| 1. |
- Månsson, Alf, et al.
(författare)
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Effects of amrinone on the contractile behaviour of frog striated muscle fibres
- 1985
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Ingår i: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 125:3, s. 481-493
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Tidskriftsartikel (refereegranskat)abstract
- The effects of amrinone (0.005–2.1 mM) were studied on isolated single muscle fibres of the frog (0.6–4.3 °C). In the concentrations used amrinone potentiated the isometric twitch, increased the initial rate of force development and prolonged the time to peak twitch force and the time from peak force to half relaxation. There was a moderate but statistically significant (P < 0.001) enhancement of the maximum tetanic force and a marked slowing of the relaxation phase of the tetanus. Amrinone depressed the velocity of unloaded shortening by 33 ± 2% (mean ± SE, π= 6) and reduced the curvature of the force-velocity relation leading to an increase of a/PO in Hill's (1938) hyperbolic equation. In accordance with the effects of amrinone on the force–velocity relation, there was a decrease in the rate of redevelopment of force after the fibre was released to zero tension during the tetanus plateau. The evidence suggests that the drug affects the contractile properties of frog muscle fibres by two different mechanisms: (1) amrinone affects the excitation–contraction coupling causing enhanced calcium release in response to membrane excitation and (2) amrinone exerts a direct effect on the kinetics of turnover of the myosin cross-bridges. The latter aspect of the drug effect was evaluated in terms of A. F. Huxley's (1957) cross-bridge model by means of a computer program.
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| 2. |
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| 3. |
- Månsson, Alf, et al.
(författare)
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Effects of amrinone on twitch, tetanus and shortening kinetics in mammalian skeletal muscle
- 1989
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Ingår i: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 136:1, s. 37-45
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Tidskriftsartikel (refereegranskat)abstract
- The contractile effects of amrinone were studied on twitch and tetanus responses of mouse lumbrical muscles. Amrinone (1.1 mM) increased the maximum force level during the tetanus, reduced the rate of rise of force during the onset of tetanus and prolonged the time from the last stimulus to half-relaxation. The rate of redevelopment of force after a release during the tetanus plateau was likewise reduced. Amrinone (I.I 0.5 mM) increased the time to peak twitch force and the time to half-relaxation during the twitch. The peak twitch force was not significantly changed. The force-velocity relation was markedly affected by amrinone: there was a decrease in maximum velocity of shortening, an increase in maximum isometric force and a decrease in curvature of the force–velocity relation. The results suggest that amrinone modulates the kinetic properties of the myosin cross-bridges by exerting a specific effect upon the myofilament system. The latter effects are mainly responsible for the contractile changes produced by amrinone in mouse skeletal muscle. Amrinone appears to have little effect on the metabolism of activator calcium in this particular preparation.
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| 4. |
- Månsson, Alf
(författare)
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The effects of tonicity on tension and stiffness of tetanized skeletal muscle fibres of the frog
- 1989
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Ingår i: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 136:2, s. 205-216
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Tidskriftsartikel (refereegranskat)abstract
- Tension and stiffness of tetanically activated skeletal muscle fibres of the frog were studied at varied tonicity of the extracellular medium (1.7–3.2 °C; sarcomere length, 2.13–2.22 μm). The stiffness was measured from the change in peak tension in response to fast (0.2 ms) stretches and releases of small amplitude (0.11–0.15% of the fibre length). The bathing solution was made hypotonic by reduction of NaCl and hypertonic by addition of sucrose. The osmotic strength of the solutions tested varied from 81 to 168% of the isotonic value. Maximum tetanic tension decreased markedly with increased tonicity. The active stiffness, on the other hand, increased as the tonicity was raised, and the tension/stiffness ratio (the total extension of the undamped fibre elasticity) was thus greatly reduced under these conditions. Evidence is presented to show that the change in the tension/stiffness ratio is due neither to the development of rigor cross-bridges nor to the recruitment of passive parallel-elastic elements in response to increased tonicity. Neither are viscous-like components important for explaining the effect. A change in the tension/stiffness ratio, similar to that seen in response to increased tonicity, did not occur as fibre width was reduced by increasing the sarcomere length. This suggests that the changes in the fibre volume affect this ratio mainly by mechanisms that are unrelated to changes in lateral spacing between the myofilaments.
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| 5. |
- Mörner, J, et al.
(författare)
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Effects of amrinone on the electromechanical coupling in frog skeletal muscle fibres
- 1990
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Ingår i: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 139, s. 289-295
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Tidskriftsartikel (refereegranskat)abstract
- The contractile effects of I.I mM amrinone were studied on isolated skeletal muscle fibres of the frog (2–5 °C, slack length). Amrinone potentiated the twitch amplitude and the maximum tetanic tension and also enhanced the maximum contracture response elicited by 117.5 mM K+ (mean increase 6.3 ± 1.8 %, n = 6, P < 0.02). The time to halfrelaxation of the potassium contracture was slightly increased (mean change 13.8 ± 3.5%, n = 7, P < 0.01). Amrinone furthermore shifted the S-shaped curve relating contracture tension to log K+ to the left, and thus reduced the threshold depolarization (the mechanical threshold needed) to elicit a contracture (mean reduction 11 ± 1 mV). The duration of the action potential at the –25 mV level was slightly increased by amrinone, whereas the resting membrane potential was unaffected.
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