the activation mechanisms or in the intrinsic properties of the contractile system itself.
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| 14. |
- Arner, Anders, et al.
(författare)
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Effects of calcium and substrate on force-velocity relation and energy turnover in skinned smooth muscle of the guinea-pig
- 1985
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Ingår i: Journal of Physiology. - 1469-7793. ; 360, s. 347-365
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Tidskriftsartikel (refereegranskat)abstract
- Mechanical properties and rate of ATP breakdown (JATP) have been determined in the chemically skinned guinea-pig taenia coli at 22 degrees C. The influence of varied [Ca2+], [Mg ATP] and muscle length were investigated. The shortening response after a step decrease in force (isotonic quick release) was highly curvilinear in the first 100-200 ms. This effect was shown to be a time-dependent response to the force step and not primarily caused by the shift along the length-force relation associated with shortening. Maximal shortening velocity (Vmax) decreased gradually following the release. At pCa (= -log [Ca2+]) 4.5, Vmax at 20 and 1000 ms after release was 0.49 +/- 0.07 and 0.041 +/- 0.004 (mean +/- S.E. of mean, n = 5) lengths s-1 respectively. Unloaded shortening velocity obtained from length steps of different magnitude (slack test) also showed a gradual decrease after the release, consistent with the isotonic release results. Increasing [Ca2+] from the relaxed state at pCa 9 (1 microM-calmodulin present) gave increased isometric force to a maximum at pCa 4.5. Half-maximal response was obtained at pCa 6.1. JATP at maximal force at pCa 4.5 was about 3 times the basal rate at pCa 9. The relation between JATP and force was highly non-linear, with a marked increase in JATP with little alteration in force at the highest [Ca2+]. When force was reduced to zero at pCa 4.5 by shortening the muscle to 0.3 L0 (L0 being the length giving maximal active force), JATP decreased by about 30%. At two levels of [Ca2+] giving similar force (pCa 5.75 and 4.5) the energetic tension cost obtained by length variations was lower at the low [Ca2+]. At pCa 6.0, Vmax and force were decreased to the same extent relative to their values at pCa 4.5. At pCa 5.75, where there was no reduction in force but a 25% decrease in isometric JATP, Vmax was unchanged relative to pCa 4.5. Force, Vmax and JATP were all dependent on [Mg ATP]. Half-maximal response was obtained at 0.1 mM for force and Vmax, and at 0.5 mM for JATP. The results are discussed in relation to a possible influence of both Ca2+ and Mg ATP on kinetic properties of the cross-bridge cycle.
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| 15. |
- Arner, Anders, et al.
(författare)
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Energy turnover and lactate dehydrogenase activity in detrusor smooth muscle from rats with streptozotocin-induced diabetes
- 1993
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772. ; 147:4, s. 375-383
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Tidskriftsartikel (refereegranskat)abstract
- Force generation and tissue glucose metabolism were measured in the urinary bladder smooth muscle from rats with streptozotocin-induced diabetes (7-8 wk duration). Bladder wet wt was almost 4-fold higher in the diabetic animals compared with the untreated controls. Morphological analysis showed that the growth was associated with hypertrophy of the smooth muscle component in the bladder wall. Force generation of isolated bladder strip preparations was measured in vitro at different ambient oxygen tensions. Activation of intramural nerves, with electrical field stimulation, induced contractions that were unaffected by reduction of oxygen tension down to PO2 100 mmHg for both control and diabetic muscle strips. At zero PO2 force was reduced by approximately 10-20%, in both groups. High-K+ solution induced 'tonic' contractions that were slightly more inhibited by lowering PO2. At intermediate PO2 (between 100 and 20 mmHg) the diabetic muscle gave slightly higher force. At zero PO2 no significant difference could be detected between strips from control and diabetic animals. Oxygen consumption and lactate production in the preparations were determined at a PO2 of 290 mmHg and related to the volume of smooth muscle. At zero PO2, lactate formation increased 3- to 4-fold. The metabolic tension cost was lower at zero PO2. No differences in basal and contraction related metabolic rates could be detected between the two groups under normoxic and anoxic conditions. The maximal activity of lactate dehydrogenase (LDH) determined in tissue samples was about 2-fold higher in the diabetic bladder muscle.(ABSTRACT TRUNCATED AT 250 WORDS)
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| 16. |
- Arner, Anders, et al.
(författare)
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Energy turnover and mechanical properties of resting and contracting aortas and portal veins from normotensive and spontaneously hypertensive rats
- 1981
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Ingår i: Circulation Research. - 0009-7330. ; 48:4, s. 539-548
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Tidskriftsartikel (refereegranskat)abstract
- Aortas and portal veins from spontaneously hypertensive rats (SHR) and matched normotensive Wistar-Kyoto rats (WKY) were studied with respect to their energy turnover and mechanical properties. Relaxed aortas fom SHR 16--17 weeks and 20--25 weeks of age were stiffer, had smaller circumference, and greater maximal active wall tension compared to WKY aortas. Active stress (forced/areas) was not different. Passive and active length-force relations of portal veins from 16 to 17-week-old SHR and WKY were not different. O2 consumption (JO2) and lactate production (JLA) were studied in aortas and portal veins from 20- to 25-week-old rats. In relaxed aortas, JO2 was 0.63 +/- 0.03 (n = 1) and 0.54 +/- 0.03 (n = 10) mu mol/min per g dry wt in SHR and WKY, respectively (P less than 0.05). On activation by high-K+ solution, JO2 increased with tension in a similar way in both groups. In contrast, JLA, about 0.85 mu mol/min per g, did not differ, and decreased with tension development. JO2 of relaxed portal veins, about 1.5 mu mol/min per g dry wt, and the increase in JO2 with contraction were not different between SHR and WKY, but the JO2-active stress relation was steeper in spontaneous activity than in Kv+ contractures. JLA was similar in SHR and WKY portal veins, about 1 mu mol/min per g, and unlike behavior of the aortas, it increased with tension. Thus it is evident that SHR show increased arterial metabolism, which is not accounted for by an increased energy demand of the contractile system.
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| 17. |
- Arner, Anders, et al.
(författare)
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Influence of ATP, ADP and AMPPNP on the energetics of contraction in skinned smooth muscle
- 1987
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Ingår i: Progress in Clinical and Biological Research. - 0361-7742. ; 245, s. 43-57
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Tidskriftsartikel (refereegranskat)abstract
- The contraction of smooth muscle is influenced by the substrate MgATP and the product MgADP. The effects on force, shortening velocity and ATP-turnover, are consistent with an influence on the kinetics of cross-bridge cycling. Part of these effects are mediated via an influence on the regulation of contraction by myosin light chain phosphorylation. Results from preparations activated by thiophosphorylation, show that MgATP and MgADP also interact directly at the cross-bridge level, and are consistent with MgADP acting as a competitive ATP-analogue. The slow shortening velocity and decreased rate of ATP-induced relaxation from rigor in the presence of MgADP, suggest an inhibition of cross-bridge detachment. The rate of ATP-turnover was decreased in the presence of the nonhydrolyzable ATP-analogue AMPPNP. These results may contribute to the characterization of the biochemical reactions in the structurally organized smooth muscle contractile system. In addition, the influence of MgATP and MgADP on smooth muscle contraction suggest that the concentrations of substrate and products, at the level of the contractile proteins, may constitute important regulatory factors in vivo under conditions, such as hypoxia and ischemia, associated with impaired cellular energy supply.
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| 18. |
- Arner, Anders, et al.
(författare)
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Intracellular calcium in hypertrophic smooth muscle from rat urinary bladder
- 2007
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Ingår i: Scandinavian Journal of Urology and Nephrology. - : Informa UK Limited. - 0036-5599 .- 1651-2065. ; 41:4, s. 270-277
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Tidskriftsartikel (refereegranskat)abstract
- Objective. To explore whether infravesical outlet obstruction is associated with alterations in calcium activation of detrusor smooth muscle. Material and methods. Outlet obstruction was created by partial ligature of the urethra in female rats. Western blotting was performed using an antibody against the cytoplasmatic region of the alpha(1c) subunit of the L- type Ca2(+) channel. Intracellular calcium was measured using Fura-2 in detrusors that had been obstructed for 10 days and activated by high K+ concentrations at different extracellular Ca2(+) concentrations. The rate of force development after rapid opening of L- type Ca2(+) channels was measured in contractions initiated by flash photolysis of nifedipine in Ca2(+) containing depolarizing solution. Results. Bladder weight increased from 6293 to 254943 mg after 10 days of obstruction. Expression of the alpha(1c) subunit increased after 3 days and continued to increase until it was about fourfold greater after 10 days; however, it had not increased further at 6 weeks. This change was reversible after removal of obstruction. Activation with K+ produced a stable force at different extracellular Ca2(+) concentrations, with no difference in response between controls and rats that had been obstructed for 10 days. Intracellular Ca2(+) concentrations were lower in the obstructed group, showing that the calcium sensitivity of the contraction force had increased. The delay between the opening of L- type channels and the onset of contraction was longer in obstructed detrusors. Conclusions. Growth of detrusor muscle following obstruction is accompanied by attenuated calcium transients following activation, despite upregulation of L- type Ca2(+) channels. The Ca2(+) sensitivity of contraction was increased in obstructed detrusors. We suggest that the decreased surface: volume ratio in hypertrophic smooth muscle cells is partly involved in the lowered Ca2(+) transients. The increases in L- type calcium channels and in calcium sensitivity may be compensatory mechanisms.
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| 19. |
- Arner, Anders, et al.
(författare)
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Metabolism and force in hypertrophic smooth muscle from rat urinary bladder
- 1990
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Ingår i: American Journal of Physiology: Cell Physiology. - 1522-1563. ; 258:5 Pt 1, s. 923-932
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Tidskriftsartikel (refereegranskat)abstract
- Ten days of urinary outlet obstruction in the rat induced a threefold increase in bladder weight. Active force of control and hypertrophic bladder muscle strips was measured at varying PO2 levels after high-K+, carbachol, or electrical field stimulation. Highest force output was obtained with carbachol. Force per muscle area was lower in the hypertrophic muscles. The basal rates of oxygen consumption and lactate formation were similar in the two groups. The metabolic tension cost (ATP turnover/active force) was similar in the two groups for activation with high K+ and carbachol. In anoxia the active force decreased, but this was less pronounced in the hypertrophied muscle. Hypertrophied muscle could, in contrast to the controls, maintain a sustained K+ contracture in anoxia. Basal metabolic rates and tension cost were markedly reduced in anoxia for both groups. The lower force per area with unaltered tension cost, in hypertrophic muscles under all experimental conditions, may reflect unaltered intrinsic properties of the contractile system, although the amount of contractile material has decreased relative to cell volume. The increased resistance to anoxia may reflect a metabolic adaptation to impaired oxygen supply to the hypertrophied tissue.
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| 20. |
- Arner, Anders, et al.
(författare)
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Smooth, slow and smart muscle motors.
- 2003
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Ingår i: Journal of Muscle Research and Cell Motility. - 0142-4319. ; 24:2-3, s. 165-173
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Tidskriftsartikel (refereegranskat)abstract
- Smooth muscle is a slow and economical muscle with a large variability in contractile properties. This review describes results regarding the relation between expression of myosin isoforms and the contraction of smooth muscle. The focus of the review is on studies of the organised contractile system in the smooth muscle tissue. The role of the myosin heavy chain variants formed by alternative splicing in the myosin heavy chain tail (SM1, SM2 isoforms) and head (SM-A SM-B isoforms) regions, as well as the role of essential light chains (LC17a, LC17b isoforms) for the variability of contractile properties are discussed. Smooth muscle also has the ability to alter its contractile properties in response to altered functional demands in vivo, e.g. during hypertrophic growth of urinary bladder, intestine, uterus and vessels and in response to altered hormone levels. These alterations involve changes in myosin expression and altered contractile kinetics. Non-muscle myosin has been shown to have a contractile function in some smooth muscle tissues and recent data on the kinetic properties of non-muscle myosin filaments in smooth muscle tissue are described.
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