Summary
Preliminary isometric responses of the paramyosin smooth body wall muscles of Paragordius varius (Nematomorpha) are reported.
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1.
Brief a.c. or d. c. pulses give typical phasic responses, although the time relations are different (Fig. 1A).
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2.
Longer d.c. (5 sec) (Fig. 1A) as well as ACh (10−6 M) stimulation (Fig. 1B) yield tonic contractions with slow decay of developed tension.
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3.
5-Hydroxytryptamine (5-HT) and piperazine citrate (PIP) both relax tonically contracted muscle, but the pattern of subsequent responses to d.c. or ACh stimulation are different (Fig. 1B).
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4.
Tonic tension as a result of ACh (10−6 M) stimulation is decreased proportionately as the concentration of 5-HT is incrementally increased from 10−14 to 10−7 M (Fig. 1C).
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5.
Repetitive a.c. stimulation does not show summation, while similar d.c. stimulation characteristically yields summation (Fig. 1D).
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6.
The occurrence of paramyosin smooth muscle and its properties serves as a basis for understanding the “tight coiling” phenomenon common to fresh-water nematomorphs.
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Swanson, C.J. Isometric responses of the paramyosin smooth muscle of Paragordius varius (Leidy), (Aschelminthes, Nematomorpha). Z. vergl. Physiologie 74, 403–410 (1971). https://doi.org/10.1007/BF00341404
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DOI: https://doi.org/10.1007/BF00341404