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| 2. |
- Fändriks, L, et al.
(författare)
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Sympatho-adrenergic inhibition of basal and acid-induced changes in duodenal motility, mucosal net fluid and alkaline secretion in the anaesthetized cat
- 1995
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Ingår i: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 153:3, s. 211-219
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Tidskriftsartikel (refereegranskat)abstract
- Experiments were performed on chloralose anaesthetized cats. A 2-cm segment of the proximal duodenum was isolated between two luminally situated balloons and perfused with isotonic saline containing [14C]-PEG 4000 as a non-absorbable marker. The perfusate was analysed with regard to alkalinity (back titration) and concentration of marker (liquid scintillation). Net alkalinization and net fluid transport were calculated with conventional equations. Motor activity in the duodenal wall was recorded as changes in volume of the proximal balloon. In presence of sympathetic neural activity (spontaneous or electrically stimulated) basal motor activity and mucosal alkaline secretion was low and increased minimally in response to luminal HCl (30 mM). Net fluid transport was in an absorptive state and shifted to a small secretion upon the acid-exposure. Subsequent to bilateral acute splanchnicotomy, or the administration of the adrenolytic guanethidine (3-4 mg kg-1, i.v.), spontaneous duodenal contractions occurred and the alkaline secretion was increased. Furthermore, both parameters were then markedly stimulated by luminal perfusion with 30 mM HCl. Basal net fluid transport was zero and turned into secretion upon the acid-exposure. No morphological changes of the duodenal surface epithelium could be detected. The study demonstrates the existence of splanchnic nerve-mediated, adrenergic inhibition of basal, as well as of acid-induced duodenal motility, fluid and alkaline secretion.
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| 3. |
- Hellstrand, Per, et al.
(författare)
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Analysis of the length response to a force step in smooth muscle from rabbit urinary bladder
- 1979
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772. ; 106:2, s. 221-238
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Tidskriftsartikel (refereegranskat)abstract
- Responses to isotonic quick release of AC-stimulated smooth muscle strips from rabbit urinary bladder were analysed. Releases were performed at the peak of contraction and at a preset tension level in the contraction and relaxation phase. In other expts. responses at 37 degrees C and 27 degrees C were compared. The length response always consisted of 3 parts: (1) elastic recoil, (2) rapid length change (isotonic transient), (3) steady length change. Qualitatively, phases (1)-(3) could be distinguished also in responses to isotonic quick stretch. The immediate elastic recoils, phase (1), were described by exponential stress-strain relations. Stiffness was found to be somewhat lower during relaxation than during contraction. No effect of temperature on the elastic recoil was seen. The initial velocity in phase (2) was 2-3 times greater than the velocity 100 ms after release. By means of computer analysis of the length records during phases (2) and (3) two decaying exponential processes with widely different time constants could be separated. The time constant of the faster process was of the order of 15-30 ms at 37 degrees C. It decreased with increasing force steps and with increasing temperature. The amount of shortening associated with this process was correlated with the size of the force step, reaching a maximum of about 1.2% of the muscle length. The shortening velocities in phase (3), measured 100 ms after release, were described by Hill's equation. Vmax in the rising part and at the peak of contraction were 0.7 and 0.6 L/s respectively at 37 degrees C. Lower values were found during relaxation and at 27 degrees C. We suggest that part of the elastic recoil in phase (1) occurs in structures associated with the individual cross-bridges, that phase (2) is dominated by a change in the distribution of conformations of bridges in the attached position and that the shortening rate in phase (3) is determined by the entire cycle of events during turnover of bridges after the muscle has adapted to the new load. Observations on the force response to length steps and on shifts from isometric to afterloaded isotonic contraction and vice versa are consistent with this interpretation.
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| 5. |
- Hellstrand, Per, et al.
(författare)
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Mechanical, electrical, and biochemical effects of hypoxia and substrate removal on spontaneously active vascular smooth muscle
- 1977
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772. ; 100:1, s. 69-83
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Tidskriftsartikel (refereegranskat)abstract
- Effects of hypoxia and glucose-free solution on the isolated rat portal vein were studied. Decrease of extracellular PO2 below 50 mm Hg caused graded inhibition of spontaneous mechanical activity; below 7 mm Hg, inhibition was complete in most preparations. Contracture force of depolarized portal vein was less sensitive to decreases in PO2. Responses to noradrenaline at all concentrations were markedly depressed at extreme hypoxia. Sucrose-gap experiments showed that hypoxia reduced the spontaneous electrical spike discharge. Mean tissue contents of PCr, ATP and glycogen (expressed as glucose) were 3.02, 2.47 and 5.07 micromol/g cell wt. in spontaneously active control muscles and 1.07, 1.65 and 1.83 after 20 min anoxia. Physiological variations in PO2 may influence myogenic activity of vascular smooth muscle largely through an action at the membrane level and this mechanism may participate in local blood flow control. Caculations indicated that the graded response to hypoxia in the present in vitro experiments was not due to diffusion limitation. Spontaneous mechanical activity was relatively well maintained even after prolonged exposure to glucose-free solution, whereas the responses to K+ and noradrenaline were markedly suppressed. Electrophysiological recordings during spontaneous activity indicated desynchronization and impaired conduction. PCr and ATP were maintained at control levels and glycogen reduced by 50 per cent after 2 h in glucose-free medium. Indications of the use of amino acids (glutamate) as substrate under these conditions were obtained.
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| 6. |
- Hellstrand, Per, et al.
(författare)
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The force-velocity relation in phasic contractions of venous smooth muscle
- 1975
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772. ; 93:2, s. 157-166
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Tidskriftsartikel (refereegranskat)abstract
- The force-velocity relation of the rat portal vein has been studied during regular spontaneous contractions induced by elevated levels of [K-+]O AND [Ca-2+]o. No satisfactory description of the force-velocity relation was obtained by measuring shortening velocity in afterloaded isotonic contractions. Therefore the method of isotonic quick release was used, as this permits mechanical studies at specified instants of the contraction-relaxation cycle. The temporal development of the force-velocity relation in the phasic response was investigated. During a time interval in the rising phase of the contraction, at about the time for maximal dP/dt, the force-velicity curves were practically identical, suggesting a plateau in the intensity of active state. At later stages of the twitch the curves were progressively displaced towards the origin, the intercepts on both the force and the velocity axis becoming smaller. At the time of the isometric peak the maximal shortening velocity had declined relatively more than the isometric force. This is presumably caused by inhomogeneous activation of the muscle at the beginning of relaxation, The maximal force-velocity relation in the rising phase of the contraction can be described by Hill's (1938) equation with the following parameters (at 37 degrees tc): a/Po = 0.73 plus or minus 0.04, b = 0.54 plus or minus 0.04 lengths/s, Vmax = 0.74 plus or minus 0.02 lengths/s (n = 7, mean plus or minus S.E,). The force-velocity relation of the portal vein in comparison with other kinds of muscle is discussed.
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| 8. |
- Johansson, B, et al.
(författare)
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Isometric and isotonic relaxation in venous smooth muscle
- 1975
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772. ; 93:2, s. 167-174
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Tidskriftsartikel (refereegranskat)abstract
- The time course of relaxation under isometric and isotonic conditions was studied in preparations of rat portal vein which maintained regular phasic contractions in solutions with increased [K-+] and [Ca-2+]. It was found that the smooth muscle during isotonic lengthening was able to carry the afterload for a period of time which was longer than expected from the control isometric response. The difference was largest for afterloads corresponding to about half the isometric peak force. The terminal decline in force was identical in afterloaded and purely isometric responses. Inhibitory influences of isotonic shortening causing increased rates of relaxation, as reported for striated muscles, were not observed. The differences in the course of relaxation between isotonic and isometric responses of portal vein could not be attributed to variations in membrane excitation. It also appears that the differences are not due to changes in release or uptake of activator calcium, or to presence of viscous elements in the tissue. It is suggested that the ability of the smooth muscle to carry load over a relatively long period during isotonic relaxation may be attributed to the characteristics of the instantaneous force-velocity relations in the force range above Po.
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