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Q Bone

Publications and source records attributed to Q Bone.

At least 19 recordsLinked to original sources
PubMed1997

Contraction and relaxation in the absence of a sarcoplasmic reticulum: muscle fibres in the small pelagic tunicate Doliolum.

Previous ultrastructural observations suggested that Doliolum muscle fibres apparently lacked both sarcoplasmic reticulum and transverse tubular-system. External Ca2+ is required for contraction, caffeine does not evoke contraction, nor does it increase intracellular Ca2+ level. Ryanodine at 50 microM has no effect on electrically-evoked contractions. Further, electrical stimulation in external solutions lacking Na+ leads to sustained contracture. We conclude that intracellular Ca2+ stores are absent in these rapid obliquely-striated fibres, and that reduction in internal Ca2+ levels following contraction depends upon Na(+)-Ca2+ exchange across the sarcolemma.

Animals↗
PubMed1997

Contractile properties of obliquely striated muscle from the mantle of squid (Alloteuthis subulata) and cuttlefish (Sepia officinalis)

The mechanical properties of obliquely striated muscle fibres were investigated using thin slices of mantle from squid Alloteuthis subulata and cuttlefish Sepia officinalis. Brief tetani or twitch stimuli were used as this pattern is likely to occur during jetting of the intact animal. The length­active force relationship for twitches and tetani (0.1s, 50Hz) was similar to that of vertebrate cross-striated fibres. Passive force at the length giving maximum tetanic force was 0.13±0.05P0 (mean ± s.e.m., N=6, where P0 is maximum isometric tetanus force) and increased steeply at longer lengths. Peak force in a brief isometric tetanus (0.2s, 100­150Hz) was 262±16mNmm-2 cross-sectional area of wet tissue (N=6) for squid, and 226±19mNmm-2 (N=7) for cuttlefish. The force­velocity relationship for isotonic shortening during twitches of squid mantle slices was a 'double hyperbolic' relationship as described for cross-striated fibres by Edman. Fitting Edman's equation to the results gave: P*=1.18±0.07, Vmax=2.43±0.11Ltws-1 and 1/G=0.69±0.13 (N=8), where P* is the intercept on the force axis expressed relative to Ptw, peak isometric twitch force, Vmax is the intercept on the velocity axis, Ltw is the length at which Ptw is produced and G is the constant expressing curvature. The large values of 1/G indicate that the force­velocity relationship is not very curved. Maximum power was produced during shortening at 0.45±0.03Ptw (N=8). Maximum power during twitch contraction was 18.3±1.7mWg-1wetmass or, expressed in relative units, (V/Vmax)(P/Ptw), where V is the velocity during shortening and P is the force during shortening, was 0.16±0.01 (N=8), which is higher than that of many cross-striated locomotor muscles.

Journal Article↗
PubMed1996

Characterization of DRP2, a novel human dystrophin homologue.

The currently recognised dystrophin protein family comprises the archetype, dystrophin, its close relative, utrophin or dystrophin-related protein (DRP), and a distantly related protein known as the 87K tyrosine kinase substrate. During the course of a phylogenetic study of sequences encoding the characteristic C-terminal domains of dystrophin-related proteins, we identified an unexpected novel class of vertebrate dystrophin-related sequences. We term this class dystrophin-related protein 2 (DRP2), and suggest that utrophin/DRP be renamed DRP1 to simplify future nomenclature. DRP2 is a relatively small protein, encoded in man by a 45 kb gene localized to Xq22. It is expressed principally in the brain and spinal cord, and is similar in overall structure to the Dp116 dystrophin isoform. The discovery of a novel relative of dystrophin substantially broadens the scope for study of this interesting group of proteins and their associated glycoprotein complexes.

Amino Acid Sequence↗
PubMed1994

On the respiratory flow in the cuttlefish sepia officinalis.

The respiratory flow of water over the gills of the cuttlefish Sepia officinalis at rest is produced by the alternate activity of the radial muscles of the mantle and the musculature of the collar flaps; mantle circular muscle fibres are not involved. Inspiration takes place as the radial fibres contract, thinning the mantle and expanding the mantle cavity. The rise in mantle cavity pressure (up to 0.15 kPa), expelling water via the siphon during expiration, is brought about by inward movement of the collar flaps and (probably) mainly by elastic recoil of the mantle connective tissue network 'wound up' by radial fibre contraction during inspiration. Sepia also shows a second respiratory pattern, in which mantle cavity pressures during expiration are greater (up to 0.25 kPa). Here, the mantle circular fibres are involved, as they are during the large pressure transients (up to 10 kPa) seen during escape jetting. Active contraction of the muscles of the collar flaps is seen in all three patterns of expulsion of water from the mantle cavity, electrical activity increasing with increasing mantle cavity pressures. Respiratory expiration in the resting squid Loligo vulgaris is probably driven as in Sepia, whereas in the resting octopus Eledone cirrhosa, the mantle circular musculature is active during expiration. The significance of these observations is discussed.

Journal Article↗
PubMed1991

Morphology and electrical properties of Schwann cells around the giant axon of the squids Loligo forbesi and Loligo vulgaris.

The first successful dye-fills of Schwann cells around the split giant axon of Loligo show them to be spindle-shaped cells ca. 600 microns long and 20 microns wide lying parallel to the axonal axis. There are some 50,000 Schwann cells per cm2 of axonal membrane. Only a small part (ca. 6% of each Schwann cell membrane) is in contact with the periaxonal space, the remainder is overlain by adjacent Schwann cells, or applied to the basal lamina. The mean membrane potential of the Schwann cells in artificial seawater (ASW) varies from around -40 mV in fresh split-axon preparations to around -60 to -70 mV after 1-2 h; this hyperpolarization is not seen in preparations dissected and maintained in Ca2(+)-free ASW. Electrical- and dye-coupling (abolished by prior octanol treatment) is present between Schwann cells, but is weaker in cells with lower (less negative) membrane potentials. The implications for potassium homeostasis around the axon are briefly discussed.

Animals↗
PubMed1989

Epithelial action potentials in embryos of the Australian lungfish.

The epithelial cells of the skin of embryonic Australian lungfish (Neoceratodus forsteri) between stages 30 and 39, are mechanosensitive and excitable, showing overshooting action potentials 400-800 ms long with a rapid rise followed by a slower repolarization (usually with a shoulder on the repolarizing phase), which propagate at around 10 mm s-1. This skin impulse system is very similar to that found in embryonic and larval Amphibia; the significance of this similarity is discussed.

Action Potentials↗
PubMed1986

Contractile properties and ultrastructure of three types of muscle fibre in the dogfish myotome.

Three main types of fibre can be differentiated in the adult dogfish myotome at the immediate post-anal level. An outer band of muscle consists of 80-90 pale multiply innervated fibres (superficial fibres). These fibres are 80-90 micron in diameter, lack M-lines and have a low Ca2+-activated myosin ATPase activity. Volume densities of myofibrils (Vv(my,f] and mitochondria (Vv(mt,f] are respectively 76 and 9.5%. Beneath this layer are around 8000 red multiply innervated fibres. These have an average diameter of 25-40 micron. Vv(my,f) and Vv(mt,f) are 62 and 21% respectively, and M-lines are present. Around 11 000 white focally innervated twitch fibres lie beneath the red fibre zone. White fibres with an average diameter of 80-120 micron have a high Ca2+-activated myosin ATPase activity and Vv(my,f) and Vv(mt,f) are 78 and 5% respectively. Contractile properties of single skinned fibres were determined at 12 degrees C. Maximum Ca2+ activated tensions (kN m-2) and unloaded contraction speeds (muscle lengths s-1) were 49 and 0.5 for superficial, 70 and 1.4 for red and 180 and 4.4 for white muscle fibres. Superficial fibres have not been reported in other elasmobranchs with the exception of the closely related nursehound (Scyliorhinus stellaris L.) It is suggested that they are specialized for sustained force generation, having a tonic (postural) rather than a locomotor role.

Animals↗
PubMed1985

Locomotor adaptations of some gelatinous zooplankton.

Swimming behaviour and locomotor adaptations are described in chaetognaths, larvacean tunicates, some cnidaria, and thaliacean tunicates. The first two groups swim by oscillating a flattened tail, the others by jet propulsion. In chaetognaths, the locomotor muscle fibres are extensively coupled and relatively sparsely innervated, they exhibit compound spike-like potentials. The motoneurons controlling the rhythmic activity of the locomotor muscle lie in a ventral ganglion whose organization is briefly described. Rhythmic swimming bursts in larvaceans are similarly driven by a caudal ganglion near the base of the tail, but each caudal muscle cell is separately innervated by two sets of motor nerves, as well as being coupled to its neighbours. The external epithelium is excitable, and linked to the caudal ganglion by the axons of central cells. Mechanical stimulation of the epithelium evokes receptor potentials followed by action potentials and by bursts of rapid swimming. The trachyline medusa Aglantha and the small siphonophore Chelophyes also show rapid escape responses; in Aglantha these are driven by a specialized giant axon system lacking in other hydromedusae, and in Chelophyes. Slow swimming in Aglantha apparently involves a second nerve supply to the same muscle sheets used in rapid swimming, whereas in Chelophyes slow swimming results from the activity of the smaller posterior nectophore. Slow swimming in siphonophores is more economical than the rapid responses. In the hydrozoan medusa Polyorchis (as in Chelophyes) action potentials in the locomotor muscle sheet change in shape during swimming bursts, and their duration is related to the size of the medusa; they are not simply triggers of muscular contraction. The two groups of thaliacean tunicates are specialized differently. Doliolum is adapted for single rapid jet pulses (during which it achieves instantaneous velocities of 50 body lengths s-l), whilst salps are adapted for slow continuous swimming. The cost of locomotion is greater in Doliolum. Few gelatinous zooplankton show special adaptations both for rapid escape movements, and for slow sustained swimming, those that do deserve further study.

Action Potentials↗
PubMed1980

Immunoreactive human calcitonin-like molecule in the nervous systems of protochordates and a cyclostome, Myxine.

A molecule very closely resembling human calcitonin immunologically and chromatographically was extracted from the nervous systems of several protochordates and a cyclostome, Myxine. The presence of human calcitonin-like molecules in the nervous systems of primitive chordates suggests that they have some function in the nervous system of these species and that the bone-regulating function of the calcitonins may have arisen much later in the vertebrates.

Animals↗
PubMed1977

Locomotion and propagated skin impulses in salps (Tunicata: Thaliacea).

1. Various observations by M. Fedele on the mechanism of forward and reverse locomotion, on the neurogenic origin of the locomotor rhythm and on the coordinated behavior of salp chains are confirmed or extended. Salpa fusiformis was the species chiefly studied. 2. The striated muscle fibers of the body wall exhibit nonpropagative, graded responsivity. The fibers are multiply-innervated. Adjacent fibers are not electrically coupled. 3. Intracellular recordings are reported from a pacemaker and presumed motor neurons in the brain. The locomotor rhythm is exhibited by deafferented and isolated brains. In the intact animal, sensory input can modify the rhythm and alter the firing sequence of the muscles. The rhythm is accelerated by reduction, and inhibited by elevation of the ambient light intensity. 4. The outer skin is a conducting epithelium. The cells conduct action potentials at ca. 17 cm/sec and are connected by gap junctions. Three other independently conducting inner epithelial territories are described. Propagated impulses in the excitable epithelia are believed to enter the nervous system via neurosensory processes in the skin, extending the effective fields of these receptors. 5. Salp chains show coordinated responses but, except in their earliest developmental stages, impulses are probably not through-conducted along the chain, but are relayed from one zooid to the next by an unknown mechanism. 6. Comparisons are drawn between salps and other pelagic tunicates where conducting epithelia have previously been reported.

Action Potentials↗
PubMed1976

Stretch receptors in urodele limb muscles.

Non-encapsulated, fine beaded nerve endings were found histologically on some muscle fibres in a number of limb muscles in newts and axolotls. They were present in newt muscles that had been chronically de-efferented, and in which no efferent activity survived, and were therefore likely to be sensory. They were located only on muscle fibres on or near the outside surface of the muscle. These small-diameter muscle fibres were characterised histochemically by low lipid, SDH and phosphorylase content; ultrastructurally by low glycogen content, and relatively large myofilaments poorly delimited by a sparse SR. There were many of this type (Type 1) that did not support sensory endings. A few endings occurred on another larger-diameter type of fibre (Type 2) whose properties were opposite to those listed above for Type 1. There was virtually no specialization of muscle fibre structure beneath the sensory endings. Physiological experiments involving ramp-and-hold and sinusoidal stretch applied to the muscle whilst recording single-unit afferent responses in m.ext. dig. III of axolotls showed unit responses very similar to those known from muscle spindles, particularly those of the frog.

Action Potentials↗