Direct evidence that stomatogastric (Panulirus interruptus) muscle passive responses are not due to background actomyosin cross-bridges |
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Authors: | Jeffrey B Thuma Scott L Hooper |
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Institution: | (1) Neuroscience Program, Department of Biological Sciences, Irvine Hall, Ohio University, Athens, OH 45701, USA |
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Abstract: | Muscles respond to imposed length changes with rapid, large force changes followed by slow relaxations to new steady-state
forces. These responses were originally believed to arise from background levels of actomyosin binding. Discovery of giant
sarcomere-spanning proteins suggested muscle passive responses could arise from length changes of elastic domains present
in these proteins. However, direct evidence that actomyosin plays little role in passive muscle force responses to imposed
length changes has not been provided. We show here that a poison of actomyosin interaction, thiourea, does not alter initial
force changes or subsequent relaxations of lobster stomatogastric muscles. These data provide direct evidence that background
actomyosin cross-bridge formation likely plays, at most, a small role in muscle passive responses to length changes. Thiourea
does not alter lobster muscle electrical responses to motor nerve stimulation, although in this species it does cause tonic
motor nerve firing. This firing limits the utility of thiourea to study lobster muscle electrical responses to motor nerve
stimulation. However, it is unclear whether thiourea induces such motor nerve firing in other animals. Thiourea may therefore
provide a convenient technique to measure muscle electrical responses to motor nerve input without the confounding difficulties
caused by muscle contraction. |
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