Contractile effects of polycations in permeabilized smooth muscle.
The polycations spermine, neomycin and polylysine potentiated Ca(2+)-activated force in beta-escin permeabilized guinea-pig ileum strips. The effect was inhibited by the calmodulin antagonists trifluoperazine, mastoparan and W13. Potentiation was slow or absent in chi-toxin permeabilized strips, indicating dependence on penetration of the polycations into cells. The effects of spermine and neomycin were maintained after extensive permeabilization by beta-escin, which eliminated the contractile effect of GTPgammaS. Replacement of ATP by CTP, which is not a substrate for myosin light chain kinase, inhibited contractile potentiation. Potentiation of Ca(2+)-activated contractions was associated with increased phosphorylation of the myosin regulatory light chains (LC20). A contractile effect of polylysine and neomycin was also seen in Ca(2+)-free medium and after partial LC20 thiophosphorylation, indicating that phosphorylation-independent processes may contribute to the response. Although spermine does not cause contraction in Ca(2+)-free medium at physiological [MgATP], it did so when [MgATP] was lowered to 40 micron. Similar to high-[Mg2+], the rate of contraction on addition of ATP to strips incubated with microcystin-LR in inhibit phosphatase activity was increased by the polycations, but only at [Ca2+] < 0.3 micron. The results suggest that polycations increase Ca(2+)-activated force by inhibiting myosin phosphatase activity, thereby increasing myosin LC20 phosphorylation. However, additional activation mechanisms, evident at low [Ca2+] and at low [ATP] and possibly involving direct activation of myosin, contribute to their effect.
Swärd
K
K
Department of Physiology and Neuroscience, Lund University, Sweden.
Dreja
K
K
Hellstrand
P
P
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002412:Cations / Q000494:pharmacology*; D003570:Cytidine Triphosphate / Q000378:metabolism; D004928:Escin; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000502:physiology; D036341:Intercellular Signaling Peptides and Proteins; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D018994:Myosin Light Chains / Q000378:metabolism; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism; D009355:Neomycin / Q000494:pharmacology; D010455:Peptides; D010766:Phosphorylation; D011073:Polyamines / Q000494:pharmacology*; D000071228:Polyelectrolytes; D011107:Polylysine / Q000494:pharmacology; D013096:Spermine / Q000494:pharmacology; D013449:Sulfonamides / Q000494:pharmacology; D013997:Time Factors; D014268:Trifluoperazine / Q000494:pharmacology; D010738:Type C Phospholipases; D014862:Wasp Venoms / Q000494:pharmacology
D000255:Adenosine Triphosphate; D002118:Calcium; D002147:Calmodulin; D002412:Cations; D003570:Cytidine Triphosphate; D004928:Escin; D036341:Intercellular Signaling Peptides and Proteins; D018994:Myosin Light Chains; D009219:Myosin-Light-Chain Kinase; D009355:Neomycin; D010455:Peptides; D011073:Polyamines; D000071228:Polyelectrolytes; D011107:Polylysine; D013096:Spermine; D013449:Sulfonamides; D014268:Trifluoperazine; D010738:Type C Phospholipases; D014862:Wasp Venoms; C037500:mastoparan; C033772:N-(4-aminobutyl)-5-chloro-2-naphthalenesulfonamide