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At least 217 records · Page 12Linked to original sources
PubMed1992

Macroelements content of Common Pacific squid (Loligo opalescens).

The macroelement (sodium, potassium, calcium and magnesium) concentrations have been determined in various tissues of the Common Pacific squid, Loligo opalescens. The method of measurement was flame atomic emission (sodium and potassium) and absorption (calcium and magnesium) spectrometry. Edible tissues such as the tube (mantle), arms and crown, and fin contained: from 3.3 +/- 0.4 to 3.9 +/- 1.5 (1.9-6.8) g/kg wet weight of sodium; from 5.3 +/- 0.6 to 6.3 +/- 2.7 (3.3-14) g/kg of potassium; 38 +/- 7 to 100 +/- 34 (28-200) mg/kg of calcium; and from 510 +/- 100 to 950 +/- 280 (340-1500) mg/kg of magnesium. The other tissues or organs examined frequently contained a higher concentration of macroelements than the edible flesh. Statistically significant correlations between the body weight of squid and macroelement concentrations or between some pairs of metals in whole squid, mantle and hepatopancreas have been observed.

Animals↗
PubMed1995

Cytoplasmic constriction and vesiculation after axotomy in the squid giant axon.

The squid giant axon responded to a transection injury by producing a gradient of cytoplasmic and vesicular changes at the cut end. At the immediate opening of the cut axon the cytoplasm was fragmented and dispersed and the vesicles in this region were in rapid Brownian movement. Approximately 0.1 mm further in, at the site of maximal axonal constriction, the axoplasm was condensed into a compact, constricted mass containing many large vesicles. The axoplasm was normal a few millimetres beyond this constricted, vesiculated end. It appears that transection triggered the transformation of normal axoplasm into a tightly constricted, highly vesiculated structure. This modified axoplasm at the cut end may slow the spread of damage and degeneration by preventing the bulk outflow of axoplasm, by slowing down the loss of intracellular molecules and by slowing down the influx of destructive extracellular ions (like calcium and chloride).

Animals↗
PubMed1991

The quantal gating charge of sodium channel inactivation.

Using a very low noise voltage clamp technique it has been possible to record from the squid giant axon a slow component of gating current (Ig) during the inactivation phase of the macroscopic sodium current (INa) which was hitherto buried in the baseline noise. In order to examine whether this slow Ig contains gating charge that originates from transitions between the open (O) and the inactivated (I) states, which would indicate a true voltage dependence of inactivation, or whether other transitions contribute charge to slow Ig, a new model independent analysis termed isochronic plot analysis has been developed. From a direct correlation of Ig and the time derivative of the sodium conductance dgNa/dt the condition when only O-I transitions occur is detected. Then the ratio of the two signals is constant and a straight line appears in an isochronic plot of Ig vs. dgNa/dt. Its slope does not depend on voltage or time and corresponds to the quantal gating charge of the O-I transition (qh) divided by the single channel ionic conductance (gamma). This condition was found at voltages above -10 mV up to +40 mV and a figure of 1.21 e- was obtained for qh at temperatures of 5 and 15 degrees C. At lower voltages additional charge from other transitions, e.g. closed to open, is displaced during macroscopic inactivation. This means that conventional Eyring rate analysis of the inactivation time constant tau h is only valid above -10 mV and here the figure for qh was confirmed also from this analysis. It is further shown that most of the present controversies surrounding the voltage dependence of inactivation can be clarified. The validity of the isochronic plot analysis has been confirmed using simulated gating and ionic currents.

Animals↗
PubMed1988

Transglial pathway of diffusion in the Schwann sheath of the squid giant axon.

In order to investigate the transglial pathways in the Schwann sheath of squid giant axons, an electron microscopic study of thin sections and freeze-fracture replicas was carried out. Hitherto the mesaxonal clefts between Schwann cells were regarded as the only pathway between the extracellular space and the periaxonal space which, like the clefts, is about 10 nm in width. The clefts were now found to be obstructed by a putative single-stranded tight junction between neighbouring Schwann cells along the entire border near the axon. The Schwann cells were found to be penetrated like a sponge by a three-dimensional tubular transglial lattice that is confluent with the periaxonal space, the mesaxonal clefts and the extracellular space. The transglial channel system (TGCS) would, therefore, serve as an alternative diffusional pathway, provided that the tubular lumen was permeable. The diameter of the tubules is about 40 nm. In freeze-fracture replicas the density of tubular openings towards the axon was estimated to be 3.3 +/- 0.72 per micron 2. In relation to the periaxonal cell surface, this constitutes a relative opening area of 0.42% as compared to the 0.15% of the mesaxonal clefts (neglecting their tight junctions). Therefore, the TGCS would provide a ubiquitous access for ionic flow between axolemma and extracellular space. The fact that the TGCS has only recently been observed in squid, but has been described for some time in the giant nerve fibres of crayfish and lobster, can be explained by the use of different fixation methods. The TGCS system is preserved in aldehyde fixation as used in the present study, whereas osmium tetroxide was applied in earlier work on squid. The comparison with the results obtained in other species suggests strongly that the TGCS is permeable and constitutes a transglial pathway for rapid ionic flow.

Animals↗
PubMed1979

The phylogenetic distribution of tubulin:tyrosine ligase.

The post-translational addition of tyrosine to alpha-tubulin, catalyzed by tubulin:tyrosine ligase, has been previously reported in mammals and birds. The present study demonstrated that significant ligase activity was present in representative organisms from several other major vertebrate classes (chondrichthyes through reptiles) and that both substrate and enzyme from all vertebrates investigated were compatible with mammalian ligase and tubulin in the tyrosination reaction. None of the invertebrate tissues examined showed incorporation of tyrosine, phenylalanine or dihydroxyphenylalanine into alpha tubulin under conditions allowing significant incorporation of these compounds in vertebrate supernatant samples. The failure of invertebrate tubulin to incorporate tyrosine in vitro did not appear to be due to saturation of the carboxyl terminal position with tyrosine or the presence of a soluble inhibitor of ligase activity. Although tubulin amino acid composition has been highly conserved throughout evolution, a major evolutionary divergence is described based upon biochemical differences whereby invertebrate tubulin cannot be tyrosinated or post-translationally modified with phenylalanine or dihydroxyphenylalanine under conditions suitable for the incorporation of these compounds by vertebrate alpha tubulin.

Animals↗
PubMed1977

Internal and external application of photodynamic sensitizers on squid giant axons.

Squid giant axons were photosensitized by dyes applied internally or externally in air saturated solutions and photochemically modified by visible light. For most dyes the modifications included an irreversible block of sodium channels, a destruction of inactivation in some of the unblocked channels, and a slowing of inactivation. Internal application was up to 100-fold more effective in blocking sodium channels than external application, suggesting a site of block nearer the internal surface. Rose Bengal sensitized channel block and destruction of inactivation when applied internally, but sensitized only channel block when applied externally. In contrast, externally applied Eosin Y sensitized a clear slowing of inactivation plus channel block. Beta-carotene, an effective agent for quenching photochemically generated excited singlet oxygen, inhibited most of the modification sensitized by internally applied Methylene blue but not by Rose Bengal or Merocyanine 540.

Action Potentials↗
PubMed1975

Sodium-calcium exchange and calcium-calcium exchange in internally dialyzed squid giant axons.

The influx and efflux of calcium (as 45Ca) and influx of sodium (as 24Na) were studied in internally dialyzed squid giant axons. The axons were poisoned with cyanide and ATP was omitted from the dialysis fluid. The internal ionized Ca2+ concentration ([Ca2+]i) was controlled with Ca-EGTA buffers. With [Ca2+]i greater than 0.5 muM, 45Ca efflux was largely dependent upon external Na and Ca. The Nao-dependent Ca efflux into Ca-free media appeared to saturate as [Ca2+]i was increased to 160 muM; the half-saturation concentration was about 8 muM Ca2+. In two experiments 24Na influx was measured; when [Ca2+]i was decreased from 160 muM to less than 0.5 muM, Na influx declined by about 5 pmoles/cm2 sec. The Nao-dependent Ca efflux averaged 1.6 pmoles/cm2 sec in axons with a [Ca2+]i of 160 muM, and was negligible in axons with a [Ca2+]i of less than 0.5 muM. Taken together, the Na influx and Ca efflux data may indicate that the fluxes are coupled with a stoichiometry of about 3 Na+-to-1 Ca2+. Ca efflux into Na-free media required the presence of both Ca and an alkali metal ion (but not Cs) in the external medium. Ca influx from Li-containing media was greatly reduced when [Ca2+]i was decreased from 160 to 0.23 muM, or when external Li was replaced by choline. These data provide evidence for a Ca-Ca exchange mechanism which is activated by certain alkali metal ions. The observations are consistent with a mobile carrier mechanism which can exchange Ca2+ ions from the axoplasm for either 3 Na+ ions, or one Ca2+ and an alkali metal ion (but not Cs) from the external medium. This mechanism may utilize energy from the Na electrochemical gradient to help extrude Ca against an electrochemical gradient.

Animals↗