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PubMedDate not supplied

Tricaine (MS-222): effects on ionic conductances of squid axon membranes.

Experiments utilizing internally perfused squid giant axons have been carried out to determine the mode of action of tricaine (MS-222) in producing its anesthetic effects. Tricaine, in concentrations of 1 and 3 mM, was applied to the internal surface of the membrane via the perfusion system. Peak sodium current and steady-state potassium current were measured by the axial-wire voltage clamp technique. Tricaine suppressed both of these membrane ionic currents with the major effect being on the peak sodium current. Its action on nerve membrane appeared quite similar to other local anesthetics. One major difference was noted in that tricaine shifts sodium conductance curves in the direction of depolarization along the potential axis, an effect quite similar to that observed with increasing external Ca2+ concentration and with application of pentobarbital.

Aminobenzoates↗
PubMed1975

Comparison of the action of different barbiturates on squid axon membranes.

Experiments utilizing squid giant axons have been carried out to determine if the duration of anesthesia obtained from phenobarbital, pentobarbital and hexobarbital can be explained by events related to their action at the nerve membrane level. For comparison, the barbiturates were perfused both outside and inside the squid axon at concentrations which produced an approximately equivalent depression of the maximum rate of rise of the action potential. The time to 50% maximum block and the time to 50% maximum recovery following washing, were compared for all three drugs. All three barbiturates were more potent from inside the squid axon than from the outside. This finding coupled with the fact that the time course of the drug effects was much shorter when applied inside as compared to outside suggests an internal site of action. There was no statistically significant difference between a short acting barbiturate and a long acting barbiturate with respect to their time course of action or recovery when they were both applied to either the inside or outside of the membrane.

Action Potentials↗
PubMed1976

The effects of holothurin A on the resting membrane potential and conductance of squid axon.

The effects of a marine toxin, holothurin A, on the electrical properties of squid axon membranes were studied. External application of holothurin A to the intact axon produced an irreversible depolarization of the membrane to nearly zero potential. Internal perfusion of squid axon with holothurin A produced a biphasic depolarization of the membrane. The time course of the depolarization was much shorter with internal application than with external application. The holothurin A-induced depolarization was partially reversed either by reduction of the external sodium concentration to 1 mM or by removal of sodium from both external and internal solutions. The results demonstrate an increase in resting sodium permeability as one of the mechanisms underlying the depolarization by holothurin A. However, external application of tetrodotoxin had no effect on the membrane depolarization. Increase of the resting permeability to potassium is suggested as the additional mechanism of depolarization. A model is developed which predicts this anomalous depolarization.

Animals↗
PubMed1988

Dynamic instability of native microtubules from squid axons is rare and independent of gliding and vesicle transport.

Dynamic instability characterizes the steady-state behavior of microtubules in vitro whereby polymer mass remains constant, while individual microtubules in the population may either grow or shrink. Video-enhanced contrast light microscopy was used to directly observe dynamic length changes in native, MAP-containing microtubules from squid axoplasm. We wanted to determine whether dynamic instability characterizes the steady-state behavior of axoplasmic microtubules in vitro. The lengths of a representative population of over 400 microtubules were analyzed. "Dynamic" microtubules were found to represent about 2% of the population. This observation is different from that described for cultured cells or microtubules assembled from PC-purified tubulin where most microtubules were either growing or shrinking.

Animals↗
PubMed1985

Lipid fluidity of the outer segment membranes from cephalopod retina.

Membranes from the retina outer segments of squid (Loligo sp.) were isolated by sucrose continuous gradient. In these membranes, phosphatidylcholine and phosphatidylethanolamine were shown to be the most abundant lipids, while rhodopsin was the predominant protein. Steady-state fluorescence depolarization of the probe 1,6 diphenyl-1,3,5-hexatriene was employed to characterize the microviscosity of the photosensitive membranes and of the vesicles prepared from their lipid extract. The lipid fluidity parameter (r0/r-1)-1 in these membranes ranged between approximately 3.8 and approximately 0.95 (0-38 degrees C), while the value of the lipid extract vesicles ranged between approximately 3 and approximately 0.6. No phase transition was observed in the membrane and vesicle preparation in the range of temperatures under study [0-38 degrees C). Photosensitive membranes from cuttlefish (sepia officinalis) gave similar results. The (r0/r-1)-1 value in this species varied between approximately 4 and approximately 1.2 (0-38 degrees C) with a linear dependence on temperature. In these outer segments the bleaching of rhodopsin did not cause any change of the membrane lipid fluidity value. The present results are compared with those obtained in bovine rod outer segments.

Animals↗