| 1. |
- Birnir, Bryndis, et al.
(författare)
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Voltage-clamp studies of the Na+/glucose cotransporter cloned from rabbit small intestine.
- 1991
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Ingår i: Pflügers Archiv. - 0031-6768 .- 1432-2013. ; 418:1-2, s. 79-85
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Tidskriftsartikel (refereegranskat)abstract
- Inward Na+ currents associated with the cloned intestinal Na+/glucose cotransporter expressed in Xenopus oocytes have been studied using the two-microelectrode voltage-clamp method. The steady-state current/voltage relations showed voltage-dependent (Vm from +20 to -75 mV) and relatively voltage-independent (Vm from -75 to -150 mV) regions. The apparent Imax for Na+ and glucose increased with negative membrane potentials, and the apparent K0.5 for glucose (K(Glc)0.5) depended on Vm and [Na]o. Increasing [Na]o from 7 to 110 mmol/l had the same effect in decreasing K(Glc)0.5 from 0.44 to 0.03 mmol/l as increasing the Vm from -40 to -150 mV. The I/V curves under saturating conditions (20 mmol/l external sugars and 110 mmol/l [Na]o) were identical for D-glucose, D-galactose, alpha-methyl D-glucopyranoside and 3-O-methyl D-glucoside. The specificity of the cotransporter for sugars was: D-glucose, D-galactose, alpha-methyl D-glucopyranoside greater than 3-O-methyl D-glucoside much greater than D-xylose greater than D-allose much greater than D-mannose. Ki for phlorizin (approximately 10 mumol/l) was independent of Vm at saturating [Na]o. We conclude that a variety of sugars are transported by the cloned Na+/glucose cotransporter at the same maximal rate and that membrane potential affects both the maximal current and the apparent K0.5 of the cotransporter for Na+ and glucose.
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| 2. |
- Boels, P J, et al.
(författare)
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Structure and mechanics of growing arterial microvessels from hypertrophied urinary bladder in the rat
- 1994
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Ingår i: Pflügers Archiv. - 0031-6768. ; 426:6, s. 506-515
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Tidskriftsartikel (refereegranskat)abstract
- Rat bladder hypertrophy, induced by a partial ligation of the urethra, was used to study the accompanying changes of microvascular smooth muscle mechanics, pharmacology and morphology. A segment of a microarterial vessel to the bladder was taken from a defined anatomical location and studied in a wire myograph in vitro at the length for maximal isometric force development (Lmax). After 10 days of ligation, bladder hypertrophy resulted in a microvascular growth response compared to non-operated controls which was characterized by (i) an increase of the calculated diameter at Lmax from 134 +/- 5 microns to 222 +/- 19 microns; (ii) an increase of the media thickness from 22.4 +/- 1.9 microns to 32.2 +2- 3.0 microns; (iii) an increase of the active tension from 1.42 +/- 0.28 mN/mm to 3.06 +/- 0.33 mN/mm; (iv) no change of the wall/lumen ratio (from 0.83 +/- 0.10 to 0.79 +/- 0.15). Normalized length/force relations (active, passive and total) did not differ significantly between microarteries from control and hypertrophic bladders. Microvascular smooth muscle growth was also associated with a decreased sensitivity to K(+)-induced depolarization and an increased sensitivity to alpha 1-adrenergic stimulation. No differences were noted regarding the Ca2+ sensitivity of force during K(+)-induced depolarization. The results suggest that microvascular growth (1) is immediately and positively influenced by the organ growth; (2) results in a functional resetting of the microvascular segments towards larger diameters without gross morphological or mechanical alterations; and (3) is accompanied by pharmacological alterations of the smooth muscle reactivity.
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| 3. |
- Himpens, B, et al.
(författare)
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Free cytosolic calcium during spontaneous contractions in smooth muscle of the guinea-pig mesotubarium
- 1990
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Ingår i: Pflügers Archiv. - 0031-6768. ; 417:4, s. 404-409
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Tidskriftsartikel (refereegranskat)abstract
- The free intracellular calcium ion concentration ([Ca2+]i) was measured simultaneously with isometric force in strips of guinea-pig mesotubarium using the Fura-2 technique. During the relaxed period (5-15 min) between spontaneous contractions [Ca2+]i continues to decrease after full mechanical relaxation to reach a minimal level of 86 +/- 8 nM (n = 9) just before the start of the next contraction. During the spontaneous contractions (5-15 min) [Ca2+]i reached a maximum of 211 +/- 19 nM and then oscillated between 155 +/- 16 nM and 194 +/- 9 nM. Increased extracellular Ca2+ concentration to 10 mM from the standard concentration of 1.5 mM caused a decreased frequency of spontaneous contractions and an increase in [Ca2+]i both in the relaxed and contracted states. In 10 mM extracellular Ca2+, addition of AlF4-, as 1 mM NaF + 10 microM AlCl3, caused a sustained increase in [Ca2+]i and maintained force. Addition of verapamil (10 microM) in this situation decreased [Ca2+]i to the resting level. The results suggest that the cyclic appearance of trains of action potentials is related to variation in [Ca2+]i, possibly via inactivation of Ca2(+)-dependent K+ channels.
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| 4. |
- Lydrup, M L, et al.
(författare)
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Effects of extracellular K+ and Ca2+ on membrane potential, contraction and 86Rb+ efflux in guinea-pig mesotubarium
- 1990
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Ingår i: Pflügers Archiv. - 0031-6768. ; 415:6, s. 664-670
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Tidskriftsartikel (refereegranskat)abstract
- The effects of varying extracellular concentrations of K+ and Ca2+ [K+]o and [Ca2+]o on force development and membrane potential were investigated in the guinea-pig mesotubarium. At [K+]o up to 40 mM, spontaneous action potentials were present, while higher [K+]o gave sustained contractures at a stable membrane potential (-24 to -12 mV for [K+]o from 60 to 120 mM). Tension decreased successively with increasing [K+]o from 30 to 120 mM. The relaxing potency of the dihydropyridine Ca2+ antagonist, felodipine, increased as the membrane was depolarized with increasing [K+]o and action potentials ceased. These results are compatible with the existence of Ca2+ channels showing voltage-dependent affinity with dihydrophyridines. Increasing [Ca2+]o from 2.5 to 10 mM caused membrane hyperpolarization by about 11 mV and was accompanied by a lower frequency of spontaneous contractions and a longer duration of the relaxation between contractions. 86Rb+ efflux measurements in 60 mM K+ in the absence and presence of felodipine revealed a Ca2(+)-dependent component of the voltage-activated efflux. In normal solution (5.9 mM K+), efflux in the presence of felodipine was similar to the minimal value during normal spontaneous activity. The results indicate regulation of the permeability of K+ channels by the intracellular Ca2+ concentration ([Ca2+]i) and suggest participation of such channels in the generation of the regularly occurring bursts of action potentials characteristic of spontaneous activity in the mesotubarium.
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| 5. |
- Lydrup, M L, et al.
(författare)
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Paradoxical decrease in cytosolic calcium with increasing depolarization by potassium in guinea-pig mesotubarium smooth muscle
- 1992
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Ingår i: Pflügers Archiv. - 0031-6768. ; 420:5-6, s. 428-433
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Tidskriftsartikel (refereegranskat)abstract
- The free intracellular Ca2+ concentration ([Ca2+]i) was measured simultaneously with isometric force in strips of guinea-pig mesotubarium using the Fura-2 technique. [Ca2+]i and force were maximal at a relatively low (30 mM) concentration of extracellular K+ ([K+]o), and declined at 90 and 140 mM K+. Plateau values of both [Ca2+]i and force were higher in the presence of 5.10(-6) M ryanodine, indicating that the sarcoplasmic reticulum (SR) contributes to the decline with depolarization. Force and [Ca2+]i at 90 mM K+ were both lower then the high-K+ solution was applied after a period in 30 mM K+ than after a period in normal solution (5.9 mM K+), consistent with inactivation of Ca2+ channels during prolonged depolarization. Addition of carbachol to the depolarized muscle caused a maintained increase in force without maintained increase in [Ca2+]i. We conclude that the decrease in force at increased [K+]o (the "calcium-potassium paradox") is due to a membrane-potential-mediated decrease in [Ca2+]i and, to a lesser extent, to desensitization of the contractile-regulatory apparatus to Ca2+.
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| 6. |
- Malmqvist, Ulf, et al.
(författare)
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Correlation between isoform composition of the 17 kDa myosin light chain and maximal shortening velocity in smooth muscle
- 1991
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Ingår i: Pflügers Archiv. - 0031-6768. ; 418:6, s. 523-530
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Tidskriftsartikel (refereegranskat)abstract
- The relation between the isoform distribution of the myosin 17 kDa essential light chain (LC17) and the mechanical properties of smooth muscle was investigated. The relative content of the basic (LC17b) and acidic (LC17a) isoelectric variants of the 17 kDa myosin light chain was determined in different mammalian smooth muscle tissues. The relative content of LC17b varied between muscles: rabbit rectococcygeus 0%, rabbit trachea 5%, guinea-pig taenia coli 21%, rat uterus 38%, rabbit aorta 56% and rat aorta 60%. The rate of tension development was determined following photolysis of caged-adenosine triphosphate (ATP) in skinned fibres activated with thiophosphorylation of the regulatory light chains. The half-time for force development was 0.67 s in rabbit rectococcygeus, 1.6 s in rabbit trachea, 1.13 s in guinea-pig taenia coli and 1.38 s in rabbit aorta. The maximal shortening velocity (Vmax) was determined with the isotonic quick release technique in skinned fibre preparations activated with thiophosphorylation. Vmax was 0.25 muscle lengths per second (ML/s) in rabbit rectococcygeus, 0.24 ML/s in rabbit trachea, 0.17 ML/s in guinea-pig taenia coli, 0.11 ML/s in rat uterus and 0.03 ML/s in rabbit aorta. The range of variation in Vmax between muscles was larger than in the half-time for force development. The inverse relationship between Vmax and the relative content of LC17b in the investigated muscles suggests that the type of essential myosin light chain influences the Vmax in smooth muscle.
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| 7. |
- Malmqvist, Ulf, et al.
(författare)
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Lactate dehydrogenase activity and isoform distribution in normal and hypertrophic smooth muscle tissue from the rat
- 1991
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Ingår i: Pflügers Archiv. - 0031-6768. ; 419:3-4, s. 230-234
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Tidskriftsartikel (refereegranskat)abstract
- The lactate dehydrogenase (LDH) activity and isoform distribution of LDH were investigated in tissue samples from the rat portal vein, aorta and urinary bladder. In addition, samples were obtained from hypertrophic urinary bladder. The total LDH activity per unit smooth muscle volume was higher in the urinary bladder compared to that in portal vein and aorta. Five LDH isoforms, reflecting different combinations of the two polypeptide chains denoted H and M, could be separated by agarose gel electrophoresis. The aorta contained more of the H form compared to the portal vein and urinary bladder. This difference suggests that the aorta, which is a slow smooth muscle, is more adapted for aerobic metabolism than the faster muscles of portal vein and urinary bladder. In the hypertrophic urinary bladder a shift in LDH isoform pattern towards less of the H form was found, which correlates with a better maintenance of contraction in anoxia in this type of hypertrophic smooth muscle.
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