Effects of ADP and low ATP on the Ca(2+)-sensitive transient contraction upon photolysis of caged ATP in rat muscle fibres: a study on the Bremel-Weber type cooperation.
Caged ATP was photolysed in rat psoas fibres under various conditions to examine whether ADP plays a special role in the 'Bremel-Weber type cooperation', viz. the Ca(2+)-like action of the rigor cross-bridges. Various concentrations of ATP (0.25-1.6 mM) were photoreleased in the presence of various concentrations of ADP (0-0.4 mM) at approximately 8 or 20 degrees C. The Ca2+ concentration was set at around 0.2 microM in order that the ATP-induced contraction was significant but short. Both lower [ATP] and higher [ADP] resulted in a slower detachment of the rigor cross-bridges and a larger contraction after the detachment. ADP did not seem to affect the relationship between the rate of detachment and the size of the Ca(2+)-sensitive component of the subsequent contraction. It is concluded that there is little evidence that the ADP-bound rigor cross-bridges are more potent than the nucleotide-free ones in the Bremel-Weber type cooperation that is seen in the ATP-induced transient contraction. The mechanism by which the ADP-specific, Ca(2+)-independent contraction occurs immediately after the release of ATP remains to be clarified.
Department of Physiology, Oita Medical University, Japan. khoriuti@oita-med.ac.jp
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D000244:Adenosine Diphosphate / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics*; D003432:Cross-Linking Reagents / Q000378:metabolism; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D010777:Photochemistry; D016658:Psoas Muscles / Q000166:cytology / Q000378:metabolism; D051381:Rats; D013696:Temperature
D003432:Cross-Linking Reagents; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D002118:Calcium