title: Drug effect unveils inter-head cooperativity and strain-dependent ADP release in fast skeletal actomyosin.
abstract: Amrinone is a bipyridine compound with characteristic effects on the force-velocity relationship of fast skeletal muscle, including a reduction in the maximum shortening velocity and increased maximum isometric force. Here we performed experiments to elucidate the molecular mechanisms for these effects, with the additional aim to gain insight into the molecular mechanisms underlying the force-velocity relationship. In vitro motility assays established that amrinone reduces the sliding velocity of heavy meromyosin-propelled actin filaments by 30% at different ionic strengths of the assay solution. Stopped-flow studies of myofibrils, heavy meromyosin and myosin subfragment 1, showed that the effects on sliding speed were not because of a reduced rate of ATP-induced actomyosin dissociation because the rate of this process was increased by amrinone. Moreover, optical tweezers studies could not detect any amrinone-induced changes in the working stroke length. In contrast, the ADP affinity of acto-heavy meromyosin was increased about 2-fold by 1 mm amrinone. Similar effects were not observed for acto-subfragment 1. Together with the other findings, this suggests that the amrinone-induced reduction in sliding velocity is attributed to inhibition of a strain-dependent ADP release step. Modeling results show that such an effect may account for the amrinone-induced changes of the force-velocity relationship. The data emphasize the importance of the rate of a strain-dependent ADP release step in influencing the maximum sliding velocity in fast skeletal muscle. The data also lead us to discuss the possible importance of cooperative interactions between the two myosin heads in muscle contraction.
authors.affiliation: School of Pure Applied Natural Science, University of Kalmar, SE-391 82 Kalmar, Sweden.
authors.forename: Nuria
authors.initials: N
authors.lastname: Albet-Torres
authors.forename: Marieke J
authors.initials: MJ
authors.lastname: Bloemink
authors.forename: Tom
authors.initials: T
authors.lastname: Barman
authors.forename: Robin
authors.initials: R
authors.lastname: Candau
authors.forename: Kerstin
authors.initials: K
authors.lastname: Frölander
authors.forename: Michael A
authors.initials: MA
authors.lastname: Geeves
authors.forename: Kerstin
authors.initials: K
authors.lastname: Golker
authors.forename: Christian
authors.initials: C
authors.lastname: Herrmann
authors.forename: Corinne
authors.initials: C
authors.lastname: Lionne
authors.forename: Claudia
authors.initials: C
authors.lastname: Piperio
authors.forename: Stephan
authors.initials: S
authors.lastname: Schmitz
authors.forename: Claudia
authors.initials: C
authors.lastname: Veigel
authors.forename: Alf
authors.initials: A
authors.lastname: Månsson
mesh_terms: D000205:Actomyosin / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000378:metabolism*; D000676:Amrinone / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D002121:Calcium Channel Blockers / Q000737:chemistry / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D008954:Models, Biological; D015394:Molecular Structure; D009119:Muscle Contraction / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D009210:Myofibrils / Q000187:drug effects / Q000378:metabolism; D015879:Myosin Subfragments / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D011817:Rabbits
chemical_list: D002121:Calcium Channel Blockers; D015879:Myosin Subfragments; D000244:Adenosine Diphosphate; D000205:Actomyosin; D000676:Amrinone