Regulation of catch muscle by twitchin phosphorylation: effects on force, ATPase, and shortening.
Recent experiments on permeabilized anterior byssus retractor muscle (ABRM) of Mytilus edulis have shown that phosphorylation of twitchin releases catch force at pCa > 8 and decreases force at suprabasal but submaximum [Ca2+]. Twitchin phosphorylation decreases force with no detectable change in ATPase activity, and thus increases the energy cost of force maintenance at subsaturating [Ca2+]. Similarly, twitchin phosphorylation causes no change in unloaded shortening velocity (Vo) at any [Ca2+], but when compared at equal submaximum forces, there is a higher Vo when twitchin is phosphorylated. During calcium activation, the force-maintaining structure controlled by twitchin phosphorylation adjusts to a 30% Lo release to maintain force at the shorter length. The data suggest that during both catch and calcium-mediated submaximum contractions, twitchin phosphorylation removes a structure that maintains force with a very low ATPase, but which can slowly cycle during submaximum calcium activation. A quantitative cross-bridge model of catch is presented that is based on modifications of the Hai and Murphy (1988. Am. J. Physiol. 254:C99-C106) latch bridge model for regulation of mammalian smooth muscle.
Butler
T M
TM
Department of Physiology, Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA. butlert@jeflin.tju.edu
Mooers
S U
SU
Li
C
C
Narayan
S
S
Siegman
M J
MJ
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D049872:Bivalvia; D029742:Caenorhabditis elegans Proteins; D002118:Calcium / Q000378:metabolism; D002148:Calmodulin-Binding Proteins / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008956:Models, Chemical; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009124:Muscle Proteins / Q000378:metabolism*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D010766:Phosphorylation; D012623:Seawater; D013314:Stress, Mechanical
D029742:Caenorhabditis elegans Proteins; D002148:Calmodulin-Binding Proteins; D009124:Muscle Proteins; C489233:unc-22 protein, C elegans; C022571:adenosine 5'-O-(3-thiotriphosphate); D004533:Egtazic Acid; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D000251:Adenosine Triphosphatases; D002118:Calcium