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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Abbreviations
- PEVK:
-
Amino acid sequence: proline-glutamic acid-valine-lysine
- EJP:
-
Excitatory junction potential
- BTS:
-
N-benzyl-p-toluenesulfonamide
- lvn:
-
Lateral ventricular nerve
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Acknowledgments
We thank RA DiCaprio for comments on the manuscript. The experiments comply with the “Principles of animal care”, publication No. 86-23, revised 1985 of the National Institute of Health and also with the current laws of the United States. This project was funded by National Science Foundation award #IOS-0958926 and the National Institute on Drug Abuse grant #1RC1DA028494-01 to SLH and the Ohio University Baker Fund and Neuroscience Program.
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Thuma, J.B., Hooper, S.L. Direct evidence that stomatogastric (Panulirus interruptus) muscle passive responses are not due to background actomyosin cross-bridges. J Comp Physiol A 196, 649–657 (2010). https://doi.org/10.1007/s00359-010-0553-1
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DOI: https://doi.org/10.1007/s00359-010-0553-1