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First published online September 15, 2004
Journal of Experimental Biology 207, 3757-3763 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01206

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Electrical and mechanical properties and mode of innervation in scorpionfish sound-producing muscle fibres

Takakazu Kobayashi^1,*, Tateo Daimon², Ibuki Shirakawa¹, Shigeru Chaen¹ and Haruo Sugi^1,

¹ Department of Physiology, School of Medicine, Teikyo University, Itabashi-ku, Tokyo 173-8605, Japan
² Department of Anatomy, School of Medicine, Teikyo University, Itabashi-ku, Tokyo 173-8605, Japan

View larger version (8K): [in a new window]   Fig. 1. Measurement of membrane electrical constants. (A) Membrane potential changes recorded at the indicated distances from the point of application of inward current pulses (bottom trace). (B) Typical relationship between the membrane potential change (logarithmic scale) and the distance from the current electrode.

View larger version (8K): [in a new window]   Fig. 2. Superimposed records of action potentials (upper traces) and intracellulary applied outward current pulses (lower traces). Action potentials were recorded close to the insertion point of the current electrode. The horizontal line indicates zero potential level in this and Figs 3 and 5.

View larger version (9K): [in a new window]   Fig. 3. Action potentials (A,B) and twitch tension (C) in response to a single motor nerve stimulation. The distance between the recording electrode and the point at which motor nerve entered into the SBM was 0 mm in A and 1.4 mm in B. In this and Fig. 4, broken vertical lines and arrows in A and B indicate the interval between the onset of stimulating current pulse and the onset of action potential.

View larger version (8K): [in a new window]   Fig. 4. Endplate potentials in response to a single motor nerve stimulation. The distance between the recording electrode and the point at which motor nerve entered into the SBM was 0 mm in A, 5 mm in B, and 10 mm in C.

View larger version (12K): [in a new window]   Fig. 5. Electrical and mechanical responses of the SBM. (A) Superimposed recordings of a single isometric twitch in response to a single motor nerve stimulation and a series of twitches in response to repetitive motor nerve stimulation at 100 Hz. The upper and lower traces show action potentials and twitches, respectively. (B) Steady isometric tension in response to transverse a.c. field stimulation (100 Hz).

View larger version (119K): [in a new window]   Fig. 6. Cross-section of the whole swimbladder muscle (SBM; A) and of the whole motor nerve innervating the SBM (B). The number of muscle fibres in the SBM relative to the number of axons in the motor nerve gives the innervation ratio of 6. Bars, 500 µm (A); 50 µm (B).

View larger version (159K): [in a new window]   Fig. 7. Motor nerve branches in the swimbladder muscle (SBM). Note nerve branches running along the SBM fibres. (A) Golgi silver impregnation of nerve branches running along the SBM fibres. (B) Dense distribution of endplates with cholinesterase activity in the SBM fibre. Bars, 200 µm (A); 100 µm (B).

View larger version (146K): [in a new window]   Fig. 8. Cross-sections showing succinic dehydrogenase activity in the swimbladder muscle (SBM) fibres (A) and in the superficial muscle fibres in the animal body (B). Note the weak succinic dehydrogenase activity in the SBM fibres compared to that in the superficial muscle fibres. Bars, 100 µm.

View larger version (150K): [in a new window]   Fig. 9. Cross-sections showing ATPase activity in the swimbladder muscle (SBM) fibres at pH 10.4 (A) and at pH 4.6 (B). Note that the ATPase activity is high at pH 10.4 and low at pH 4.6. Bars, 200 µm.