Ca(2+)-insensitive sustained contraction of skinned smooth muscle after acidic ADP treatment.
After an acidic treatment in the presence of ADP, Triton X-100-skinned rabbit aortic smooth muscle strips were found to develop a large sustained, Ca(2+)-insensitive tension when returned to a relaxing solution with neutral pH. The presence of ADP during treatment was essential for the manifestation of the Ca(2+)-insensitive contraction. This contraction was reversibly eliminated by withdrawal of MgATP or addition of vanadate and was found to be accompanied by an extraordinarily high level of 20-kDa myosin light-chain (MLC20) phosphorylation. The rate constant for dephosphorylation of MLC20 in treated strips was about one-twenty-fifth that in untreated control, when determined after removal of Ca2+, Mg2+, and ATP. Two-dimensional phosphopeptide mapping of tryptic digests of MLC20 showed that most incorporated phosphate was in the peptides which would be phosphorylated by myosin light-chain kinase. These results provide strong evidence that ADP inactivates myosin light-chain phosphatase under acidic conditions.
Department of Pharmacology, Juntendo University School of Medicine, Tokyo, Japan.
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Morimoto
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Ogawa
D000143:Acids / Q000494:pharmacology*; D000244:Adenosine Diphosphate / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004351:Drug Resistance; D006652:Histological Techniques; D006863:Hydrogen-Ion Concentration; D007537:Isometric Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism; D009218:Myosins / Q000378:metabolism; D010766:Phosphorylation; D011817:Rabbits; D014661:Vasoconstriction / Q000187:drug effects*
D000143:Acids; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D009219:Myosin-Light-Chain Kinase; D009218:Myosins; D002118:Calcium