Mechanical characteristics of skinned and intact muscle fibres from the giant barnacle,Balanus nubilus |
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Authors: | P J Griffiths J J Duchateau Y Maeda J D Potter C C Ashley |
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Institution: | (1) University Laboratory of Physiology, Parks Road, OXI 3PT Oxford, UK;(2) Laboratoire de Biologie Generale, Universite libre de Bruxelles, 28 Avenue Heger, 1050 Brussels, Belgium;(3) EMBL Outstation, DESY, Notkestrasse 85, 2000 Hamburg 52, Federal Republic of Germany;(4) Department of Pharmacology, University of Miami, 33105 Miami, FL, USA |
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Abstract: | Intact muscle fibres fromBalanus nubilus develop tensions of up to 600 kN sd m−2 during electrical stimulation. The rise of tension occurs with a half-time (177 ms at 12° C) about fivefold longer than that
of tetanised frog muscle at the same temperature. The response of myofibrillar bundles to a rapid stretch resembles that of
frog muscle but has a yo value (i.e. the size of an instantaneous release necessary to just discharge tension) which is ca. 2.5 times smaller, and
phase 2 of the tension transient (the “quick phase”) occurs at a rate comparable to that of frog muscle. In contrast, the
ATPase activity (0.018 mmoles · kg wet weight−1 · s−1) of this preparation and its maximum shortening velocity (0.15–0.16 muscle lengths · s−1) are both at least fivefold slower than frog muscle. These findings can be accounted for by a cross-bridge cycle in barnacle
muscle in which events prior and subsequent to the tension generating step(s) occur at a rate at least fivefold slower than
comparable steps in frog muscle, but the step(s) associated with tension development occur at similar rates in the two preparations.
Since the rate of mechanical relaxation in barnacle muscle is modified in the presence of intracellular calcium buffers and
by depolarisation-induced elevation of the free calcium during the relaxation phase, it is proposed that the time course of
relaxation is not determined exclusively by the kinetics of the cross-bridge cycle, but is also dependent on the free calcium
concentration during relaxation. |
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Keywords: | Barnacle Calcium Mechanics Aequorin |
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