Possible involvement of actomyosin ADP complex in regulation of Ca2+ sensitivity in alpha-toxin permeabilized smooth muscle.
The effects of substrate condition and ADP beta S on the pCa2+-tension relationships were investigated, using alpha-toxin permeabilized rabbit mesenteric artery at 37 degrees C. The contraction induced by 10 microM Ca2+ solution after permeabilization was as large as that induced by 145 mM K+ PSS solution containing 10 microM NE in the intact tissue, indicating that the majority of the cells were permeabilized. The Ca2+ sensitivity was greatly affected by the substrate condition and increasing the ratio of ATP/CP induced a leftward shift of the pCa2+-tension curve. Addition of 100 microM ADP beta S had a similar effect. When the ATP/CP ratio was high, the 0.1 microM Ca2+ solution relaxed the tissue precontracted by 10 microM Ca2+ solution more slowly showing hysteresis. One mM vanadate, which is reported to relax muscle by forming actomyosin-ADP-Vi (AM-ADP-Vi), completely inhibited both contractions induced by 0.18 microM Ca2+ solution containing 2 mM MgADP and 0.3 microM Ca2+ solution containing 0.3 microM PDBu. These results indicated that the population of AM-ADP complex in the crossbridge had increased due to the accumulation of ADP inside the tissue or activation of PKC and that the inhibition of ADP release from AM-ADP complex may be playing a key role in increasing Ca2+ sensitivity of myofilaments.
Nishimura
J
J
Department of Pharmacology, University of Miami, School of Medicine, Florida 33101.
van Breemen
C
C
D000205:Actomyosin / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000378:metabolism* / Q000494:pharmacology / Q000031:analogs & derivatives; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002463:Cell Membrane Permeability; D003039:Cobra Neurotoxin Proteins / Q000494:pharmacology*; D004546:Elapid Venoms / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D008638:Mesenteric Arteries / Q000187:drug effects / Q000502:physiology*; D008962:Models, Theoretical; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D011485:Protein Binding; D011817:Rabbits; D013873:Thionucleotides / Q000494:pharmacology; D014638:Vanadates / Q000494:pharmacology
D003039:Cobra Neurotoxin Proteins; D004546:Elapid Venoms; D013873:Thionucleotides; C030812:adenosine 5'-O-(2-thiodiphosphate); D014638:Vanadates; D000244:Adenosine Diphosphate; C025154:alpha-cobratoxin; D000205:Actomyosin; D002118:Calcium