Giant smooth muscle cells of Beroë. Ultrastructure, innervation, and electrical properties.

Abstract

Beroë muscle fibers are single cells which may be 20-40 micrometer in diameter in mature specimens. Longitudinal muscles may be 6 cm or more long. There is no striation pattern and the muscles were observed to contract in a tonic fashion when stretched. They are innervated by a nerve net, and external recording revealed what are probably nerve net impulses. Intracellular stimulation of the muscles themselves was found to initiate large propagating action potentials which were recorded intracellularly. The action potentials were insensitive to tetrodotoxin (10(-5) g/ml), tetraethylammonium ions (50 mM), MnCl2 (25 mM), and low concentrations of verapamil (2 X 10(-6) g/ml). Full-size action potentials were recorded in sodium- or calcium-deficient salines, but were small and graded in salines deficient in both sodium and calcium. Cable analysis yielded mean values for lambda (1.95 mm), Ri (154 omega cm), Rm (9,253 omega cm2), and tau m (13.9 ms). The conduction velocity depended primarily on fiber diameter and maximum rate of rise of the action potential and could be predicted from the theoretical analysis of Hunter et al. (1975 Prog. Biophys. Mol. Biol. 30: 99-144). The calculated membrane capacity (less than microF/cm2) indicates little infolding of the surface membrane, a conclusion which is in agreement with anatomical studies.

Physiology and Evolution of Voltage-Gated Calcium Channels in Early Diverging Animal Phyla: Cnidaria, Placozoa, Porifera and Ctenophora

“…One notable distinction was their kinetics, with one channel bearing fast inactivation producing fast, transient Ca 2+ currents, and the other much slower inactivation, producing slow, long-lasting currents (Dubas et al, 1988). Similar depolarizing Ca 2+ /Na + currents were reported for the action potential of giant muscle cells isolated from B. ovata (Hernandez-Nicaise et al, 1980, 1982; Bilbaut et al, 1988a,b). For both species, Ca 2+ influx through the channels seems required for contraction, since removal of external Ca 2+ or pharmacological disruption abrogates muscle action potentials and contractions (Hernandez-Nicaise et al, 1980; Anderson, 1984; Bilbaut et al, 1988a,b; Dubas et al, 1988; Cario et al, 1996).…”

“…Similar depolarizing Ca 2+ /Na + currents were reported for the action potential of giant muscle cells isolated from B. ovata (Hernandez-Nicaise et al, 1980, 1982; Bilbaut et al, 1988a,b). For both species, Ca 2+ influx through the channels seems required for contraction, since removal of external Ca 2+ or pharmacological disruption abrogates muscle action potentials and contractions (Hernandez-Nicaise et al, 1980; Anderson, 1984; Bilbaut et al, 1988a,b; Dubas et al, 1988; Cario et al, 1996). Unfortunately, while the available data provides convincing evidence for the existence of distinct voltage-gated Ca 2+ channels present in ctenophore smooth muscle, little can be said about the specific channel types at play.…”

Elements of a ‘nervous system’ in sponges

“…But how related are the elements of these systems? Neuroid or non-nervous conduction in giant plant or algal cells such as Mimosa or Nitella (Fromm and Lautner, 2007) functions similarly to the neuroid conducting tissues of glass sponge syncytia, and to the gap junction-coupled epithelia of cnidarians, ctenophores and other animals (Mackie, 1965;Bassot et al, 1978;Hernandez-Nicaise et al, 1980;Leys and Mackie, 1997). Different ions form the basis of the action potentials (chloride and calcium potentials in the plant and alga, calcium in the sponge, and sodium or calcium in cnidarians and ctenophores) but the effect is similargenerating a rapid signal that effects a behavioural response.…”

Functional morphology of the tentacles and tentilla of Coeloplana bannworthi (Ctenophora, Platyctenida), an ectosymbiont of Diadema setosum (Echinodermata, Echinoida)

“…Its structure, a central axis including several nuclei with organelles and a peripheral muff of myofilaments, suggests that it is close to the giant smooth muscle cell described in the mesoglea of Beroe species (see Hernandez-Nicaise and Nicaise 1985; HernandezNicaise 1991 for a detailed description of these cells). In these Ctenophora, the myofilaments would be organized in contractile myofibril-like units (Hernandez-Nicaise and Nicaise 1985;Hernandez-Nicaise 1991). Similarly, transverse sections through the giant muscle cells in C. bannworthi have shown well-separated sets of myofilaments that could be homologous to the contractile myofibril-like units.…”