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At least 469 records · Page 26Linked to original sources
PubMed1986

Heat shock-like protein is transferred from glia to axon.

Glia-axon protein transfer was examined in the squid giant axon. Proteins synthesized by the glial sheath surrounding the axon were labeled with [3H]leucine. Raising the temperature of the incubation medium from 20 degrees C to 30 degrees C increased the synthesis of glial proteins that resembled heat-shock proteins. These proteins were among the group known to be transferred into the axon. Thus, glia provide the axon with proteins that may be involved in the reaction to trauma.

Animals↗
PubMed1986

Ion permeation and selectivity of squid axon sodium channels modified by tetramethrin.

The pyrethroid tetramethrin greatly prolongs the sodium current during step depolarization and the sodium tail current associated with step repolarization of the squid axon membrane. Non-linear current-voltage relationships for the sodium tail current were analyzed to assess the open sodium channel properties which included the permeation of various cations, calcium block and cation selectivity. Tetramethrin had no effect on any of these properties. It was concluded that tetramethrin modifies the sodium channel gating machinery without affecting the pore properties.

Animals↗
PubMed1986

Axonal transport and the movement of 45Ca inside the giant axon of squid.

45Ca was microinjected directly into the giant axon of squid, and the radioisotope profile along the axon was determined after 2-12 h. Our results indicated that the intracellular Ca ions at the axon, unlike those at the cell body, were not axonally transported at a fast rate. The implication of this finding on the involvement of Ca in the axonal transport system is discussed.

Animals↗
PubMed1987

ATP-dependent and ATP-independent calcium buffers determined in isolated squid axoplasm by axoplasmic dilution using calcium-selective electrodes.

Ca2+ buffering in axoplasm extruded from the squid giant axon was studied by axoplasmic dilution and Ca2+-selective electrodes. ATP-dependent Ca2+ buffering was lost when metabolism and endogenous ATP production were inhibited by axoplasmic dilution. Under these conditions ('low ATP' axoplasmic suspensions) Ca2+ activity (aCa) increased spontaneously. This increase was prevented by ATP addition. Addition of a Ca2+ load to axoplasmic suspensions following ATP addition ('normal ATP' axoplasmic suspensions) did not increase aCa. When a Ca2+ load was added to low ATP axoplasmic suspensions the value of aCa was only 5% of that expected from the Ca2+ load in a non-Ca2+ buffered system. Addition of the Ca2+ ionophore A23187 to Ca2+-loaded normal ATP axoplasmic suspensions increased aCa to a value 5% of that expected in a non-Ca2+ buffered system. Addition of A23187 or KCN to low ATP axoplasmic suspensions did not increase aCa above that produced by axoplasmic dilution. These data indicate the presence of ATP-dependent and ATP-independent Ca2+ buffering mechanisms in the squid axoplasm and that the ATP-dependent Ca2+ buffering was mediated by membrane-limited organelles presumably the mitochondria and endoplasmic reticulum.

Adenosine Triphosphate↗
PubMed1988

Interactions of pyrethroids and octylguanidine with sodium channels of squid giant axons.

Kinetics of pyrethroid-modified sodium channels and the interaction of N-octylguanidine with the modified channels have been studied with internally perfused and voltage-clamped squid giant axons. The pyrethroids used were 1R-cis-phenothrin; 1R-cis-permethrin; 1R-cis-cyphenothrin; and 1R-cis-deltamethrin. Modification of sodium channels by pyrethroids resulted in marked slowing of opening and closing kinetics. The rate at which sodium channels arrived at the open pyrethroid-modified state during a depolarizing step was independent of the concentration of pyrethroids applied. The time of exposure to pyrethroids required for the pyrethroid-induced sodium tail current following a step depolarization to reach a steady-state amplitude was independent of the frequency of short (5 ms) depolarizing pulses, and in the pronase-treated axons was independent of the membrane potential (0 mV or -90 mV). We conclude that sodium channels are modified by pyrethroids primarily in the closed resting state. A small fraction of sodium channels is modified in the open state. The dose-response curve for N-octylguanidine block of sodium channels was not shifted by pyrethroids. The rate at which the pyrethroid-modified sodium channels were blocked by octylguanidine during a depolarizing step depended neither on the concentration of pyrethroids nor on the depolarizing potential, but depended on the concentration of octylguanidine. The time course of the pyrethroid-induced slow sodium tail current was not altered by octylguanidine. We conclude that the actions of pyrethroids and N-octylguanidine on sodium channels are independent of each other.

Animals↗
PubMed1988

Chemical modification of sodium channel inactivation: separate sites for the action of grayanotoxin and tetramethrin.

The gating mechanisms of the sodium channel are known to be modified by grayanotoxin and the pyrethroid tetramethrin. Voltage clamp experiments with internally perfused squid giant axons were performed to determine whether or not these two chemicals shared a common site of action in exerting their effects. An additive effect of the two drugs in prolonging sodium currents was observed. Additionally, the characteristic tetramethrin-induced sodium tail current and the grayanotoxin-induced hyperpolarizing shift in the voltage that activated the sodium current were observed simultaneously and independently of the order of drug introduction. Inactive stereoisomers of tetramethrin, which are known to prevent the active tetramethrin stereoisomers from exerting their effect, had no effect on the development of the grayanotoxin-induced modifications of sodium current. It was concluded that tetramethrin and grayanotoxin act at separate sites of action in modifying the sodium channel gating mechanisms in the squid axon membrane.

Animals↗
PubMed1989

Electrical coupling between secondary hair cells in the statocyst of the squid Alloteuthis subulata.

The cephalopod angular acceleration receptor system has sensory response characteristics similar to those of the vertebrate semicircular canal system and, unusual for an invertebrate, contains secondary receptor hair cells. The experiments reported use intracellular recordings from pairs of hair cells to show that at least one subset of the hair cells is electrically coupled along the entire length of the crista section. The coupling can be reduced by application of heptanol or octanol. Intracellular injection of H+ ions into a hair cell reduces the coupling of cells on the opposite site of the injected hair cell but does not abolish it completely. It is proposed that the coupling is likely to result in an improvement in the signal-to-noise ratio of the receptor system, a reduction in overall frequency response, but an increase in the low frequency sensitivity.

Animals↗
PubMed1990

Brain pathways of the chromatophore system in the squid Lolliguncula brevis.

Brain pathways controlling the chromatophores of the squid Lolliguncula brevis are described using cobalt iontophoresis. The results show several input and output pathways of the anterior and posterior chromatophore and lateral basal lobes. These connections allow coordination and modification of the chromatophore motor program throughout the motor pathway. Unlike other cephalopod species, there seems to be no direct input from the optic lobes to the lateral basal lobes in L. brevis. This species displays only a few simple patterns; therefore the underlying neural pathways for chromatophore control may be different from those of other cephalopods with more extensive patterning repertoires.

Animals↗
PubMed1990

Pyrethroid modifications of the activation and inactivation kinetics of the sodium channels in squid giant axons.

The kinetics of sodium channel activation and inactivation were analyzed in the squid giant axons internally treated with various pyrethroids. Pyrethroids increased the steady-state sodium current in squid giant axons by removing the inactivation. The steady-state sodium conductances in control and pyrethroid-treated axons showed the same voltage dependence, indicating that the removal of inactivation by pyrethroids did not lead to an alteration of gating charge transfer. The pyrethroid-modified sodium channels were activated with a biphasic time course involving the movement of at least two gating particles, and both components were voltage-dependent. The slower component was abolished by treatment with either pronase or N-bromoacetamide. The net elementary charges transported in the electric membrane field were reduced in the course of slow activation of the pyrethroid-induced sodium current. It appears that the 'immobilization' of gating charge is related to the slow activation rather than the inactivation of the sodium channel.

Animals↗
PubMed1990

Classification of presynaptic calcium channels at the squid giant synapse: neither T-, L- nor N-type.

We examined both pharmacological and functional characteristics of the calcium channels which trigger transmitter secretion from giant nerve terminals of squid. These calcium channels are insensitive to organic calcium channel blockers such as dihydropyridines and omega-conotoxin GVIA, moderately sensitive to cadmium, activated by very small depolarizations and slowly inactivating. We conclude that the characteristics of these presynaptic channels do not correspond to the properties of T-, L-, or N-type calcium channels found in other cells.

Animals↗
PubMed1992

Purification of squid synaptic vesicles and characterization of the vesicle-associated proteins synaptobrevin and Rab3A.

Two proteins associated with mammalian synaptic vesicles, the integral membrane protein synaptobrevin and the GTP-binding protein rab3A, are identified in squid nervous tissue using Western blotting and subcellular fractionation of synaptosomes. They both copurify with synaptic vesicles prepared from squid optic lobe. Synaptobrevin (18.1 kDa) is present at high levels in synaptic terminals but at very low levels in axon. Rab3A (27.5 kDa) is a member of the rab family of low-molecular weight GTP-binding proteins which regulates vesicle traffic in secretory and endocytic processes. As resolved with 2-dimensional gels, squid neurons contain at least 16 GTP-binding species (19-29 kDa), and most of these are present in both soluble and particulate fractions. The 24 kDa class of GTP-binding proteins is highly enriched in axonal transport organelles. The characterization of synaptobrevin and rab3A in squid synaptic vesicles extends their known distributions to invertebrates and points to a fundamental importance of these proteins in neurotransmitter release.

Animals↗
PubMed1992

Modulation of nerve membrane sodium channel activation by deltamethrin.

Deltamethrin is a highly potent pyrethroid insecticide that causes hypersensitivity, choreoathetosis, tremors, and paralysis in mammals. It is known to modify the sodium channel in such a way as to prolong the tail current associated with step repolarization following a depolarizing pulse. Using the axial-wire voltage-clamp technique with the giant axon of the squid Loligo pealei, we have demonstrated that deltamethrin also greatly slows the opening of the sodium channel. This was first observed as a decrease, by as much as 80%, in the peak sodium current flowing during a short, 10 ms depolarization. Current flowing through these slowly opening deltamethrin modified sodium channels was observed during the first depolarizing pulse after deltamethrin exposure and developed with a time constant of 320 ms. This supports the idea that deltamethrin can modify sodium channels when they are in the closed or resting state. Further, evidence of this hypothesis was provided by experiments using 0.1 and 10 microM deltamethrin and measuring the tail current amplitude after depolarizing pulses of varying duration (1-1200 ms). The mean time constant for the increase in tail current amplitude was almost concentration independent; 253 ms at 0.1 microM and 193 ms at 10 microM. We conclude that deltamethrin modifies the activation kinetics of sodium channels in such a way as to slow opening and that this modification occurs predominantly when channels are in the closed or resting state.

Animals↗
PubMed1992

Na+ conductance and the threshold for repetitive neuronal firing.

The Hodgkin-Huxley equation for electrogenesis in the voltage clamped squid giant axon was used to predict the effect of altering maximal Na+ conductance (gNa+max) on the repetitive firing process. The main finding was that increasing gNa+max, without changing any other membrane parameter, reduced the threshold current required to evoke repetitive firing. That is, it rendered the membrane hyperexcitable. Threshold for evoking single action potentials was also affected, but much less so. Other consequences of increasing gNa+max were a decrease in the minimum sustainable rhythmic firing frequency (mRFF), a monotonic increase in firing frequency at any given suprathreshold stimulus intensity, an increase in the current value at which intense depolarizing stimuli block rhythmogenesis, an increase in the maximal sustainable firing frequency using intense currents (MRFF), and the consequent expansion of the dynamic range for stimulus encoding. Thus, the control of gNa+max through the regulation of Na+ channel synthesis and membrane incorporation at sites of rhythmogenesis (e.g. axon hillock-initial segment region, or peripheral sensory endings) is a potential regulatory mechanism for neuronal excitability and stimulus encoding.

Action Potentials↗
PubMed1994

The effect of L-glutamate on the afferent resting activity in the cephalopod statocyst.

The effects of bath application of L-glutamate and of excitatory amino acid agonists and antagonists on the resting activity of afferent crista fibers were studied in isolated preparations of the statocyst of the cuttlefish, Sepia officinalis. L-Glutamate (threshold 10(-5) M) and its agonists quisqualate and kainate (thresholds 10(-6) M) increased the resting activity in a dose-dependent manner. Glutamine (threshold 10(-5) M) was also excitatory, while D-glutamate had no effect. Also, no obvious excitatory effects were seen for NMDA and L-aspartate, nor was any antagonistic effect seen for the selective NMDA-receptor antagonist D-2-amino-5-phosphonovaleric acid (D-AP-5). The spider toxin Argiotoxin636 (threshold 10(-11) M), 2-amino-4-phosphonobutyric acid (AP-4), glutamic acid diethyl ester (GDEE), gamma-D-glutamylaminomethyl-sulfonic acid (GAMS), and kynurenic acid decreased the resting activity and effectively blocked or reversed the effect of L-glutamate and its non-NMDA agonists. Preliminary experiments with statocysts from the squid Sepioteuthis lessoniana and the octopod Octopus bimaculoides gave comparable results. All data show that in cephalopod statocysts L-glutamate, via non-NMDA receptors, has an excitatory effect on the activity of afferent fibers, an effect consistent with its possible function as a hair cell transmitter.

Action Potentials↗
PubMed1993

A partial primary structure of squid hepatopancreas organophosphorus acid anhydrolase.

Earlier studies of OPA anhydrolase from the squid, Loligo pealei, report that the enzyme has a molecular weight near 26 kDa, despite the common observation that SDS-PAGE experiments do not support this conclusion. Recent results from protein sequencing and cloning experiments now suggest that the enzyme found in squid hepatopancreas has a molecular weight of about 42 kDa. The enzyme easily degrades into two fragments of 16 kDa and approximately 26 kDa. N-terminal sequence analyses of the intact enzyme and the 16 kDa fragment blotted from an SDS gel and sequenced from the blot have shown conclusively that the intact 42 kDa protein has a blocked N-terminus. Sequence data obtained previously are from the N-terminal portion of the 16 kDa fragment. Additional support for this interpretation has been obtained from PCR analysis of L. pealei mRNA and cDNA. The partial (30 residue) sequence presented here reveals no indication of similarity to any other OPA anhydrolase or aryldialkylphosphatase (EC 3.1.8.1.).

Amino Acid Sequence↗