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Excitation—contraction coupling in skeletal and caudal heart muscle of the hagfish Eptatretus burgeri Girard

Isao Inoue^1,2,*, Izuo Tsutsui^1,3 and Quentin Bone^1,4

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

View larger version (12K): [in a new window]   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+.

View larger version (16K): [in a new window]   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.

View larger version (9K): [in a new window]   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).

View larger version (12K): [in a new window]   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.

View larger version (19K): [in a new window]   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.