Excitation—contraction coupling in skeletal and caudal heart muscle of the hagfish Eptatretus burgeri Girard
Isao Inoue1,2,*,
Izuo Tsutsui1,3 and
Quentin Bone1,4
1 The Ine Marine Laboratory of National Institute for Physiological
Sciences, Ine, Kyoto 626-0424, Japan
2 Institute for Enzyme Research, Tokushima University, Tokushima 770-8503,
Japan
3 Laboratory of Biology, Graduate School of Commerce and Management,
Hitotsubashi University, Kunitachi, Tokyo 186-8601, Japan
4 Marine Biological Association of UK, Plymouth PL1 2PB, UK
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Fig. 1. (A) Propagating action potential recorded from a white muscle fibre of
musculus tubulatus using a microelectrode. The dotted line indicates
0 mV. External solution, artificial seawater (ASW). (B) Force generated by a
bundle of seven white muscle fibres in response to electrical stimulation
measured with a strain gauge. Ten traces were averaged. Arrows indicate when
stimulation was applied with a suction electrode. (Bi) Recorded in ASW, (Bii)
recorded 10 min after the external ASW was switched to 0Ca2+-ASW
containing 10 mmol l-1 Co2+.
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Fig. 5. (A) An increase in the fluorescence intensity ( F/F)
indicating an increase in the intracellular Ca2+ concentration of a
single caudal heart muscle fibre associated with depolarisation produced by an
increase in the external K+ concentration to 100 mmol
l-1 at the time marked by arrow. The fibres had been loaded with
fluo-3 by immersing in 0Ca2+-ASW containing 30 mmol l-1
Co2+ and 2 µmol l-1 fluo-3-AM for 1.5 h. The bath
solution was 0Ca2+-ASW containing 30 mmol l-1
Co2+. The dotted line indicates the background fluorescence
measured off the cell. (B) Effect of changing the external K+
concentration on the membrane potential of caudal heart muscle fibres. Values
are means ± S.D. obtained from 10 fibres. The slope was obtained by
linear regression to the mean values, and is 35.2 mV per tenfold change in the
K+ concentration.
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Fig. 2. Force generation measured with a strain gauge in response to depolarisation
produced by an elevation of external K+ concentration to 100 mmol
l-1 in red skeletal muscle fibres. The red muscle fibre tissue was
pre-soaked in 0Ca2+-ASW containing 10 mmol l-1
Co2+ for 1.5 h. 0.6 mol l-1 KCl solution was added to
the bath at the time indicated (+KCl), and the external solution was switched
back to the original 0Ca2+-ASW containing 10 mmol l-1
Co2+ at time (-KCl).
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Fig. 3. (A) Subthreshold response and all-or-none spike recorded from a caudal
heart muscle fibre in response to electrical stimulation by a suction
electrode. Two traces are superimposed. External solution, artificial seawater
(ASW). The dotted line indicates 0 mV. (Bi-iii) Reversible suppression by
externally applied d-tubocurarine (d-TC; 20  mol l-1) of
subthreshold responses evoked by a train of electrical stimuli by a suction
electrode. The dotted lines indicate 0 mV. The recordings in A and in B were
obtained from different individual caudal heart muscle fibres.
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Fig. 4. Effects of 0Ca2+-ASW containing 10 mmol l-1
Co2+ and of 0Na+-ASW on twitches of a single caudal
heart muscle fibre electrically stimulated every 2 s with a microelectrode
inserted into the fibre. Twitches were detected with a CdS photocell from a
video monitor screen. ASW, artificial seawater.
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© The Company of Biologists Ltd 2002
