Long-lasting potassium channel inactivation in myoepithelial fibres is related to characteristics of swimming in diphyid siphonophores.

Diphyid siphonophores swim using bursts of propulsive jets, which are produced by contractions of a monolayer of subumbrellar myoepithelial fibres lining the nectophore. This swimming behaviour is characterised by successive increases in the force generating the jets during the initial jets of the burst. Action potentials that generate the contractions propagate throughout the myoepithelial layer: both their amplitude and duration successively increase during the first part of the burst.

GABAergic synaptic transmission modulates swimming in the ascidian larva.

To examine the role of the amino acid GABA in the locomotion of basal chordates, we investigated the pharmacology of swimming and the morphology of GABA-immunopositive neurones in tadpole larvae of the ascidians Ciona intestinalis and Ciona savignyi. We verified that electrical recording from the tail reflects alternating muscle activity during swimming by correlating electrical signals with tail beats using high-speed video recording. GABA reversibly reduced swimming periods to single tail twitches, while picrotoxin increased the frequency and duration of electrical activity associated with spontaneous swimming periods.

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

Hagfishes are regarded as the most primitive living craniates. Excitation-contraction (E-C) coupling mechanisms were studied in skeletal and caudal heart muscle fibres of the hagfish Eptatretus burgeri. In white (fast) skeletal muscle fibres from the musculus tubulatus, force generation in response to electrical stimulation was maintained in nominally Ca(2+) free artificial seawater (ASW) (0Ca(2+)-ASW) containing 10 mmol l(-1) Co(2+) (a blocker of Ca(2+) currents).

Excitation-contraction coupling in isolated locomotor muscle fibres from the pelagic tunicate Doliolum which lack both sarcoplasmic reticulum and transverse tubular system.

In the locomotor muscle of the pelagic tunicate Doliolum, both the sarcoplasmic reticulum (SR) and the transverse-tubular (T-tubular) system are absent. The mechanism of excitation-contraction (E-C) coupling was studied in single muscle fibres enzymatically dissociated from Doliolum denticulatum. Whole cell voltage clamp experiments demonstrated an inward ionic current associated with membrane depolarisation.

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

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 +.