caa a22 4500 475744721 CHVBK 20180406123510.0 cr unu---uuuuu 170329e20000101xx s 000 0 eng 10.1023/A:1005627918789 doi (NATIONALLICENCE)springer-10.1023/A:1005627918789 Activation of locomotor and grasping spine muscle fibres in chaetognaths: a curious paradox [Elektronische Daten] [I. Tsutsui, I. Inoue, Q. Bone, C. Carré] Chaetognath muscle fibres resemble vertebrate muscle fibres in having an abundant sarcoplasmic reticulum (SR) and analogues of the transverse (T) tubular system, but contraction is regulated differently. In intact chaetognaths electrically-evoked contractions of the striated locomotor muscles were largely or totally blocked by d-tubocurarine, by surgical removal of the ventral ganglion and by Co2+. Contractions of single cells enzymatically dissociated from locomotor muscles were likewise blocked by Co2+, they twitched once only after calciseptine, showed neither contractures nor elevated intracellular Ca2+ with caffeine, and ryanodine did not block contractions. Whole cell voltage-clamped locomotor muscle cells displayed a typical inward rectified Ca2+ current that was sensitive to the Ca2+ channel blockers nifedipine and calciseptine and showed voltage-dependent activation with a threshold at ∼−25 mV and a peak inward current at ∼+ 10 mV. In contrast, whole cell voltage-clamped cells from the muscles operating the grasping spines of the head showed an initial very rapid and rapidly-inactivating inward current abolished by tetrodotoxin (TTX), followed by a slower and slowly-inactivating inward current blocked by calciseptine. The relation between these observations and the unusual ‘vertebrate-like' structure of the muscle cells is discussed. Kluwer Academic Publishers, 2000 Tsutsui I. National Institute for Physiological Science, 444-8585, Okazaki, Japan aut Inoue I. Institute for Enzyme Research, Tokushima University, 770-0043, Tokushima, Japan aut Bone Q. Marine Biological Association Laboratory, PL1 2PB, Plymouth, UK aut Carré C. Station Zoologique, 06230, Villefranche-s-Mer, France aut Journal of Muscle Research & Cell Motility Kluwer Academic Publishers 21/1(2000-01-01), 91-97 0142-4319 21:1<91 2000 21 10974 https://doi.org/10.1023/A:1005627918789 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1023/A:1005627918789 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Tsutsui I. National Institute for Physiological Science, 444-8585, Okazaki, Japan aut NATIONALLICENCE 700 1- Inoue I. Institute for Enzyme Research, Tokushima University, 770-0043, Tokushima, Japan aut NATIONALLICENCE 700 1- Bone Q. Marine Biological Association Laboratory, PL1 2PB, Plymouth, UK aut NATIONALLICENCE 700 1- Carré C. Station Zoologique, 06230, Villefranche-s-Mer, France aut NATIONALLICENCE 773 0- Journal of Muscle Research & Cell Motility Kluwer Academic Publishers 21/1(2000-01-01), 91-97 0142-4319 21:1<91 2000 21 10974 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer