Structure and contractile properties of the ostial muscle (musculus orbicularis ostii) in the heart of the American lobster
Date
1999-08-10
Journal Title
Journal ISSN
Volume Title
Publisher
Springer-Verlag
Abstract
"Venous" blood enters the crustacean heart
through bivalved ostia. Each ostium is a discrete ana-
tomical unit that remains functional even when isolated
from the heart. Muscle ®bers produce overshooting ac-
tion 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 ®bers resembles that of myocardial
®bers. Interconnected bundles of myo®laments occur in
both the ostial ®bers and the myocardial ®bers. In ostial
and myocardial ®bers, the myo®lament bundles are in-
vested 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 sur-
faces of the muscle ®bers are linked by a modest number
of communicating (gap) junctions.
Description
Keywords
Biology
Citation
T. Yazawa, J. L. Wilkens, H. E. D. J. ter Keurs, M. J. Cavey "Structure and contractile properties of the ostial muscle (musculus orbicularis ostii) in the heart of the American lobster" J Comp Physiol B (1999) 169: 529-537