| 1. |
- Ivanova, L N, et al.
(författare)
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Decrease in the response to ADH of the rat kidney as a result of early postnatal treatment with cortisol.
- 1987
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Ingår i: Pflügers Archiv. - 0031-6768 .- 1432-2013. ; 408:4, s. 328-32
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Tidskriftsartikel (refereegranskat)abstract
- Wistar rats were injected just once, intraperitoneally with cortisol (1 microgram/g) or saline at the age of 5 days. The cortisol-treated rats did not differ significantly in the (U/P)osm ratio from the saline-treated controls before 15 days of life. Their response to ADH was distinct but weaker than in the saline controls aged 30 days. This reduced response persisted to 60 days of life. In the collecting tubule fragments, (3H)AVP specific binding was lower in the cortisol-treated rats than in the controls at the age of 20 and 60 days. There was no (3H)AVP specific binding in the proximal convoluted tubules in the cortisol- and saline-injected rats of both ages. The ontogenetic patterns of cAMP specific binding in the papillary cytosolic fraction were different: the early increase in cAMP binding was protracted in the cortisol-treated rats, and no peak appeared at the age of 25 days. Cytosolic protein kinase activity was lower, no peak appeared at 30 days, no activation of protein kinase occurred to the end of weaning in the cortisol-treated rats. The difference between the cortisol and saline groups was abolished by day 30. The interference of cortisol with the ontogenetic changes in AVP binding capacity and cAMP-dependent protein kinase appears to be a plausible cause of the altered development of the response to ADH.
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| 2. |
- 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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| 3. |
- Hellstrand, Per, et al.
(författare)
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Myosin light chain phosphorylation and the cross-bridge cycle at low substrate concentration in chemically skinned guinea pig Taenia coli
- 1985
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Ingår i: Pflügers Archiv. - 0031-6768. ; 405:4, s. 323-328
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Tidskriftsartikel (refereegranskat)abstract
- Force-velocity relations, rate of ATP turnover (JATP), and phosphorylation of the 20,000 D myosin light chains (LC20) were measured in chemically skinned guinea pig Taenia coli. Relative LC20 phosphorylation at 3.2 mM MgATP was 17% in relaxed tissues at pCa 9, and increased with force at increasing [Ca2+] to a maximum of 67% at pCa 4.5. Force at pCa 4.5 was dependent on the MgATP concentration with a half-maximal response at about 0.1 mM. At 0.1 mM MgATP LC20 phosphorylation at pCa 4.5 was 38%. Both JATP and the maximal shortening velocity (Vmax) were reduced in 0.1 mM MgATP, to 32% and 43%, respectively, of their values at 3.2 mM MgATP. Low-MgATP thus inhibits both LC20 phosphorylation and the extent and rate of cross-bridge interaction. High levels of LC20 phosphorylation, independent of Ca2+ and MgATP concentrations, were obtained by treatment with ATP-gamma-S. Maximal force at 3.2 mM MgATP after LC20 thiophosphorylation was unchanged, whereas halfmaximal force occurred at 0.065 mM MgATP after thiophosphorylation, compared to 0.13 mM after activation by Ca2+. The contraction in thiophosphorylated preparations at low-MgATP (0.1 mM) was associated with submaximal Vmax (60%) and JATP (27%). The results show that LC20 phosphorylation is correlated with the degree of force development in the Ca2+ activated contraction, both when Ca2+ and MgATP concentrations are varied. The reduced force and rate of crossbridge turnover in low MgATP are however primarily mediated by an influence of MgATP on the cross-bridge cycle, which is separate from the effect on LC20 phosphorylation.
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| 4. |
- Sparrow, Malcolm P, et al.
(författare)
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Myosin composition and functional properties of smooth muscle from the uterus of pregnant and non-pregnant rats
- 1988
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Ingår i: Pflügers Archiv. - 0031-6768. ; 412:6, s. 624-633
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Tidskriftsartikel (refereegranskat)abstract
- The myosin heavy chain stoichiometry and the force-velocity relation have been determined in the myometrium of the non-pregnant and pregnant rat. The relative proportions of the slower migrating heavy chain (MHC1) greatly exceeded that of the faster migrating heavy chain (MHC2) as shown by electrophoresis on SDS 4%-polyacrylamide gels. The ratios of MHC1/MHC2 were 2.2/1 in the non-pregnant rats, 2.6/1 in the pregnant rat, and contrasted with 0.8/1 in the rat portal vein. This stoichiometry was unchanged by extracting the myosin from the smooth muscle as native myosin in a salt extract, as dissociated myosin using sodium dodecyl sulphate (SDS) or by isolating the native myosin first by a non-dissociating (pyrophosphate) electrophoresis step and subsequently analysing the protein bands on the SDS 4%-polyacrylamide gel. Although the unequal proportions of the heavy chains suggested the possibility that the native myosin molecule may be arranged as homodimeric heavy chains, no evidence for or against the existence of native myosin isoforms could be obtained by electrophoresing native myosin extracts on pyrophosphate-polyacrylamide gels. The force-velocity relations of the intact electrically stimulated myometrium from the non-pregnant and pregnant rats gave isometric force of 45 and 135 mN/mm2 and Vmax of 0.71 and 0.52 lengths/s (37 degrees C) when measured at 95% of optimal length, whereas in chemically skinned uterine strips at 22 degrees C Vmax was 0.09 and 0.13 lengths/s, respectively. The length-force relationship was of similar shape in the non-gravid and gravid skinned tissues. The energetic tension cost (ATP-turnover/active stress) in skinned fibres was also similar. The mechanical and metabolic characteristics of the gravid and non-gravid uterus found in the present study do not suggest an obvious difference in the intrinsic properties of the myosin, although significant functional alterations in the tissue appear during pregnancy. This corresponds to the lack of a difference in the pattern of the heavy chains.
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| 5. |
- Tågerud, Sven, et al.
(författare)
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Effects of botulinum toxin induced muscle paralysis on endocytosis and lysosomal enzyme activities in mouse skeletal muscle
- 1986
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Ingår i: Pflügers Archive European Journal of Physiology. - 0031-6768. ; 407:3, s. 275-278
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Tidskriftsartikel (refereegranskat)abstract
- The effects of botulinum toxin (type A) induced muscle paralysis on endocytosis and lysosomal enzyme activities in skeletal muscle were compared with the effects of surgical denervation. Muscle atrophy, measured as decrease in total muscle protein content, was as large or larger after botulinum toxin treatment as after denervation. Endocytic activity, measured as the in vitro uptake of horseradish peroxidase, and the specific activities of the lysosomal enzymes N-acetyl--d-glucosaminidase and cathepsin D were all increased six days after denervation. Only the specific activity of cathepsin D was increased six days after botulinum toxin poisoning. The uptake of horseradish peroxidase and the specific activity of N-acetyl--d-glucosamidase were also increased eleven days after poisoning. Transverse sections of eleven days botulinum poisoned muscles from animals injected with horseradish peroxidase showed fibres with dense peroxidase staining similar to those seen in denervated muscle although they seemed to occur less frequently.The results show that increases in endocytic activity and lysosomal enzyme activities may occur in skeletal muscle without the presence of degenerating axons. The differences in effects of surgical denervation and botulinum toxin induced paralysis are discussed in terms of what is known about the mechanism of action of botulinum toxin and the possible functional roles of the two lysosomal enzymes studied.
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