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- Kruse, M. S., et al.
(författare)
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Recruitment of renal dopamine 1 receptors requires an intact microtubulin network
- 2003
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Ingår i: Pflügers Archiv. - : Springer Science and Business Media LLC. - 0031-6768 .- 1432-2013. ; 445:5, s. 534-539
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Tidskriftsartikel (refereegranskat)abstract
- Renal dopamine1 receptor (D1R) can be recruited from intracellular compartments to the plasma membrane by D1R agonists and endogenous dopamine. This study examines the role of the cytoskeleton for renal D1R recruitment. The studies were performed in LLCPK-1 cells that have the capacity to form dopamine from L-dopa. In approximately 50% of the cells treated with L-dopa the D1R was found to be translocated from intracellular compartments towards the plasma membrane. Disruption of the microtubulin network by noco-dazole significantly prevented translocation. In contrast, depolymerization of actin had no effect. In control cells D1R colocalized with NBD-C-6-ceramide, a trans-Golgi fluorescent marker. This colocalization was disrupted in L-dopa-treated cells. Tetanus toxin, an inhibitor of exocytosis, prevented L-dopa-induced receptor recruitment. L-Dopa treatment resulted in activation of protein kinase C (PKC). To test the functional effect of D1R recruitment, the capacity of D1R agonists to activate PKC was studied. Activation of D1R significantly translocated PKC-alpha from intracellular compartments to the plasma membrane. Disruption of microtubules abolished D1R-mediated - but not phorbol-ester-mediated - translocation of PKC. We conclude that renal D1R recruitment requires an intact microtubulin network and occurs via Golgi-derived vesicles. These newly recruited receptors couple to the PKC signaling pathway.
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- Krustrup, Peter, et al.
(författare)
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Recruitment of fibre types and quadriceps muscle portions during repeated, intense knee-extensor exercise in humans.
- 2004
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Ingår i: Pflügers Archiv. - : Springer Science and Business Media LLC. - 0031-6768 .- 1432-2013. ; 449:1, s. 56-65
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Tidskriftsartikel (refereegranskat)abstract
- To investigate recruitment of slow-twitch (ST) and fast-twitch (FT) muscle fibres, as well as the involvement of the various quadriceps femoris muscle portions during repeated, intense, one-legged knee-extensor exercise, 12 healthy male subjects performed two 3-min exercise bouts at approximately 110% maximum thigh O2 consumption (EX1 and EX2) separated by 6 min rest. Single-fibre metabolites were determined in successive muscle biopsies obtained from the vastus lateralis muscle (n = 6) and intra-muscular temperatures were continuously measured at six quadriceps muscle sites (n = 6). Creatine phosphate (CP) had decreased (P < 0.05) by 27, 73 and 88% in ST fibres and 25, 71 and 89% in FT fibres after 15 and 180 s of EX1 and after 180 s of EX2, respectively. CP was below resting mean-1 SD in 15, 46, 84 and 100% of the ST fibres and 9, 48, 85 and 100% of the FT fibres at rest, after 15 and 180 s of EX1 and after 180 s of EX2, respectively. A significant muscle temperature increase (deltaTm) occurred within 2-4 s at all quadriceps muscle sites. DeltaTm varied less than 10% between sites during EX1, but was 23% higher (P < 0.05) in the vastus lateralis than in the rectus femoris muscle during EX2. DeltaTm in the vastus lateralis was 101 and 109% of the mean quadriceps value during EX1 and EX2, respectively. We conclude that both fibre types and all quadriceps muscle portions are recruited at the onset of intense knee-extensor exercise, that essentially all quadriceps muscle fibres are activated during repeated intense exercise and that metabolic measurements in the vastus lateralis muscle provide a good indication of the whole-quadriceps muscle metabolism during repeated, intense, one-legged knee-extensor exercise.
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- Krustrup, Peter, et al.
(författare)
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The slow component of oxygen uptake during intense, sub-maximal exercise in man is associated with additional fibre recruitment.
- 2004
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Ingår i: Pflügers Archiv. - : Springer Science and Business Media LLC. - 0031-6768 .- 1432-2013. ; 447:6, s. 855-66
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Tidskriftsartikel (refereegranskat)abstract
- Single muscle fibre metabolites and pulmonary oxygen uptake (VO2) were measured during moderate and intense, sub-maximal exercise to test the hypothesis that additional fibre recruitment is associated with the slow component of VO2. Seven healthy, male subjects performed 20 min moderate (MOD, approximately 50% of VO(2,max)) and intense (INT, approximately 80% VO(2,max)) cycling at 70 rpm. Glycogen content decreased significantly in type I and IIa fibres during INT, but only in type I fibres during MOD. During INT, creatine phosphate (CP) content decreased significantly both in types I and II fibres in the first 3 min (DeltaCP: 16.0+/-2.7 and 16.8+/-4.7 mmol kg(-1) d.w., respectively) and in the next 3 min (DeltaCP: 16.2+/-4.9 and 25.7+/-6.7 mmol kg(-1) d.w., respectively) with no further change from 6-20 min. CP content was below the pre-exercise level (mean-1 SD) in 11, 37, 70 and 74% of the type I fibres after 0, 3, 6 and 20 min of INT, respectively, and in 13, 45, 83 and 74% of the type II fibres. During INT, VO2 increased significantly by 6+/-1 and 4+/-1% in the periods 3-6 and 6-20 min, respectively (Delta VO(2,(6-3 min)): 0.14+/-0.02 l min(-1)), whereas VO2 was unchanged from 3 to 20 min of MOD. Exponential fitting revealed a slow component of VO2 during INT that appeared after approximately 2.6 min and amounted to 0.24 l min(-1). The present study demonstrates that additional type I and II fibres are recruited with time during intense sub-maximal exercise in temporal association with a significant slow component of VO2.
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- Larsson-Nyrén, Gerd, et al.
(författare)
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Perchlorate stimulates insulin secretion by shifting the gating of L-type Ca2+ currents in mouse pancreatic B-cells towards negative potentials
- 2001
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Ingår i: Pflügers Archiv. - : Springer Science and Business Media LLC. - 0031-6768 .- 1432-2013. ; 441:5, s. 587-595
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Tidskriftsartikel (refereegranskat)abstract
- The effects of the chaotrophic anion perchlorate (ClO4-) on glucose-induced electrical activity, exocytosis and ion channel activity in mouse pancreatic B-cells were investigated by patch-clamp recordings and capacitance measurements. ClO4- stimulated glucose-induced electrical activity and increased the action potential frequency by 70% whilst not affecting the membrane potential when applied in the presence of a subthreshold concentration of the sugar. ClO4- did not influence ATP-dependent K (KATP) channel activity and voltage-gated delayed K+ current. Similarly, ClO4- had no effect on Ca2+-dependent exocytosis. The stimulation of electrical activity and insulin secretion was instead attributable to an enhancement of the whole-cell Ca2+ current. This effect was particularly pronounced at voltages around the threshold for action potential initiation and a doubling of the current amplitude was observed at -30 mV. This was due to a 7-mV shift in the gating of the Ca2+ current towards negative voltages. The action of ClO4- was more pronounced when added in the presence of 0.1 mM BAY K8644, whereas no stimulation was observed when applied at a maximal concentration of the agonist (1 mM). Single-channel recordings revealed that the effect of ClO4- on whole-cell currents was principally due to a 60% increase in the mean duration of the long openings and the number of active channels. We propose that ClO4- stimulates insulin secretion and electrical activity by exerting a BAY K8644-like action on Ca2+ channel gating.
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