Catch force links and the low to high force transition of myosin.
Catch is characterized by maintenance of force with very low energy utilization in some invertebrate muscles. Catch is regulated by phosphorylation of the mini-titin, twitchin, and a catch component of force exists at all [Ca2+] except those resulting in maximum force. The mechanism responsible for catch force was characterized by determining how the effects of agents that inhibit the low to high force transition of the myosin cross-bridge (inorganic phosphate, butanedione monoxime, trifluoperazine, and blebbistatin) are modified by twitchin phosphorylation and [Ca2+]. In permeabilized anterior byssus retractor muscles from Mytilus edulis, catch force was identified as being sensitive to twitchin phosphorylation, whereas noncatch force was insensitive. In all cases, inhibition of the low to high force transition caused an increase in catch force. The same relationship exists between catch force and noncatch force whether force is varied by changes in [Ca2+] and/or agents that inhibit cross-bridge force production. This suggests that myosin in the high force state detaches catch force maintaining structures, whereas myosin in the low force state promotes their formation. It is unlikely that the catch structure is the myosin cross-bridge; rather, it appears that myosin interacts with the structure, most likely twitchin, and regulates its attachment and detachment.
Department of Physiology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA. thomas.butler@jefferson.edu
Thomas M
TM
Butler
Susan U
SU
Mooers
Marion J
MJ
Siegman
D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism; D003931:Diacetyl / Q000031:analogs & derivatives / Q000494:pharmacology; D006576:Heterocyclic Compounds, 4 or More Rings / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D009218:Myosins / Q000737:chemistry* / Q000502:physiology*; D049880:Mytilus edulis / Q000737:chemistry / Q000502:physiology; D019188:Organ Preservation Solutions / Q000494:pharmacology; D010710:Phosphates / Q000502:physiology; D046509:Tissue Culture Techniques; D014268:Trifluoperazine / Q000494:pharmacology
D006576:Heterocyclic Compounds, 4 or More Rings; D019188:Organ Preservation Solutions; D010710:Phosphates; C004717:diacetylmonoxime; C472645:blebbistatin; D014268:Trifluoperazine; D000242:Cyclic AMP; D009218:Myosins; D003931:Diacetyl