Polyamines inhibit myosin phosphatase and increase LC20 phosphorylation and force in smooth muscle.
The increase in Ca(2+)-activated force caused by polyamines in beta-escin-permeabilized guinda pig ileum is shown to be associated with increased myosin 20-kDa light chain (LC20) phosphorylation and shortening velocity. Myosin LC20 dephosphorylation with arrested kinase activity was slower in the presence of 1 mM spermine. Smooth muscle phosphatases (SMP-I, -II, -III, and -IV) isolated from turkey gizzard are all active against phosphorylated LC20, but only SMP-III and -IV dephosphorylate heavy meromyosin (HMM). Spermine inhibited SMP-III activity toward LC20 but stimulated HMM dephosphorylation, whereas SMP-IV was inhibited with both substrates. In contrast, SMP-I and -II were stimulated by spermine. The relative effects of different polyamines correlated with an increasing number of positive charges. Spermine did not affect binding of SMP-IV to myosin and did not dissociate any of the subunits of the enzyme. Incubation of permeabilized strips with SMP-IV resulted in attenuated responses to Ca2+, an effect that was opposed by spermine and abolished by microcystin-LR. We conclude that spermine selectively inhibits myosin phosphatase activity and suggest that polyamines function as endogenous myosin phosphatase inhibitors.
Swärd
K
K
Department of Physiology and Biophysics, University of Lund, Sweden.
Pato
M D
MD
Nilsson
B O
BO
Nordström
I
I
Hellstrand
P
P
D000818:Animals; D005260:Female; D005895:Gizzard, Avian / Q000378:metabolism; D006168:Guinea Pigs; D007082:Ileum / Q000378:metabolism; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000201:enzymology* / Q000502:physiology*; D018994:Myosin Light Chains / Q000378:metabolism*; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism; D043263:Myosin-Light-Chain Phosphatase; D010539:Permeability; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D010744:Phosphoric Monoester Hydrolases / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011073:Polyamines / Q000494:pharmacology*; D013096:Spermine / Q000494:pharmacology; D014422:Turkeys / Q000378:metabolism
D018994:Myosin Light Chains; D011073:Polyamines; D013096:Spermine; D009219:Myosin-Light-Chain Kinase; D010749:Phosphoprotein Phosphatases; D010744:Phosphoric Monoester Hydrolases; D043263:Myosin-Light-Chain Phosphatase