Activation of locomotor and grasping spine muscle fibres in chaetognaths: a curious paradox.

Abstract

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 approximately-25 mV and a peak inward current at approximately + 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.

• Authors: I Tsutsui, I Inoue, Q Bone, C Carré
• Journal: Journal of muscle research and cell motility (J Muscle Res Cell Motil) Vol. 21 Issue 1 Pg. 91-7 (Jan 2000) ISSN: 0142-4319 [Print] Netherlands
• PMID: 10813638 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Calcium Channel Blockers
• Central Nervous System Stimulants
• Ions
• Ryanodine
• Caffeine
• Sodium
• Calcium

Topics

• Action Potentials (drug effects, physiology)
• Animals
• Caffeine (pharmacology)
• Calcium (metabolism)
• Calcium Channel Blockers (pharmacology)
• Central Nervous System Stimulants
• Hand Strength (physiology)
• Invertebrates (drug effects, metabolism, ultrastructure)
• Ions
• Motor Activity (drug effects, physiology)
• Muscle Contraction (drug effects, physiology)
• Muscle Fibers, Skeletal (drug effects, metabolism, ultrastructure)
• Muscle, Skeletal (drug effects, metabolism, ultrastructure)
• Patch-Clamp Techniques
• Plankton (drug effects, metabolism, ultrastructure)
• Ryanodine (pharmacology)
• Sodium (metabolism)