| 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. |
- 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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