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At least 577 records · Page 32Linked to original sources
PubMed1990

Determination of intracellular buffer values after metabolic inhibition by fluoride and nitrilotriacetic acid.

Non-bicarbonate buffer values have been analysed in homogenates of squid mantle muscle and toad gastrocnemius muscle using the PCO2 equilibration technique. Homogenate metabolism was inhibited by the addition of potassium fluoride and nitrilotriacetic acid. After an initial change in the concentration of organic phosphates a new metabolic equilibrium was achieved which was insensitive to pH changes during PCO2 variations. Inaccurate measurements of homogenate buffer values could, thereby, be prevented. The accumulation of inorganic phosphate during the initial metabolic shift caused an increase in homogenate buffer values. Levels of unbound inorganic phosphate, which are effective in buffering, were estimated by enzymatic analysis in homogenate ultrafiltrates. Based on the evaluation of apparent dissociation constants pK', and buffer values for fluoride and inorganic phosphate, the non-bicarbonate, non-phosphatei (i: inorganic) buffer value of the tissue was calculated. The level of free inorganic phosphate in the resting tissue was considered for an estimate of the intracellular non-bicarbonate buffer value under control conditions.

Adenosine Diphosphate↗
PubMed1975

The histology and fine structure of the olfactory organ of the squid Lolliguncula brevis Blainville.

The olfactory organ of the squid has a thick, pseudostratified epithelium containing five morphological types of ciliated receptors. In the simplest receptors the cilia originate separately in the distal pole of the cell. All other receptors have some type of cilia filled cavity, varying from a simple pocket of cilia at the surface to a completely closed vesicle filled with cilia in cells deep in the epithelium. The receptors are compared to cells in the rhinophore of Nautilus and the olfactory organs of coleoid cephalopods. Possible functions of the olfactory organ, based on its morphology, are discussed.

Animals↗
PubMed1975

A light and electron microscope study of intra-epithelial putative mechanoreceptors in squid suckers.

Putative mechanoreceptor neurons in the cuticularized epithelium of the suckers of the squid Lolliguncula brevis, were investigated using light and electron microscope techniques. These neurons were found to have a multipolar shape, thick unbranched axon, glial cell ensheathment, and accessory nerve fiber innervation. The need for electrophysiological and/or behavioral studies on these putative mechanoreceptors is emphasized.

Animals↗
PubMed1977

The squid accessory nidamental gland: ultrastructure and association with bacteria.

The structure of the accessory nidamental gland of the female squid, Loligo pealei, has been investigated using transmission and scanning electron microscopy. The accessory gland has many of the structural features of a secretory organ. The basic structural unit is a tubule composed of a single layer of epithelial cells containing ordered arrays of rough endoplasmic reticulum and a lumenal surface covered with microvilli, cilia, and structural specialization presumed to be involved in secretion. The lumen of each tubule is filled with a dense population of bacteria. During sexual maturation of the squid, the accessory gland changes in color from white to mottled red. The accessory gland of the sexually mature squid has a mixture of red, white, and yellow tubules; in each case, the color of the tubule is due to the bacterial population occupying the tubule. Since the red color of the gland is due to the pigmentation of the bacteria, the bacteria must be responsive to the sexual state of the host, possible through a change in the nature of the material secreted into the tubule lumen. The bacteria can be cultured easily. but in culture they fail to synthesize the red pigment.

Animals↗
PubMed1987

Activity of tralomethrin to modify the nerve membrane sodium channel.

Deltamethrin is a potent type II pyrethroid insecticide which can modify sodium channel gating kinetics in nerve membranes. The actions of another type II pyrethroid tralomethrin to modify sodium channel kinetics have been ascribed to deltamethrin, to which tralomethrin is known to be converted under certain experimental conditions. The objective of this study was to determine if tralomethrin was intrinsically active in modifying the nerve membrane sodium channel, the major target site of pyrethroids. Experiments were performed using the squid giant axon under voltage-clamp conditions. In axons treated with either pyrethroid, a large sodium tail current was generated upon repolarization from a depolarized level and decayed slowly with a dual exponential time course. The fast time constant for tralomethrin was 165 +/- 110 msec and the slow time constant was 3793 +/- 802 msec. For deltamethrin the time constants were significantly shorter, the fast time constant being 34 +/- 6 msec and the slow time constant being 835 +/- 282 msec. The cumulative dose-response relation of tralomethrin revealed two binding sites with apparent dissociation constants of 0.06 and 5 microM. Deltamethrin appeared to bind to only one site with an apparent dissociation constant of 0.25 microM. It is clear that there are large differences in the gating kinetics of the sodium channels modified by tralomethrin and deltamethrin which are incompatible with the idea that tralomethrin is active only after conversion to deltamethrin. The differences in sodium channel gating kinetics after modification by tralomethrin versus deltamethrin indicate that tralomethrin is intrinsically active in modifying the nerve membrane sodium channels.

Animals↗
PubMed1982

Actions of nortetrodotoxin on frog muscle and squid axon.

Nortetrodotoxin, prepared by oxidation of the C6 end of tetrodotoxin, probably exists in solution as an equilibrium mixture of a hemilactal and a lactone form of a hydrated ketone of C6. On both frog muscle fibers under constant-current conditions and squid giant axon under voltage-clamped conditions, nortetrodotoxin selectively blocks the sodium channel. On frog muscle fibers, the solution of nortetrodotoxin used, which was several months old, was 1/13 as active as tetrodotoxin. On the squid giant axon, a freshly prepared solution of nortetrodotoxin was about 1/4 as active. These observations indicate that nortetrodotoxin possesses a substantial degree of biological activity. The suitability of nortetrodotoxin as an intermediate for synthesizing derivatives of tetrodotoxin is discussed.

Animals↗
PubMed1985

Actions of 4-epitetrodotoxin and anhydrotetrodotoxin on the squid axon.

The actions of the newly discovered 4-epitetrodotoxin and of anhydrotetrodotoxin have been studied on the internally perfused squid giant axon under voltage-clamped conditions. Both compounds are selective in blocking only the sodium channel. The concentration for reducing the sodium current to one-half is 13.2 nM for 4-epitetrodotoxin and 298 nM for anhydrotetrodotoxin. Compared with tetrodotoxin, the relative potencies are 0.39 for 4-epitetrodotoxin and 0.018 for anhydrotetrodotoxin. The results suggest that hydrogen bonding at C-4 and C-9 is an important contributing force in binding to the membrane receptor site.

Animals↗
PubMed1985

Actions of Ptychodiscus brevis toxins on nerve and muscle membranes.

Pharmacological actions of two brevetoxins isolated from Ptychodiscus brevis, T17 and T34, on nerve and muscle membranes were studied using vertebrate and invertebrate preparations. T17 (10 ng/ml) caused an increase in the frequency of miniature endplate potentials (MEPPs) in rat and frog neuromuscular junctions. Application of tetrodotoxin (TTX) completely abolished the increase in MEPP frequency. The results suggest that T17 depolarizes the nerve terminal through opening of the sodium channel. Application of either T17 or T34 to the crayfish and squid giant axons caused a dose-dependent depolarization of the axon membranes with a maximum depolarization of about 30 mV. The depolarizing action was antagonized by sodium-free external saline solution or TTX. Voltage clamp experiments demonstrated that the primary action of the toxins is to cause the sodium channels to open at the normal resting potential. The binding of toxin to a channel site could be prevented by procaine, but not by TTX. The binding site for T17 is presumably separate from the TTX receptor, but related or identical to the binding site for procaine. The brevetoxin-induced depolarization of the nerve terminal membrane with the subsequent enhanced transmitter release is the underlying mechanism for a number of pharmacological actions on various neuro-effector systems.

Animals↗
PubMed1985

Actions of epimers of 12-(OH)-reduced saxitoxin and of 11-(OSO3)-saxitoxin on squid axon.

The actions of the 12 alpha-saxitoxinol, 12 beta-saxitoxinol and a C-12 ethylene thioketal derivative of saxitoxin, as well as those of 11 alpha-(OSO3)-saxitoxin, 11 beta-(OSO3)-saxitoxin and 11 alpha-(OH)-saxitoxin, have been examined on the isolated squid giant axon. Each of these analogues acted similarly to saxitoxin in blocking specifically the sodium channel. The relative potencies are: STX (1); 11 beta-(OSO3)-STX (gonyautoxin III) (0.42); 11 alpha-(OSO3)-STX (gonyautoxin II) (0.20); 11 alpha-(OH)-STX (0.10); 12 alpha-saxitoxinol (0.0021); 12 beta-saxitoxinol (0.0005). Thus, the presence of a bulky and negatively charged sulphate group on C-11 does not materially affect the biological activity of STX. Hydrogen bonding at the C-12 position is probably an important means of binding of STX to the membrane receptor site. The difference between the epimers of saxitoxinol suggests that the H in one of them may be geometrically better aligned than that in the other, with the hydrogen acceptor group in the receptor.

Amphibian Proteins↗
PubMed1986

Effects of intra- and extracellularly applied phospholipases C on excitability of squid giant axons.

The effects of phospholipases C on the membrane excitability of the squid giant axon were investigated using phosphatidylcholine-hydrolyzing phospholipase C and sphingomyelinase C of Bacillus cereus, and phosphatidylinositol-specific phospholipase C of Bacillus thuringiensis. When the squid axon was perfused internally with phosphatidylcholine-hydrolyzing phospholipase C in KF or K-glutamate solution, the action potential was blocked in 4-7 min and membrane resistance decreased with time to a level less than one-tenth that of control. These effects were irreversible. When the axon was perfused internally with sphingomyelinase C in KF solution, the action potential was decreased to 30% in 3 min. Perfusion with enzyme-free KF solution fully restored the action potential. When the axon was perfused internally with phosphatidylinositol-specific phospholipase C in K - glutamate solution, the action potential was gradually decreased and blocked after 10 min. Perfusion with enzyme-free KF solution restored the action potential by 70%. When phosphatidylcholine-hydrolyzing phospholipase C was applied externally to the squid axon, the action potential and the membrane resistance were slowly but irreversibly decreased. These results suggest that membrane phospholipids, such as phosphatidylcholine and phosphatidylinositol, may be associated with the excitability of the membrane of the squid axon.

Action Potentials↗
PubMed1986

The pH dependence of the tetrodotoxin-blockade of the sodium channel and implications for toxin binding.

On the internally perfused, voltage-clamped squid giant axon, the effect of pH on the potency of tetrodotoxin in blocking the sodium current has been re-examined at pH 7.8 and 8.8. Confirming previous studies, tetrodotoxin is weaker at pH 8.8, when the deprotonated C-10 -OH makes the toxin molecule a zwitterion. In contrast to previous studies, our results, based on full dose--response relations, show that the relative potency at the two pH values appreciably exceeds the ratio of the abundance of the protonated C-10 form. In a medium of lowered ionic strength, tetrodotoxin is weaker, and the relative potency at pH 7.8 and 8.8 approaches the ratio of the relative abundance of the C-10 -OH. The results are believed to support hydrogen bonding at C-10 as a contributing factor in the binding of tetrodotoxin to the membrane receptor.

Animals↗
PubMed1993

Toxicology of a bovine paraplegic syndrome.

A clinical entity named 'bovine paraplegic syndrome' ('síndrome parapléjico de los bovinos') has spread alarmingly in the cattle-growing areas of the central and eastern plains of Venezuela. It is estimated that four million cattle are bred in the area where the disease occurs. The mortality ranges from 5 to 25% of the animals at risk, mostly pregnant or lactating cows. The principal characteristic of the bovine paraplegic syndrome is ventral or sternal decubitus, in animals that make vain efforts to stand when stimulated. The diagnosis is established when all other possible causes (e.g. paralytic rabies, botulism and blood parasites such as Anaplasma marginal, Babesia bovis, B. bigemina, and Trypanosoma vivax) have been ruled out clinically and by laboratory tests. Death always occurs, usually after a few days, and there is no known treatment. In this work, we describe results that show the presence of a toxin in the cattle suffering from, or liable to suffer from the syndrome. The toxin is produced by ruminal bacteria. In squid giant axons under voltage clamp conditions, the toxin blocks the sodium current. We detected the toxin analytically by absorbance measurements at 340 nm after reacting with picrylsulfonic acid. We obtained a good separation of the toxin with isocratic high pressure liquid chromatography, using 40% methanol in water on phenylborasil columns.

Animals↗
PubMed1994

Specific blockage of squid axon resting potassium permeability by Haliclona viridis (Porifera: Haliclonidae) toxin (HvTX).

The action of partially purified HvTX, toxin of the marine sponge H. viridis, was explored on the giant axon of the tropical squids Doryteuthis plei and Sepioteuthis sepioidea. HvTX depolarizes the nerves dose dependently. The effect occurs after blocking sodium channels with tetrodoxin (1 microM), removing external Na+, blocking electrically excitable K+ channels with 3,4-diaminopyridine (10 mM) or internal and external application of tetraethylammonium (40 mM). Ouabain (up to 10 mM) does not modify HvTX effect. The action of HvTX occurs only when it is applied to the outer phase of the nerve membrane; microinjection of the toxin into the axons lacks depolarizing effects. HvTX reduces the dependence of membrane potential on external potassium concentration. The apparent 86Rb+ permeability (pi') was measured in axons of S. sepioidea. The value of pi' in normal artificial sea water was 80 (61,96) nm/sec (median and its 95% confidence interval, n = 8) and raised to 1030 (588, 2113) nm/sec (n = 7) when the axons were depolarized to 0 mV raising external K+ to 300 mM. In axons depolarized with HvTX (10 mM external K+) to 0 mV, pi' was 88 (55, 97) nm/sec (n = 8). HvTX could not prevent (P >> 0.05) the increase in pi' induced by 300 mM K+ when the ion concentration was raised before toxin application [pi' = 660 (354, 1876) nm/sec, n = 7]. Most of the 86Rb+ permeability increase in high K+ was prevented if HvTX was added before external K+ was raised [pi' = 298 (264, 337) nm/sec, n = 8]. All the measures of pi' were carried out in solutions containing 1 microM tetrodotoxin, 1 mM 3,4-diaminopyridine and 2 mM ouabain.

Animals↗