title: Myofibrillar determinants of rate of relaxation in skinned skeletal muscle fibers.
abstract: The influence of Ca2+ dissociation rate from TnC and decreased cross-bridge detachment rate on the time course of relaxation induced by flash photolysis of diazo-2 in rabbit skinned psoas fibers was investigated at 15 degrees C. A TnC mutant (M82Q TnC) that exhibited increased Ca2+ sensitivity caused by a decreased Ca2+ dissociation rate in solution also increased the Ca2+ sensitivity of force and decreased the rate of relaxation in fibers approximately 2-fold. In contrast, a TnC mutant (NHdel TnC) with decreased Ca2+ sensitivity caused by an increased Ca2+ dissociation rate in solution decreased Ca2+ sensitivity of force but did not accelerate relaxation. Decreasing the rate of cross-bridge kinetics by reducing [Pi] slowed relaxation -2-fold and led to two phases of relaxation, a linear phase followed by an exponential phase. In fibers, M82Q TnC further slowed relaxation in low [Pi] approximately 2-fold whereas NHdel TnC had no significant effect on relaxation. These results are consistent with the interpretation that the Ca2+ dissociation rate and cross-bridge detachment rate are similar in fast twitch skeletal muscle such that decreasing either rate slows relaxation but accelerating Ca2+ dissociation has little effect on relaxation.
authors.affiliation: Department of Physiology and Cell Biology, Ohio State University, Columbus, OH 43210, USA.
authors.forename: Ye
authors.initials: Y
authors.lastname: Luo
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Davis
authors.forename: Svetlana B
authors.initials: SB
authors.lastname: Tikunova
authors.forename: Lawrence B
authors.initials: LB
authors.lastname: Smillie
authors.forename: Jack A
authors.initials: JA
authors.lastname: Rall
mesh_terms: D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D003979:Diazonium Compounds; D007537:Isometric Contraction; D007700:Kinetics; D008027:Light; D018485:Muscle Fibers, Skeletal / Q000473:pathology*; D009126:Muscle Relaxation; D018482:Muscle, Skeletal / Q000473:pathology*; D009154:Mutation; D009210:Myofibrils / Q000737:chemistry / Q000502:physiology*; D010642:Phenoxyacetates; D016658:Psoas Muscles / Q000473:pathology; D011817:Rabbits; D011994:Recombinant Proteins / Q000737:chemistry; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013696:Temperature; D013997:Time Factors; D019209:Troponin C / Q000737:chemistry
chemical_list: D002614:Chelating Agents; D003979:Diazonium Compounds; D010642:Phenoxyacetates; D011994:Recombinant Proteins; D019209:Troponin C; C063685:diazo-2; D002118:Calcium