Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Decapodiformes”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10Linked to original sources
PubMed1980

Autorhythmicity and entrainment in excitable membranes.

Low calcium increases the excitability of neurones and can induce autorhythmicity in excitable cells. Numerical solutions of the Hodgkin-Huxley membrane equations, and numerical evaluations of the small-signal impedance and admittance are used to illustrate the increase in resonance produced by low [Ca2+]0. The resonant frequency may be located either by the peak of the amplitude of the impedance, or by the frequency at which the phase angle is zero for 1 : 1 entrained action potentials. Autorhythmicity is produced by any mechanism which increases the resonant peak of the amplitude of the membrane impedance.

Animals↗
PubMed1985

A new algorithm for voltage clamp by iteration: a learning control of a nonlinear neuronal system.

Voltage-clamp of excitable membrane allows the measurement of membrane currents associated with electrical potential changes across the membrane. However, it has been impossible in practice to apply the conventional analog feedback voltage-clamp circuits to single electrode voltage clamping in central neurons. The reason for this is that the feedback system becomes unstable because of the positive feedback required for compensation of capacitative loss through the wall of the microelectrode. Park et al. (1981) proposed a new iterative technique to solve this problem. It requires that the potential to be clamped repeats itself with little or no change. The amount of current needed to clamp the membrane potential is not determined at once, but in a step-wise, trial and error fashion in the course of a set of repetitions. Since the feedback loop is open in real time, the system has great stability, and this advantage can be exploited in single electrode preparations. The computation algorithm which calculates the current waveform based on the voltage deviation during the last trial is the central part of the iterative voltage-clamp system. In this paper, we propose a new algorithm, which has several theoretical and practical advantages over the original one proposed by Park et al. First, two parameters used in the new algorithm are predetermined by a current-clamp experiment. Second, the speed of convergence of the new algorithm is faster than that of the Park's original algorithm. This was shown by computer simulation of iterative voltage clamp of artificial membrane following Hodgkin-Huxley equations for squid axon membrane and Rall's compartment model for a neuron with dendrites. Finally, we offer proof that the new algorithm is certain to converge for the general cases of voltage-clamp experiments with active membrane properties, synaptic membranes, etc. Consequently, the new algorithm for iterative voltage clamp is very suitable for single electrode voltage clamp in the central neurons. The new algorithm has been successfully applied to voltage-clamp experiments on rubrospinal neurons of cats (Tsukahara, Murakami, Kawato, Oda, and Etoh, in preparation).

Animals↗
PubMed1988

Squid glycoproteins with structural similarities to Thy-1 and Ly-6 antigens.

In an attempt to identify invertebrate homologs of Thy-1 antigen, the optic and central nervous tissue of squid was solubilized in deoxycholate and fractionated by lentil lectin affinity chromatography and gel filtration to yield small abundant glycoproteins. Material with biochemical similarities to Thy-1 was found and shown to consist of two glycoproteins that were ultimately purified using monoclonal antibody affinity columns. Both glycoproteins were sequenced to yield sequences of 84 residues for Sgp-1 and 92 residues for Sgp-2. The sequences were analyzed for similarities to Thy-1 and other Ig-related sequences, and Sgp-1 showed some similarities that were greater than 3 standard deviation units away from mean random scores when tested with the ALIGN program. However, the sequence patterns were not typical of Ig-related domains and the relationship of Sgp-1 to the Ig superfamily remains problematical. Sgp-2 showed no relationship to the Ig superfamily, but similarities to Ly-6 antigen sequences were noted that are in accord with an evolutionary relationship. The similarities included ten Cys residues in each sequence of which eight were matched in the best alignment given by the ALIGN program. Chemical evidence was obtained for glycophospholipid tails at the COOH-termini of Sgp-1 and Sgp-2 as is the case for Thy-1 and Ly-6 antigens.

Amino Acid Sequence↗
PubMed1975

Cytochemical localization of cholinesterase activity at the giant synapse of the squid.

The giant synapse of squid stellate ganglion is a chemical synapse where the transmitter substance is not known. The components of the ACh-system are present in squid nervous tissue in large quantities. However externally applied cholinergic drugs have no effect on junctional transmission. Using the Copper thiocholine method for electron microscopic cytochemistry the reaction product was found at the axolemmal surface, in the cisternae of the endoplasmic reticulum of neurons and occasionally between the infoldings of the sheat cells surounding the axons. Abundant deposits of end product are observed in the extracellular space in the proximity to junctional region. However, the localization of the cytochemical end product at the junctional region proper was observed frequently, but not consistently. Radiometric measurements of enzyme activity have revealed that neither specific inhibitors nor specific substrates generaly used for differentiation of cholinesterases in mammalian nervous tissue can be employed for differentiation of squid enzymes. Considering the permeability barriers imposed for external acetylcholine by cytoplasmic processes and the high enzyme activity of structures surrounding the giant synapse, the possibility that acetylcholine may still be a candidate for the missing transmitter is discussed.

Animals↗
PubMed1975

Fluorescence polarization studies of squid giant axons stained with N-methylanilinonaphthalenesulfonates.

The polarized components of the extrinsic fluorescence of squid giant axons stained with 2,6-MANS or 1,8-MANS were studied. The polarization properties of the fluorescence changes associated with voltage-clamp pulses were found to be very different from those of the static fluorescence, supporting the notion that the optical changes involve highly oriented membrane adsorbed fluorophores. The theoretical expectations according to this hypothesis are discussed in detail. The experimental results are in good agreement with the theory assuming that possible probes reorientations are soley due to the action of the applied electric field upon the probes electric dipole. The quantitative analysis of the data for 2,6-MANS provides a fairly accurate determination of the orientation of the membrane bound 2,6-MANS molecules responsible for the fluorescence changes. Such orientation appears to be independent of the membrane face exposed to staining. The data for 1,8-MANS indicate a very different orientation of this isomer. The results suggest a profitable use of extrinsic fluorophores for studies of the structural organization of nerve membranes.

Anilino Naphthalenesulfonates↗
PubMed1978

Two components of extracellularly-recorded photoreceptor potentials in the cephalopod retina: differential effects of Na+, K+ and Ca2+.

The ERG of the isolated, superfused half-eye of the cephalopod Sepiola atlantica, evoked by a brief (10 micro second) light flash, has been studied by recording intraretinal potentials with glass microelectrodes. The intensity-response characteristics of the potentials recorded at an electrode fixed at the surface (Vs) can be fitted by a simple equation derived from an equivalent circuit model based on a sodium conductance increase mechanism. Raising the external potassium level reduces the maximal response (deltaVm), but does not alter the half-saturation intensity value (I0). Reducing external sodium does not affect deltaVm, but increase I0. Reducing external calcium also does not affect delta Vm, but decrease I0. These effects are adequately described by the model if it is also assumed (a) that changing the external sodium does not significantly alter the transmembrane sodium gradient, and (b) that sodium and calcium ions compete for the sensitivity control mechanism. Differential-depth recording between the fixed electrode at the surface and another electrode that could be moved into the retina revealed that the two component appearance of the transretinal ERG arose from the superposition of two vitreal-negative waveforms. An initial "fast" component was mainly recorded in the photoreceptive distal segments while a "slow" component was prominent in the more proximal regions of the retina. Perfusion with high K+ salines resulted in a decrease in the amplitudes of both fast and slow components of the response whereas reducing external Na+ reduced the amplitude of the fast component at all light intensities but reduced the amplitude of the slow component only at low intensities. The amplitudes of both the fast and slow components increased on reducing external calcium, but the rate of rise and fall of the fast component was independent of external calcium. The rate of rise of the slow component was also independent of the external Ca2+ level but a minimum in the recovery time (tF) was shifted to a lower intensity value at lower calcium concentrations. The shift of the minimum was to a higher intensity value with lowered sodium perfusing solutions. On the basis of the differential sensitivity of the two components to ion changes, as well as stimulus intensity and intraretinal distribution of the components, it is suggested that they reflect two distinct processes in the light-evoked potential of the photoreceptor cells.

Animals↗
PubMed1990

Physiological color change in squid iridophores. I. Behavior, morphology and pharmacology in Lolliguncula brevis.

Cephalopods generally are thought to have only static iridophores, but this report provides qualitative and quantitative evidence for active control of certain iridescent cells in the dermis of the squid Lolliguncula brevis. In vivo observations indicate the expression of iridescence to be linked to agonistic or reproductive behavior. The neuromodulator acetylcholine (ACh) induced dramatic opitcla changes in active iridophores in vitro, whereas ACh had little effect on passive iridophores elsewhere in the mantle skin. Bath application of physiological concentrations of ACh (10(-7)M to 10(-6)M) to excised dermal skin layers transformed the active iridophores from a non-reflective diffuse blue to brightly iridescent colors, and this reaction was reversible and repeatable. The speed of change to iridescent in vitro corresponded well to the speed of changes in the living animal. Pharmacological results indicate the presence of muscarinic receptors in this system and that Ca++ is a mediator for the observed changes. Although ACh is present in physiological quantities in the dermal iridophore layer, it is possible that ACh release is not controlled directly by the nervous system because electrophysiological stimulation of major nerves in the periphery resulted in no iridescence in L. brevis; nor did silver staining or transmission electron microscopy reveal neuronal elements in the iridophore layer. Thus, active iridophores may be controlled by ACh acting as a hormone.

Acetylcholine↗
PubMed1990

Physiological color change in squid iridophores. II. Ultrastructural mechanisms in Lolliguncula brevis.

Evidence is presented that changes in the optical properties of active iridophores in the dermis of the squid Lolliguncula brevis are the result of changes in the ultrastructure of these cells. At least two mechanisms may be involved when active cells change from non-iridescent to iridescent or change iridescent color. One is the reversible change of labile, detergent-resistant proteinaceous material within the iridophore platelets, from a contracted gel state (non-iridescent) to an expanded fluid or sol state when the cells become iridescent. The other is a change in the thickness of the platelets, with platelets becoming significantly thinner as the optical properties of the iridophores change from non-iridescent to iridescent red, and progressively thinner still as the observed iridescent colors become those of shorter wavelengths. Optical change from Rayleigh scattering (non-iridescent) to structural reflection (iridescent) may be due to the viscosity change in the platelet material, with the variations in observed iridescent colors due to changes in the dimensions of the iridophore platelets.

Acetylcholine↗
PubMed1986

Capture, transport, and maintenance of live squid (Loligo pealei) for electrophysiological studies.

The capture, transport, and maintenance of live adult Atlantic coast squid (Loligo pealei) are described. The objective was to obtain healthy live squid from a coastal region and to maintain them at an inland research facility long enough to provide at least 4 days of electrophysiological research. An inexpensive closed aquarium system is described, which utilizes an ion-exchange resin in the filter, that allows a typical survival time of at least 4.5 days. Similar closed aquarium systems may be of interest to other biophysicists who wish to maintain live squid away from coastal research facilities.

Animal Husbandry↗
PubMed1987

Local anaesthetic effects of benzene and structurally related molecules, including benzocaine, on the squid giant axon.

(1). The effects of benzene and several of its derivatives on sodium currents in the voltage-clamped squid giant axon have been studied. Substances tested were benzene, aniline, benzyl alcohol, propiophenone, 4-amino-propiophenone, methyl benzoate, ethyl benzoate, and 4-amino ethyl benzoate (benzocaine). (2.) All substances tested reduced the sodium current in both intact axons and axons internally perfused with CsF. (3.) There were four major actions of benzene on the sodium current: (a) an increase in the resting level of inactivation, (b) an increase in the depolarization required to produce the maximum current, (c) a decrease in the maximum sodium conductance, and (d) an increase in the rate of inactivation. (4.) 4-amino ethyl benzoate (benzocaine) had actions on the sodium current which were very similar to those of benzene with the exception that the rate of inactivation was scarcely affected and, at comparable shifts, the slope of the steady state inactivation curve was slightly smaller. (5.) The results obtained with the substances structurally intermediate between benzene and 4-amino ethyl benzoate allow some conclusions to be drawn as to the role of each functional group.

Anesthetics, Local↗
PubMed1987

The mechanisms of sodium current inhibition by benzocaine in the squid giant axon.

(1) The effects of benzocaine on the ionic currents in the voltage-clamped squid giant axon have been examined under various conditions; intact axons, axons internally perfused with CsF and axons dialysed with tetraethylammonium ions were used. (2) Both the steady state outward (potassium) current and the early transient (sodium) current were reduced by ca. 50% by benzocaine (1 mM). (3) Plots of the changes produced by benzocaine (1 mM) in the Hodgkin-Huxley parameters for the steady state activation (m infinity), the steady state inactivation (h infinity) and the time constants (tau m and tau h) for activation and inactivation of the sodium current are shown. The m infinity and h infinity curves are shifted in positive and negative directions respectively on the voltage axis. The time constants are not greatly affected. (4) In axons in which the sodium current inactivation had been largely removed by treatment with chloramine T, the sodium current was still reduced by ca. 50% by 1 mM benzocaine and the positive shift in activation remained unchanged. (5) The dependence on benzocaine concentration (for less than or equal to 2 mM) of the peak sodium current reduction and the shift in steady state inactivation have been determined. (6) It is concluded that in the squid axon the effects on inactivation are not the main reason for the reduction of the sodium current by benzocaine and that, in common with many other neutral anaesthetics, there are at least two sites at which benzocaine acts.

Animals↗
PubMed1982

Electrical responses to mechanical stimulation of the membrane of squid giant axons.

The mechano-electrical transduction in the squid axon was studied. A certain volume of solution was intracellularly injected, subsequently redrawn, by a microsyringe, and the resultant expansion and shrinkage of the cell was employed as the mechanical stimulus. Upon stimulation, two types of responses appeared: a depolarizing response and a hyperpolarizing response. The former appeared on large stimulation, but the shape and magnitude were variable even with the same stimulation, and the recovery was very slow. The latter appeared constantly on small stimulation. This hyperpolarizing response was associated with an increase in membrane conductance. Application of inward current through the membrane reversed the sign of the response. The reversal potential was 5-15 mV more negative than the resting potential. It was greatly affected by extracellular K+ concentration. Tetraethylammonium, applied intracellularly, reduced the amplitude of the hyperpolarizing response. However, 4-aminopyridine, tetrodotoxin, and procaine did not affect the response at all. The response became larger when the temperature was reduced. It is possible that the mechanically-induced hyperpolarizing response arises from an increase of potassium and leakage conductance.

Animals↗
PubMed1988

A lateral line analogue in cephalopods: water waves generate microphonic potentials in the epidermal head lines of Sepia and Lolliguncula.

Many cephalopods have lines of ciliated cells on their head and arms. In the cuttlefish Sepia and the squid Lolliguncula, electrophysiological recordings clearly identify these epidermal lines as an invertebrate analogue to the mechanoreceptive lateral lines of fish and aquatic amphibians and thus as another example of convergent evolution between a sophisticated cephalopod and vertebrate sensory system. Stimulation of the epidermal lines with local water displacements, generated by a vibrating sphere, causes receptor potentials that have many features known from lateral line microphonic potentials. The minimal threshold of the head lines is 0.2 micron peak-to-peak water displacement (calculated at the skin surface) at 75-100 Hz.

Action Potentials↗