Structure and contractile properties of the ostial muscle (musculus orbicularis ostii) in the heart of the American lobster |
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Authors: | T Yazawa J L Wilkens M J Cavey H E D J ter Keurs M J Cavey |
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Institution: | (1) Laboratory of Neurobiology, Department of Biology, Tokyo Metropolitan University, Minami-Ohsawa, Hachioji 192-03, Japan, JP;(2) Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4 e-mail: wilkens@ucalgary.ca Tel.: +1-403-2206793; Fax: +1-403-2899311, CA;(3) Department of Medicine and Department of Physiology and Biophysics, Faculty of Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1, CA;(4) Department of Cell Biology and Anatomy, Faculty of Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1, CA |
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Abstract: | “Venous” blood enters the crustacean heart through bivalved ostia. Each ostium is a discrete anatomical unit that remains
functional even when isolated from the heart. Muscle fibers produce overshooting action potentials that have a plateau of
variable duration in response to nervous drive from the cardiac ganglion or during trains of electrical stimuli. Contractions
show summation and facilitation when stimulated by trains of stimuli delivered at rates greater than 0.5 s−1 and 0.2 s−1, respectively. Contraction amplitude increases with stimulating impulse frequency and train duration. Maximum force occurs
at 1.2 times the slack length. The morphology of ostial fibers resembles that of myocardial fibers. Interconnected bundles
of myofilaments occur in both the ostial fibers and the myocardial fibers. In ostial and myocardial fibers, the myofilament
bundles are invested by perforated sheets of sarcoplasmic reticulum, and these sheets interface with a network of sarcolemmal
tubules to form dyadic interior couplings at the level of the sarcomeric H-bands. The contractile apparatus originates and
terminates at intermediate junctions on the transverse cellular boundaries, and the lateral surfaces of the muscle fibers
are linked by a modest number of communicating (gap) junctions.
Accepted: 10 August 1999 |
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Keywords: | Contraction Heart Ostium Homarus americanus (Crustacea) |
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