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H Arheden

Publications and source records attributed to H Arheden.

24 records · Page 2Linked to original sources
PubMed1989

Calcium sensitivity and energetics of contraction in skinned smooth muscle of the guinea pig taenia coli at altered pH.

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.

Adenosine Triphosphate↗
PubMed1988

Cross-bridge behaviour in skinned smooth muscle of the guinea-pig taenia coli at altered ionic strength.

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-gamma-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 mM-phosphocreatine (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. Vmax 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 mumol g-1 min-1. 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.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1987

Force-velocity relation and rate of ATP hydrolysis in osmotically compressed skinned smooth muscle of the guinea pig.

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%).

Adenosine Triphosphate↗
PubMedDate not supplied

Clinical implication of down-scatter in attenuation-corrected myocardial SPECT.

BACKGROUND: Interpretation of myocardial perfusion single photon emission computed tomography (SPECT) studies is hampered by attenuation artifacts. Attenuation correction methods with simultaneous emission and transmission are now commercially available. However, it has been observed in clinical practice that attenuation correction without down-scatter correction in a 1-day rest/stress myocardial perfusion protocol may lead to serious interpretation errors. Therefore the aim of this study was to study errors resulting from down-scatter under realistic conditions, thus providing a background for the assessment of further corrections. METHODS AND RESULTS: Forty-six patients underwent myocardial perfusion scintigraphy in a 1-day technetium 99m-tetrofosmin rest-stress SPECT protocol, with a moving 153Gd line-source device for attenuation correction without down-scatter correction. Short-axis slices were quantified as inferior/anterior, septal/lateral, and apical/remainder count ratios. The changes at rest (350 MBq) and exercise (900 MBq) induced by attenuation correction were studied. Attenuation correction gave differences in apparent perfusion between rest and exercise not seen before correction. The gender differences in inferior-anterior ratio were greatly reduced after correction at rest but remained at exercise. A torso phantom study indicated that these results were due to under-correction at exercise because of down-scatter. CONCLUSIONS: Down-scatter results in an underestimation of attenuation in simultaneous emission and transmission, if not accurately accounted for. Particularly, a high-dose study compared with a low-dose study, as in the 1-day protocol, might cause serious interpretation errors.

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