title: Isometric contractile properties and velocity of shortening during avian myogenesis.
abstract: Isometric twitch and tetanic contractile properties and velocity of unloaded shortening (V0) of whole avian posterior latissimus dorsi muscle (PLD) were examined between embryonic day 15 and the first 2 wk after hatching. The time to peak twitch force, time to half-relaxation of the twitch response, and time to half-peak tetanic force all change significantly during the final week in ovo but do not change during the first 2 wk ex ovo. Comparisons with previously published reports by others indicate that the twitch half-relaxation time at hatching is approximately the same as that of the adult PLD. The velocity of unloaded shortening increases 2.3-fold during the period studied. It has previously been shown by other that the velocity of shortening is well correlated with a muscle's myosin ATPase activity. Therefore, the observed changes in V0 suggest that the myosin ATPase activity of the avian PLD increases between embryonic day 15 and the first 2 wk posthatching, and this change could account, at least in part, for some of the changes in the isometric properties that were measured.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002642:Chick Embryo; D002645:Chickens; D009119:Muscle Contraction; D009126:Muscle Relaxation; D009132:Muscles / Q000196:embryology*; D009218:Myosins / Q000378:metabolism; D013997:Time Factors
chemical_list: D000251:Adenosine Triphosphatases; D009218:Myosins