| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- Arner, Anders, et al.
(författare)
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Structural and mechanical adaptations in rat aorta in response to sustained changes in arterial pressure
- 1984
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772. ; 122:2, s. 119-126
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Tidskriftsartikel (refereegranskat)abstract
- Structural and mechanical adaptations in response to sustained changes in arterial pressure were studied on abdominal aorta of the male rat. Two models were used: 1. Aortic ligature (L), immediately below the renal arteries producing hypotension distal to the knot (duration before sacrifice 6 weeks or 3 months). 2. One-clip renal hypertensive rats (H) (duration 6 weeks). Normotensive sham-operated rats (C) served as controls. At sacrifice mean tail artery pressure was L: 58 +/- 1, C: 110 +/- 3, and H: 163 +/- 5 mmHg (SE, N=6). Segments of abdominal aorta were mounted in vitro for determination of their length-tension relations (activation: High-K+ solution with 2.5 mM Ca2+). At end of experiments the vessels were supramaximally stimulated at optimal circumference (1o) for active force (activation: High-K+ solution with 10 mM Ca2+, and 10(-5) M noradrenaline), and then fixated for light and electron microscopy. Passive and active length-tension relations were shifted towards lower and higher circumference values for hypo- and hypertensive vessels, respectively. The 1o values were L: 3.60 +/- 0.13, C: 4.44 +/- 0.19, and H: 4.91 +/- 0.29 mm. The media thickness at 1o was reduced in L: 56.0 +/- 3.3, and increased in H: 81.3 +/- 2.4 compared to C: 73.4 +/- 1.8 micron. Maximal active wall stress was L: 46.6 +/- 9.8, C: 74.2 +/- 7.0, and H: 83.8 +/- 7.7 mN/mm2. Intracellular volume (ICV) in the media was L: 30 +/- 2, C: 45 +/- 3, and H: 44 +/- 1% (n=4 for each).
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| 5. |
- Chen, Y, et al.
(författare)
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Increase in insulin-like growth factor I in hypertrophying smooth muscle
- 1994
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Ingår i: American Journal of Physiology - Endocrinology and Metabolism. - 1522-1555. ; 266:2 Pt 1, s. 224-229
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Tidskriftsartikel (refereegranskat)abstract
- The present study focuses on the role of the insulin-like growth factor (IGF) system in the development of smooth muscle hypertrophy. Hypertrophy was initiated by partial ligation of portal vein or urethra in female Sprague-Dawley rats weighing approximately 220 g. Levels of mRNA were analyzed by solution hybridization. Seven days after ligation, the wet weight of the portal vein was increased about threefold and the concentration of IGF-I mRNA was increased fourfold. The bladder wet weight was increased twofold 3 days after ligation and fourfold 10 days after ligation. IGF-I mRNA in the bladder was elevated 3-fold after 3 days and 2.5-fold after 10 days, whereas IGF binding protein 2 mRNA was increased approximately 2-fold after 3 days and 5-fold after 10 days. IGF-I receptor mRNA in the hypertrophying bladder remained unchanged. Increased levels of IGF-I were demonstrated with immunohistochemistry in both hypertrophying portal vein and urinary bladder. The results show a specific increase in IGF-I mRNA as well as an increased IGF-I immunoreactivity during hypertrophy of smooth muscle, which suggests that the local IGF-system may play a role in smooth muscle hypertrophy.
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| 6. |
- Lindqvist, Anders, et al.
(författare)
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Long-term effects of Ca(2+) on structure and contractility of vascular smooth muscle
- 1999
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Ingår i: American Journal of Physiology: Cell Physiology. - 1522-1563. ; 277:1, s. 64-73
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Tidskriftsartikel (refereegranskat)abstract
- Culture of dispersed smooth muscle cells is known to cause rapid modulation from the contractile to the synthetic cellular phenotype. However, organ culture of smooth muscle tissue, with maintained extracellular matrix and cell-cell contacts, may facilitate maintenance of the contractile phenotype. To test the influence of culture conditions, structural, functional, and biochemical properties of rat tail arterial rings were investigated after culture. Rings were cultured for 4 days in the absence and presence of 10% FCS and then mounted for physiological experiments. Intracellular Ca(2+) concentration ([Ca(2+)](i)) after stimulation with norepinephrine was similar in rings cultured with and without FCS, whereas force development after FCS was decreased by >50%. The difference persisted after permeabilization with beta-escin. These effects were associated with the presence of vasoconstrictors in FCS and were dissociated from its growth-stimulatory action. FCS treatment increased lactate production but did not affect ATP, ADP, or AMP contents. The contents of actin and myosin were decreased by culture but similar for all culture conditions. There was no effect of FCS on calponin contents or myosin SM1/SM2 isoform composition, nor was there any appearance of nonmuscle myosin. FCS-stimulated rings showed evidence of cell degeneration not found after culture without FCS or with FCS + verapamil (1 microM) to lower [Ca(2+)](i). The decreased force-generating ability after culture with FCS is thus associated with increased [Ca(2+)](i) during culture and not primarily caused by growth-associated modulation of cells from the contractile to the synthetic phenotype.
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| 7. |
- Malmqvist, Ulf, et al.
(författare)
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Contractile and cytoskeletal proteins in smooth muscle during hypertrophy and its reversal
- 1991
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Ingår i: American Journal of Physiology: Cell Physiology. - 1522-1563. ; 260:5, s. 1085-1093
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Tidskriftsartikel (refereegranskat)abstract
- Hypertrophy of rat urinary bladder smooth muscle was induced by partial urethral obstruction. Bladder weight increased from 70 to 240 mg after 10 days and to 700 mg after 7 wk. Removal of the obstruction after 10 days caused a regression of bladder weight to 130 mg. The relative volume of smooth muscle in the bladder wall increased during hypertrophy. The concentration of myosin in the smooth muscle cells decreased in 10-day hypertrophied bladders, whereas the concentration of actin was unchanged. The actin-myosin ratio was 2.3 in controls, 3.3 in 10-day obstructed bladders, and 2.9 in 7-wk obstructed bladders. After removal of obstruction, the ratio was normalized. Two isoforms of myosin heavy chains were identified (SM1 and SM2). The relative amount of SM2 decreased during hypertrophy. The relative proportion of actin isoforms (alpha, beta, and gamma) was altered toward more gamma and less alpha. These changes were reversible upon removal of the obstruction. Desmin was the dominating intermediate filament protein. The concentration of desmin and filamin increased in the hypertrophic bladders. The increased desmin-actin and filamin-actin ratios in obstructed bladders were normalized after removal of the obstruction. The results suggest that the turnover of contractile and cytoskeletal proteins is fast and can be regulated in response to changes in the functional demands in smooth muscle.
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| 8. |
- Malmqvist, Ulf, et al.
(författare)
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Cytoskeletal and contractile proteins in detrusor smooth muscle from bladders with outlet obstruction--a comparative study in rat and man
- 1991
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Ingår i: Scandinavian Journal of Urology and Nephrology. - : Informa UK Limited. - 0036-5599 .- 1651-2065. ; 25:4, s. 261-267
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Tidskriftsartikel (refereegranskat)abstract
- Detrusor biopsies were obtained from patients with urinary outlet obstruction due to prostatic enlargement and from age-matched control patients. The relative amounts of actin and myosin and their isoforms, as well as desmin and filamin were determined and compared with corresponding results from bladders from control rats and rats with 10 days of experimental outlet obstruction of the urinary bladder. In the human control detrusor the actin/myosin ratio was similar to that in the control rat. The isoform distribution of the myosin heavy chains differed between man and rat. In the biopsies from the patients with outlet obstruction and in the obstructed rat bladders the actin/myosin ratio was increased. A change in the myosin heavy chain distribution in the obstructed bladders was observed for both species. The filamin/actin ratio increased significantly in the obstructed rat bladders and tended to increase in the obstructed human bladders. Desmin was the dominating intermediate filament protein. The desmin/actin ratio increased in obstructed bladders in man and in rat.
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| 9. |
- Malmqvist, Ulf, et al.
(författare)
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Mechanics and Ca(2+)-sensitivity of human detrusor muscle bundles studied in vitro
- 1991
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772. ; 143:4, s. 373-380
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Tidskriftsartikel (refereegranskat)abstract
- Mechanical properties of isolated smooth muscle strips from human urinary bladder were investigated in vitro. Bladder tissue was obtained from tumour-free wall regions of bladders from male patients undergoing cystectomy for bladder carcinoma. In intact muscle strips, activated with high-K+ solution, half-maximal force occurred at about 0.9 mM extracellular [Ca2+]. The length-active force relation was determined and the muscle strips were fixed for light and electron microscopy at optimal length for active force (1o). The maximal active force per unit smooth muscle cross-sectional area was 208 +/- 49 mN/mm2, n = 6. Chemically skinned preparations were obtained by treatment with triton X-100. These preparations had a steep [Ca2+]-force relation in the micromolar range which was influenced by calmodulin. The skinned preparations could be maximally activated by irreversible thiophosphorylation of the regulatory light chains. The force-velocity relation was determined in the maximally activated skinned muscle at 22 degrees C at 0.51o. When the muscle was shortened by 10%, force was reduced by 35% whereas the maximal shortening velocity was little affected.
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| 10. |
- 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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