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Contractile effects of polycations in permeabilized smooth muscle
K Swärd1, K Dreja, P Hellstrand
1Department of Physiology and Neuroscience, Lund University, Sweden.
Journal of Muscle Research and Cell Motility
|July 31, 1998
Summary
Polycations like spermine enhance muscle force by increasing myosin light chain (LC20) phosphorylation, primarily by inhibiting myosin phosphatase. Additional mechanisms may also contribute to this effect.
Area of Science:
- Muscle physiology
- Biochemistry
Background:
- Smooth muscle contraction is regulated by calcium (Ca2+) and myosin light chain (LC20) phosphorylation.
- Polycations are known to interact with cellular components, but their specific effects on smooth muscle force generation are not fully understood.
Purpose of the Study:
- To investigate the mechanisms by which polycations (spermine, neomycin, polylysine) modulate Ca2+-activated force in guinea-pig ileum smooth muscle.
- To determine the role of myosin light chain phosphorylation and potential alternative pathways in polycation-induced force potentiation.
Main Methods:
- Utilized beta-escin and chi-toxin permeabilized guinea-pig ileum strips to study cellular responses.
- Assessed the effects of various polycations, calmodulin antagonists, and nucleotide replacements (ATP/CTP) on muscle force.
- Measured myosin regulatory light chain (LC20) phosphorylation levels and investigated effects under varying Ca2+, MgATP, and phosphatase inhibition conditions.
Main Results:
- Polycations potentiated Ca2+-activated force, an effect dependent on cellular penetration and inhibited by calmodulin antagonists.
- Potentiation was linked to increased LC20 phosphorylation, suggesting myosin phosphatase inhibition.
- Contractile effects were also observed in Ca2+-free conditions and at low ATP concentrations, indicating phosphorylation-independent mechanisms.
Conclusions:
- Polycations enhance Ca2+-activated force in smooth muscle primarily by inhibiting myosin phosphatase, leading to increased LC20 phosphorylation.
- Additional activation pathways, potentially involving direct myosin activation, contribute to the polycationic effects, especially under low Ca2+ or ATP conditions.