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At least 307 records · Page 17Linked to original sources
PubMed1981

Ca-K bi-ionic action potential in squid giant axons.

Under intracellular perfusion with a solution containing K+ as the sole cation species, squid giant axons were found to be capable of developing all-or-none action potentials when immersed in a medium in which CaCl2 was the only electrolyte. The adequate range of ion concentration for demonstrating this capability was mentioned. The reversal potential level measured by the voltage-clamp technique varied directly with the logarithm of the concentration of extracellular Ca-ion; the proportionality constant was close to RT/2F. The action potential observed under this Ca-K bi-ionic condition could not be suppressed by addition of tetrodotoxin or saxitoxin to the external medium. The external Ca-ion could be replaced with Co- or Mn-ion without eliminating the capability of the axons to develop action potentials. D-600 could not suppress the inward current observed under the voltage-clamp condition, but 4-aminopyridine could suppress it. The experimental findings were interpreted based on the current channel hypothesis and on the macromolecular theory.

4-Aminopyridine↗
PubMed1981

Periodic responses in squid axon membrane exposed intracellularly and extracellularly to solutions containing a single species of salt.

A periodic membrane potential change was found to occur in squid giant axons which were internally and externally perfused with solutions of an identical composition and were hyperpolarized by passing a sustained inward current. The solution contained Co2+ or Mn2+ as the sole cation species at a concentration of 1-10 mM. The amplitude of the response was roughly 100 mV. The current intensity and the ion concentration had large effects on the response. The voltage-clamp technique revealed an N-shaped I-V characteristic of the membrane system. The membrane emf of the resting and excited states was almost the same but the membrane conductance was increased in the excited states. The response was suppressed with 4-aminopyridine reversibly but unchanged with tetrodotoxin or D-600. Those unusual ionic conditions did not deprive axons of their ability to produce ordinary action potentials in physiological solutions. The experimental conditions employed and the results obtained were very close to those for some of the artificial membrane models. Applicability of the physico-chemical theories developed for these models is discussed.

Animals↗
PubMed1983

Subcellular distribution and binding of heavy metals in the untreated liver of the squid; comparison with data from the livers of cadmium and silver-exposed rats.

In natural squid liver, about 30% of the total Cd present was found in the cytosolic fraction. A large portion of this Cd was bound to high molecular weight species (mol. wt greater than 70,000). In contrast to Cd, about 60% of the total Ag occurred in the cytosolic fraction; Ag was bound mainly to low molecular weight species (mol. wt less than 20,000).

Animals↗
PubMed1976

In vitro accumulation of mineral components by invertebrate cartilage.

In vitro mineralization of the gill cartilage of Limulus (horse-shoe crab) has been reported previously (Eilberg et al. 1975). The present study demonstrates that cranial cartilage of Loligo (squid) and odontophore cartilage of Busycon (marine snail) also mineralize in vitro in hydroxyapatite-metastable media, but not in carbonate-metastable media. In all three of these cartilages, light phase-contrast microscopy revealed that the mineral phase occured in the form of spherical or ovoid granules ranging between 2 and 9 mum in diameter. During mineralization, the granules appeared successively in the perichondrium, in the matrix, and finally, within chondrocytes. Mineralization occurred more rapidly in Eusycon odontophore cartilage which has a significantly higher content of phosphatidyl serine than in Limulus gill or Loligo head cartilages. In all tissues the mineralization process is related to temperature, taking place most actively at 37 degrees C and only weakly at 50 degrees C.

Animals↗
PubMed1977

Trace metal concentrations and partitioning in zooplankton, neuston, and benthos from the south Texas outer continental shelf.

A variety of marine biota, including zooplankton, sargassum, surface plankton, squid, shrimp, and fish collected along the south Texas Outer Continental Shelf, were analyzed for Cu, Zn, Cd, Pb, Cr, Ni, Fe, and Mn. Although there is a great deal of variation in the chemical content of the various samples, both within species and between species, the variations all fall within the range of values published for similar organisms collected elsewhere. An increase in Pb concentration from north to south, and an increase in Cd concentration from nearshore to further offshore in the zooplankton mirrors the sediment patterns. Statistical analysis of the chemical and biological data for these samples indicates that relatively small percentages of the biological makeup of the sample can markedly affect the concentrations of Pb, Cd, Ni, and Zn. This is particularly true for the larvacea, ostracoda, and mollusca. Chemical analyses of the exoskeletons of shrimp and the skin of both squid and fish indicate that they generally contain higher metal levels in comparison with the flesh from the same organism. This is probably the result of either adsorption from seawater and/or an internal detoxification procedure employed by the organism. The analysis of a composite sample of squid 'pens' indicates that they contain enriched Cu, Cd, Zn, Pb, and Fe levels in comparison with the skin and flesh. These elevated levels are probably the result of an internal detoxification procedure and/or may represent a means of storing necessary metabolites, at least in the case of Cu and Zn, but can not be attributed to adsorption as the chitinous 'pen' is imbedded in tissue and is not directly exposed to seawater.

Animals↗
PubMed1996

The structure of the neurofilament cytoskeleton in the squid giant axon and synapse.

Stereo views of thick sections (< 0.5 micron), or freeze etch replicas taken from selected regions of the squid giant axon and giant synapse, using an electron energy loss spectroscopic ultrastructural method, revealed a meshwork of anastomosing neurofilaments intersecting at a wide range of angles. This type of architectural organisation differs significantly from the ladder-like construction of the mammalian neurofilament cytoskeleton, in which longitudinally oriented core filaments are interconnected by lateral crossbridges. The deviant organization of squid neurofilaments is consistent with recent evidence that squid neurofilament proteins more closely resemble nuclear lamin rather than mammalian neurofilament proteins. A proximo-distal gradient of increasing width of the neurofilament meshes along the giant axon correlated well with the previously described gradient of increasing neurofilament phosphorylation. In these thick sections the presynaptic terminal of the giant synapse exhibited a mature neurofilament cytoskeleton that extended to the active zones without detectable signs of degradation. The observations are discussed in the context of current hypotheses concerned with the function of phosphorylation of neurofilaments, and with the steady state maintenance of the cytoskeleton in the squid axon and presynaptic terminal.

Animals↗
PubMed1975

The identification of dansyl sarcosine and its occurrence in molluscs.

An unknown dansyl derivative was identified as dansyl sarcosine. In molluscs, sarcosine was found to be largely localized to the nervous system. Examination of individual snail neurones, regions of the octopus brain and the squid giant synapse showed dramatic variations in sarcosine levels.

Animals↗
PubMed1987

Freeze-fracture studies on the giant axon and ensheathing Schwann cells of the squid.

The giant axons and encompassing sheaths from the stellar nerves of the squids Sepioteuthis sepioidea and Loligo forbesi have been analysed by freeze-fracture. The axolemma exhibits many intramembranous particles (IMPs) that fracture onto the cytoplasmic membrane half-leaflet (P-face); the larger IMPs may be aggregated into clusters. Axoplasmic subsurface cisternae are found beneath this membrane. Clustered or aligned arrays of P-face IMPs are also found on the membranes of the Schwann cells that intimately encapsulate the giant axons as well as 'capitate' projections of Schwann cells into the axons. When adjacent Schwann cells abut directly against one another, aligned E-face IMPs are found along the fracture plane of the upturning membranes. These E-face alignments of IMPs have complementary furrows on the Schwann cell membranes which exhibit no complementary structure on the axolemma as they represent the clefts between adjacent glial cells. The other Schwann cell membranes exhibit P-face dimples and E-face (extracellular membrane half-leaflet) protuberances which may reflect endo- or exocytotic activity; alternatively they may represent caveolae. Comparable structures are occasionally observed at axo-glial interfaces. However, those in the Schwann cell membrane could be part of the transverse tubular lattice system which also exists in adaxonal glia. Beyond the Schwann cells, layers of endoneurial cells (fibrocytes) are interleaved by collagen-filled spaces. These cells exhibit extensive cross-fractured intracellular invaginations as well as inpushings of the extracellular matrix material. Their membranes exhibit a large number of IMPs.

Animals↗
PubMed1987

Polarity orientations of microtubules in squid and lobster axons.

Polarity orientations of microtubules in periaxolemmal and internal regions of squid and lobster axons were determined in order to test the hypothesis that regional differences in particle transport are produced by differentially distributed microtubule subclasses. Over 95% of the microtubules in all regions of the axons investigated were oriented with plus ends located distally, pointing away from axonal somata, and there were no significant differences in orientation ratios in periaxolemmal and internal axoplasm. In axonal sheath glial cells of lobsters, microtubules were found to be oriented parallel to axonal microtubules and to have approximately equally mixed polarities. The results for axonal microtubules did not support the possibility of subclasses of axonal microtubules.

Animals↗