THE EFFECTS OF SEVERAL ALCOHOLS ON THE PROPERTIES OF THE SQUID GIANT AXON

A Review of the Extraction and Closed-Loop Spray Drying-Assisted Micro-Encapsulation of Algal Lutein for Functional Food Delivery

In this study, the physical and chemical properties and bioavailability of lutein have been summarized, with the novelty of this work being the review of lutein from production to extraction, through to preservation and drying, in order to deliver a functional food ingredient. The potential health functions of lutein have been introduced in detail. By comparing algae and marigold flowers, the advantages of algae extraction technology have been discussed. In this article, we have introduced the use of closed-loop spray drying technology to microencapsulate lutein to improve its stability and solubility. Microencapsulation of unstable substances by spray drying is a potentially useful direction that is worth exploring further.

[Therapeutic strategies for oromandibular dystonia]

Oromandibular dystonia is characterized by tonic or clonic involuntary spasms of the masticatory, lingual and / or muscles in the stomatognathic system. It is often misdiagnosed as craniomandibular dysfunction or psychiatric disease. According to clinical features, the oromandibular dystonia is classified into 6 subtypes (jaw closing-, jaw opening-, tongue-, jaw deviation-, jaw protrusion-, and lip dystonia). There are several treatment methods like botulinum toxin injection, muscle afferent block (injection of lidocaine and alcohol into the masticatory or tongue muscles for blocking muscle afferents from muscle spindle), occlusal splint, and oral surgery (coronoidotomy). Most of patients can be treated successfully according to subtype by combination of these treatments. Special treatment recommendations for each subtype were described in this focus article. Accurate diagnosis and treatment of oral dystonia requires comprehensive knowledge and skills of both oral and maxillofacial surgery and neurology. Therefore, collaboration among these departments is very important.

Dantrolene blockade of ryanodine receptor impairs ethanol-induced behavioral stimulation, ethanol intake and loss of righting reflex

Calcium has been characterized as one of the most ubiquitous, universal and versatile intracellular signals. Among other substances with the ability to alter intracellular calcium levels, ethanol has been described as particularly relevant because of its social and economic impact. Ethanol effects on calcium distribution and flux in vitro have been widely studied, showing that acute ethanol administration can modulate intracellular calcium concentrations in a dose dependent manner. Intracellular calcium released from the endoplasmic reticulum plays a determinant role in several cellular processes. In this study, we aim to assess the effect of dantrolene, a ryanodine receptor antagonist, on three different ethanol-elicited behaviors: locomotor activity, loss of righting reflex and ethanol intake. Mice were challenged with an injection of dantrolene (0-5 mg/kg, i.p.) 30 min before ethanol (0-4 g/kg, i.p.) administration. Animals were immediately placed in an open field cylinder to monitor distance travelled horizontally or in a V-shaped trough to measure righting reflex recovery time. For ethanol intake, dantrolene (0-5mg/kg, i.p.) was administered 30 min before ethanol (20%, v/v) exposure, following a drinking in the dark paradigm. Our results showed that dantrolene selectively reduces ethanol-induced stimulation, loss of righting reflex, and ethanol intake in a dose dependent manner. Together, these data suggest that intracellular calcium released from the endoplasmic reticulum may play a critical role in behavioral effects caused by ethanol, and point to a calcium-dependent pathway as a possible cellular mechanism of action for ethanol.

Participation of L-type calcium channels in ethanol-induced behavioral stimulation and motor incoordination: effects of diltiazem and verapamil

Calcium flux through voltage gate calcium channels (VGCC) is involved in many neuronal processes such as membrane depolarization, gene expression, hormone secretion, and neurotransmitter release. Several studies have shown that either acute or chronic exposure to ethanol modifies calcium influx through high voltage activated channels. Of special relevance is the L-type VGCC. Pharmacological manipulation of L-type calcium channels affects ethanol intake, ethanol discrimination and manifestations of withdrawal syndrome. The present study investigates the role of L-type channels on the psychomotor effects (stimulation and sedation/ataxia) of ethanol by testing the effects of different L-type calcium channel blockers (CCB) on such behaviors. Mice were pretreated intraperitoneally with the CCB, diltiazem (0-40 mg/kg) or verapamil (0-30 mg/kg) 30 min before ethanol (0-3.5 g/kg). Locomotion was measured in an open field chamber for 20 min immediately after ethanol. The two CCB tested prevented locomotor stimulation, but not locomotor suppression produced by ethanol. Doses of the two CCB which reduced ethanol stimulation, did not alter spontaneous locomotion. The ataxic effects of ethanol (1.25 g/kg), measured with an accelerating rotarod task, were not affected by diltiazem (20mg/kg) or verapamil (15 mg/kg). In addition, our results indicated that ethanol is more sensitive to the antagonism of L-type calcium channels than other drugs with stimulant properties; doses of the two CCB that reduced ethanol stimulation did not reduce the psychomotor effects of amphetamine, caffeine or cocaine. In conclusion, these data provide further evidence of the important involvement of L-type calcium channels in the behavioral effects produced by ethanol.

Regulation of sodium channel function by bilayer elasticity: the importance of hydrophobic coupling. Effects of Micelle-forming amphiphiles and cholesterol

Membrane proteins are regulated by the lipid bilayer composition. Specific lipid–protein interactions rarely are involved, which suggests that the regulation is due to changes in some general bilayer property (or properties). The hydrophobic coupling between a membrane-spanning protein and the surrounding bilayer means that protein conformational changes may be associated with a reversible, local bilayer deformation. Lipid bilayers are elastic bodies, and the energetic cost of the bilayer deformation contributes to the total energetic cost of the protein conformational change. The energetics and kinetics of the protein conformational changes therefore will be regulated by the bilayer elasticity, which is determined by the lipid composition. This hydrophobic coupling mechanism has been studied extensively in gramicidin channels, where the channel–bilayer hydrophobic interactions link a “conformational” change (the monomer↔dimer transition) to an elastic bilayer deformation. Gramicidin channels thus are regulated by the lipid bilayer elastic properties (thickness, monolayer equilibrium curvature, and compression and bending moduli). To investigate whether this hydrophobic coupling mechanism could be a general mechanism regulating membrane protein function, we examined whether voltage-dependent skeletal-muscle sodium channels, expressed in HEK293 cells, are regulated by bilayer elasticity, as monitored using gramicidin A (gA) channels. Nonphysiological amphiphiles (β-octyl-glucoside, Genapol X-100, Triton X-100, and reduced Triton X-100) that make lipid bilayers less “stiff”, as measured using gA channels, shift the voltage dependence of sodium channel inactivation toward more hyperpolarized potentials. At low amphiphile concentration, the magnitude of the shift is linearly correlated to the change in gA channel lifetime. Cholesterol-depletion, which also reduces bilayer stiffness, causes a similar shift in sodium channel inactivation. These results provide strong support for the notion that bilayer–protein hydrophobic coupling allows the bilayer elastic properties to regulate membrane protein function.

[Muscle afferent block in the treatment of oromandibular dystonia. Difference in effect between masticatory and lingual muscles]

Oromandibular dystonia is a neuromuscular disorder characterized by tonic or clonic involuntary spasms of the masticatory and lingual muscles. We treated 50 patients with this movement disorder by injection of lidocaine and alcohol into the masticatory or tongue muscles to block muscle afferents from muscle spindle. The patients were divided according to clinical features into four groups: jaw-closing, jaw-opening, jaw-deviation, and tongue dystonias. Objective evaluation of the symptoms before and after therapy was based on a clinical scaling protocol in terms of four parameters (mastication, speech, pain, and discomfort scales). Symptoms improved in all patients without major side effects. The overall objective improvement (60.2+/-29.5%) was significantly (P<0.005, ANOVA) lower in tongue dystonia (14.1%) than in jaw-closing dystonia (67.6%) and jaw-opening dystonia (68.3%). Although the response of the muscle afferent block to tongue dystonia was hardly satisfactory, this treatment is suggested to be effective for oromandibular dystonia.

Factors influencing the therapeutic effect of muscle afferent block for oromandibular dystonia and dyskinesia: implications for their distinct pathophysiology

Oromandibular dystonia (OMD) is a focal dystonia manifested by involuntary masticatory and/or lingual muscle contractions. Muscle afferent block (MAB) by injecting anaesthetic and alcohol intramuscularly is recently used for the treatment of OMD. To study the factors affecting the efficacy of MAB, 44 patients with OMD were treated by local injection of lidocaine and ethanol. They were divided into four groups (spastic, rhythmic, dyskinetic, and task-specific) according to the pattern of incisal movement and involuntary contraction. We used a clinical scaling protocol in terms of four parameters (mastication, speech, pain, and discomfort) to evaluate the change of symptoms objectively. The relationship of improvement in clinical scores with various parameters was assessed statistically. The overall objective improvement was 60.2 +/- 29.5%. The scores decreased significantly (P<0.0001, paired t-test) after MAB. The maximal incisal velocity significantly correlated inversely with the clinical improvement, and MAB was particularly effective for spastic contraction. Dyskinetic and rhythmic groups showed variable and significantly less improvements than the spastic group. MAB is highly effective for OMD, but not for the patients with dyskinetic symptoms. The jaw movement pattern is an important factor for predicting the outcome. The difference in the response to MAB in OMD and oral and/or orofacial dyskinesia suggests the distinct pathophysiology between the two.

Customized EMG needle insertion guide for the muscle afferent block of jaw-deviation and jaw-opening dystonias

OBJECTIVE

Jaw-opening and jaw-deviation dystonias are characterized by mouth opening or lateral shift of the mandible due to involuntary contraction of the lateral pterygoid muscle, causing difficulties in speech or mastication. We introduce the method of muscle afferent block by using a removable device for inserting a hollow electromyographic needle.

STUDY DESIGN

A technique for fabricating a customized needle insertion guide into the lateral pterygoid muscle is described. Using the device, intramuscular injection of lidocaine and ethanol was performed in 3 patients with jaw-opening dystonia and 2 with jaw-deviation dystonia. Subjective improvement was assessed on a linear self-rating scale ranging from 0 (no improvement) to 100 points (complete cure).

RESULTS

The overall subjective improvement was 72% +/- 16.4% without major side effects.

CONCLUSIONS

The device is very useful for safe and accurate injection into the lateral pterygoid muscle. The muscle afferent block is effective for jaw-opening and jaw-deviation dystonias.

Neuronal nicotinic acetylcholine receptors: a new target site of ethanol

Whereas a variety of neuroreceptors and ion channels have been demonstrated to be affected by ethanol including GABAA receptors, NMDA receptors, non-NMDA glutamate receptors, 5-HT3 receptors and voltage-gated calcium channels, neuronal nicotinic acetylcholine receptors (nnAChRs) have recently emerged as a new target site of ethanol. The nnAChRs are different from the muscle type nicotinic AChRs with respect to their molecular architecture and pharmacology. This article briefly reviews the structure, distribution and function of nnAChRs for which a considerable amount of information has been rapidly accumulated during the past 5-10 years. The potent and unique action of ethanol on nnAChRs has been unveiled only during the past few years. Most recent developments along this line of ethanol action are discussed in this paper.

Muscle afferent block for the treatment of oromandibular dystonia

Oromandibular dystonia is a focal dystonia involving the masticatory and tongue muscles, causing difficulties in speech or mastication. We treated 13 patients with this condition by injecting diluted lidocaine and alcohol intramuscularly. This method is aimed at reducing muscle spindle afferent activity. The symptoms had been resistant to other therapies such as pharmacotherapy or dental treatment. All patients showed clinical improvement after this therapy with reduced EMG activities in the affected muscles, whereas control injection of normal saline gave no changes in EMG activities. The overall subjective improvement was 57.7 +/- 25.1% (mean +/- standard deviation) in a self-rating scale. The mean response of the jaw elevator muscles (70 +/- 13.1%) was significantly higher (p < 0.02, t test) than that of the depressor muscles (38 +/- 28.4%). Despite the precise mechanism being unknown, this difference might be related to the smaller number of muscle spindles in the depressor than the elevator muscles. This therapy is useful for the treatment of drug-resistant oromandibular dystonia.

ANOMALOUS RECTIFICATION IN THE SQUID GIANT AXON INJECTED WITH TETRAETHYLAMMONIUM CHLORIDE

The injection of tetraethylammonium chloride into the giant axon of the squid prolongs the action potential and eliminates most of the late current under voltage-clamp. Experiments on fibers in an external medium of high potassium ion concentration demonstrate that injected tetraethylammonium chloride causes rectification of the instantaneous current-voltage curve for potassium by excluding outward current. This interference with the flow of outward potassium ion current underlies the prolongation of the action potential seen in tetraethylammonium-injected fibers.

Tonic vibration reflex and muscle afferent block in writer's cramp

Patients with focal dystonia take advantage of certain cutaneous or proprioceptive sensory inputs to alleviate their symptoms ("sensory trick"). We examined the effects of increasing muscle spindle activity by the tonic vibration reflex maneuver and decreasing it by intramuscular injection of lidocaine. The vibration was applied to the palm or the tendon of forearm muscles in 15 patients with writer's cramp and 15 age-matched normal subjects. In 11 patients, the vibration induced dystonic postures or movements typical of those seen during writing. Normal subjects showed either no response to the vibration or a gradually developing tonic vibration reflex only in the wrist and finger flexors, which produced visible movements with a significantly longer latency (12.5 +/- 6.7 seconds [mean +/- standard deviation]) than what was observed in the patients (2.7 +/- 2.5 seconds, p < 0.0001). Local injection of lidocaine (0.5%, 5-40 ml/muscle) attenuated the tendon reflex with relatively little effect on the M response. Injection into muscles with increased activity produced marked reduction of dystonic movements and significant clinical improvement in 13 patients, whereas injection into the other muscles had no effect. The clinical benefit lasted for 1 to 24 hours after injection. In 13 patients who had additional injections of 10% ethanol, which blocks sodium channels for a longer period than does lidocaine, the duration of action was prolonged to 5 to 21 days. These findings suggest that muscles causing dystonic movements have abnormal sensitivities to vibration at rest and that muscle afferents may play a pivotal role in producing dystonic movements.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetic analysis of the denaturation process by alcohols of sodium channels in squid giant axon

1. The effects of several aliphatic alcohols on sodium currents were examined in the intracellularly perfused squid giant axon when the same concentration of alcohol was applied on both sides of the membrane. 2. An irreversible suppression of sodium currents, accompanied by anaesthesia at high alcohol concentration, was examined in detail using four aliphatic alcohols, that is, ethanol, 1-propanol, 1-butanol and 1-pentanol. 3. This irreversible effect seemed to be attributable to the sequential denaturation of sodium channels, because the kinetics, the current-voltage relation and the sodium channel activation-voltage curve did not change after the sodium current decreased. 4. The time course of the remaining sodium conductance was measured as a function of the sum of the alcohol application time by repeating the process of applying and completely washing out alcohol. The remaining sodium conductance decayed as a function of time in a single exponential manner. This decay time constant depended strongly on the concentration of alcohol and could be assumed to be the denaturation time constant of the sodium channel. 5. The denaturation time constant decreased as the alcohol concentration increased. This time constant is proportional to the Nth power of the alcohol concentration. The N values are 4.3, 4.5, 5.8 and 7.6 for ethanol, 1-propanol, 1-butanol and 1-pentanol, respectively. This implies that alcohol molecules bind to a restricted number of specific sites in the sodium channel protein to cause the denaturation. 6. The concentration of alcohol which caused the same amount of denaturation is related to the exponential function of the carbon number of the alcohol. Considering the partition coefficient of alcohol between lipid and aqueous solution, the concentration of alcohol in the membrane which denatured half of the sodium channels in 2 h can be calculated to be 0.5 M for all alcohols.

The effect of aliphatic alcohols on the transient potassium current in hippocampal neurones

1. The transient potassium current was recorded in single hippocampal CA1 neurones from the rat by use of the whole-cell patch clamp technique. The effects on this current of a homologous series of aliphatic alcohols, ranging from butanol to octanol, were investigated. 2. The predominant effect of octanol (and the other alcohols) was to cause an increase in the initial rate of decay of the transient potassium current together with a slight decrease in the rate of decay of later phases of the current, such that the current decay became markedly non-monotonic. The alcohols also caused a decrease in peak current amplitude which could not be accounted for solely by the change in current decay kinetics. 3. The effect of the alcohols was concentration-dependent and readily reversible. Increasing chain length increased the potency of each alcohol by about 3 fold for each methylene group added. Other than a difference in potency, there appeared to be little difference in the action of aliphatic alcohols of different chain length on the transient current. 4. The alcohols did not appreciably change the voltage-dependence of steady state inactivation or activation of the transient potassium current. 5. The rate of inactivation of the transient current in these cells was only weakly voltage-dependent. This weak voltage-dependence was not changed by the presence of aliphatic alcohols, neither was the effect of the alcohols themselves voltage-dependent. 6. The potencies of each of the aliphatic alcohols were well correlated with their respective membrane/buffer partition coefficients, a finding which implies a hydrophobic locus of action.

Effects of n-alkanols and a methyl ester on a transient potassium (IA) current in identified neurones from Helix aspersa

1. A two-microelectrode voltage clamp was used to determine the effects of n-butanol, n-hexanol, n-octanol, n-decanol and methyl hexanoate on a transient potassium (IA) current in identified Helix aspersa neurones. Experiments were carried out at a temperature of 10-12 degrees C. 2. Each n-alkanol reversibly reduced the amplitude of the IA current. Logarithmic dose-response curves for the current reduction by each homologue were sigmoidal and had slope factors of around four. The concentrations required to reduce the peak (with time) current at -30 mV by 50% (ED50 +/- fitted standard error) were: 57 +/- 5 mM (n-butanol); 2.0 +/- 0.1 mM (n-hexanol); 0.28 +/- 0.02 mM (n-octanol) and 0.016 +/- 0.001 mM (n-decanol). Methyl hexanoate also reduced the current amplitude, with an ED50 of 1-2 mM. The Helix IA current thus showed a similar sensitivity to n-alkanols to that of squid and rat sodium currents but was rather more sensitive than the squid delayed rectifier potassium current. 3. The n-alkanol ED50 concentrations were used to calculate a standard free energy per methylene group for adsorption to a site of action in the cell of -3.1 +/- 0.2 kJ/mol. This suggested a hydrophobic site or sites of action. The regularity of the change in free energy with chain length was maintained up to, and including, n-decanol. This implied that the site(s) could accommodate a ten-carbon chain as readily as an eight-carbon chain. 4. The voltage dependencies of IA current activation and steady-state inactivation were not consistently altered by treatment with n-alkanols at concentrations around or above their current suppression ED50 concentrations. 5. The kinetics of current activation and inactivation were affected, particularly by lower chain length compounds. At 60 mM n-butanol reduced the time constant for development of inactivation of open channels (tau b) by 56%, while 0.016 mM n-decanol produced only a 13% reduction. n-Butanol (60 mM) also caused a substantial (76%) reduction in the time constant for development of inactivation in channels which were presumed to be closed. The effects of n-alkanols on the current time-to-peak (tc) were complex, showing both increases and decreases, but these actions also declined with chain length. Methyl hexanoate (1 mM) reduced tau b by around 30% and tc by around 20%. 6. n-Alkanols have now been shown to inhibit a number of voltage-gated ion conductances.(ABSTRACT TRUNCATED AT 400 WORDS)

Ethanol decreases the velocity of spike propagation along a fast motor axon

Intracellular recordings were made from the fast bender excitor motor axon in autotomized crab limbs bathed in normal saline, and in salines made with up to 240 mM of ethanol. The presence of ethanol reduced the amplitude, the rise time and the decay time of the evoked action potential, and decreased the velocity at which the spike was conducted down the axon. There was a linear relationship between each of these four parameters and the concentration of ethanol in the saline. The close relationship between spike rise time and conduction velocity suggests that ethanol slows the rate of membrane depolarization by the spike and thus decreases the velocity at which action potentials are propagated along the axon.

Differential effects of alcohols on the spike threshold of an identified motor axon in a crab (Pachygrapsus crassipes)

Observations were made on the fast bender excitor (FBE) axon in autotomized crab limbs bathed in salines made up with different alcohols. It has been shown previously that the presence of ethanol at a certain level causes a single action potential to generate additional spikes in the peripheral axon branches. The present study examines the level of different alcohols required to induce peripheral spike generation. For primary alcohols, increasing the molecular weight decreased the level of alcohol required to produce peripheral spike generation. The threshold level of 2-butanol was greater than 1-butanol, but less than tertiary-butanol. These results are explained in terms of the partition coefficient, so that an alcohol with a higher partition coefficient enters the lipid bilayer more readily, thus a lower threshold level of that alcohol is required in the saline to generate additional spikes.

Block of sodium current by heptanol in voltage-clamped canine cardiac Purkinje cells

Heptanol blocks sodium current (INa) in nerve, but its effects on cardiac INa have not been well characterized. Block of INa by heptanol was studied in 16 internally perfused voltage-clamped cardiac Purkinje cells at reduced Na+ (45 mM outside, 0 mM inside). Heptanol block of peak sodium conductance was well described by a single-site binding curve with half block at 1.3 mM (20 degrees C) and showed no "use dependence." With 1.5 mM heptanol, block increased slightly by 0.7%/degrees C from 10 degrees C to 27 degrees C. With 3.0 mM heptanol, steady-state availability shifted by 9.4 +/- 1.3 mV (n = 6) in the hyperpolarizing direction, and steady-state activation shifted by 8.3 +/- 2.2 mV (n = 5) in the depolarizing direction, thus closing off the INa "window current." Heptanol also decreased the time to peak and accelerated the decay of INa. Similar results were found with octanol at lower concentrations. These alcohols have important effects on cardiac INa at concentrations used in studies for cellular uncoupling in heart.

The response of single cardiac sodium channels in neonatal rats to the dihydropyridines CGP 28392 and (-)-Bay K 8644

Cell-attached patch clamp recording of elementary Na+ currents were performed at 19 degrees C in neonatal cultured rat heart cells to study Na+ channel properties in the presence of dihydropyridines. Bath application of racemic CGP 28392, at 5 mumol/l, activated Na+ channels. By increasing the open probability, P0, and/or the number of functioning Na+ channels, peak INa in reconstructed macroscopic Na+ currents rose without changes in the decay kinetics. This was accompanied by a prolongation of open time. (-)-Bay K 8644 (1-10 mumol/l) had the same effect. In the presence of either agonist, Na+ channels retained an uniform open state and, as estimated from the mean number of openings per sequence, their initial tendency to reopen. Rarely appearing ultralong opening sequences are unlikely to be drug-induced as Na+ channels can likewise switch into this particular activity mode under drug-free conditions. Racemic CGP 28392, at 50 mumol/l, blocked Na+ channels in an all-or-none fashion suggesting that one enantiomer acts as agonist and the other enantiomer as blocker. A quite different response consisting of the occurrence of a second open state with a several-fold increased life time and a significantly increased reopening was observed with (-)-Bay K 8644 in damaged cardiocytes with hyperpermeable membranes and after patch excision into drug-containing solution. Evidence was obtained from control inside-out patches that this increased reopening is most probably caused by the solvent, ethanol.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of inactivation in the effects of n-alkanols on the sodium current of cultured rat sensory neurones

1. The whole-cell patch-clamp technique has been used to investigate the actions of n-butanol, n-pentanol, n-hexanol and n-octanol on the sodium current of cells isolated from the dorsal root ganglia (DRGs) of neonatal rats and maintained in short-term tissue culture. 2. The influence of n-alkanols on the level of steady-state inactivation of the sodium current was investigated by a standard two-pulse protocol. All alkanols increased the level of resting inactivation and this was manifested as a hyperpolarizing shift of the relationship between the steady-state inactivation parameter (h infinity) and membrane potential. The mid-point of the h infinity curve was moved by up to -30 mV. 3. The relationship between the shift in the mid-point of the inactivation curve (delta Vh) and aqueous n-alkanol concentration has been derived for each n-alkanol. These are complex in shape and do not appear consistent with a hypothesis that the increase in inactivation results from 1:1 binding of an alkanol molecule to a single site on the channel protein. 4. The aqueous concentrations used ranged from 70 mM-n-butanol to 0.05 mM-n-octanol. However, equal fractional saturations of n-alkanols produced approximately equal shifts in the h infinity curve, particularly in the range 0.01-0.07 saturated. This implies a hydrophobic site of action, with a standard free energy per methylene group for adsorption to the site from the aqueous phase of ca -3.2 kJ/mol. 5. The increase in resting inactivation was not the sole means by which n-alkanols reduced the sodium current. The current was still reduced in cells pre-pulsed to sufficiently negative potentials to remove steady-state inactivation even in the presence of alkanols. The concentration required to reduce the current by 50% (ED50) has been interpolated for each n-alkanol. From these data it was estimated that the standard free energy per methylene group for adsorption to the site of action was ca -3.1 kJ/mol, similar to that calculated for the effect on inactivation. The concentration dependence of this residual block indicated the involvement of more than one n-alkanol molecule. 6. The n-alkanols increase the level of inactivation of rat DRG cell sodium channels at potentials around the resting membrane potential and this effect contributes to their local anaesthetic action.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of homologous series of anaesthetics on a resting potassium conductance of the squid giant axon

The effects of n-alkanes (n-pentane to n-octane), n-alkanols (n-pentanol to n-undecanol) and two carboxylic esters (methyl pentanoate and methyl octanoate) on the conductance of squid giant axons in a high potassium, zero sodium bathing solution have been examined. Sodium and delayed rectifier potassium channels were as far as possible pharmacologically blocked. A substantial fraction of the measured conductance is attributed to a recently-described, voltage-independent, potassium channel. Anaesthetics block this channel but its sensitivity is markedly different from those of other squid axon ion channels.

The interaction of homologous series of alkanols with sodium channels in nerve membrane vesicles

The potency of members of the homologous series of alkanols to block 22Na uptake through sodium channels stimulated by veratridine was studied in membrane vesicles obtained from lobster walking leg nerves. A cut-off was revealed at the level of 1-undecanol. However, secondary isomers of inactive primary homologues, such as 5-dodecanol and 5-tridecanol, were able to block ion flux. From the concentration required for an equipotent effect, it was calculated that the standard free energy for adsorption of primary alkanols is -725 cal/mol CH2. Furthermore, since the concentration required for an equipotent effect for primary isomer was found to be lower than that obtained for secondary isomers, it is concluded that the latter are less potent than the former. The similarity between this set of results and those obtained in intact frog sciatic nerve (J. Requena et al., J. Membrane Biol., 84:229-238, 1985) offers further support to the notion that the procedure employed to isolate the membrane vesicles does preserve the Na channels. However, the mechanism of alcohol inhibition of the Na channel in isolated membrane vesicles would seem to be somewhat different from that preferred in axons. While in vesicles the block needs to be thought in terms of a reduction in the number of conducting Na channel, in axons this is considered to be the less likely mode of action, mainly because under veratridine it is not possible to invoke a shift in the steady-state activation or inactivation.

Alkanol effects on early potassium currents in Aplysia neurons depend on chain length

The relationship between alkanol chain length and effects on the transient potassium current, IA, were examined in three identified Aplysia californica neurons with ethanol (EtOH), butanol (BuOH), and hexanol (HxOH). Qualitative differences were found when the actions of EtOH were compared with those of the longer-chain-length alcohols. Whereas EtOH primarily affected the decay time constant of IA, having minimal effects on amplitude, BuOH and HxOH exerted their major effect on the amplitude of IA, reducing it, while their effects on decay kinetics were much less pronounced. The effects of EtOH on IA decay are cell specific among identified neurons of the Aplysia nervous system. The actions of BuOH and HxOH did not mimic these interneuronal differences. These data, coupled with data previously reported by us and others, make it unlikely that EtOH exerts its actions on IA via perturbation of a bulk lipid phase within the membrane.

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.

Local anesthetic action of carboxylic esters: evidence for the significance of molecular volume and for the number of sites involved

The effects of the homologous series of carboxylic esters, methyl propionate to methyl decanoate, on the steady-state inactivation of the sodium current in squid axons have been studied. The esters moved the relationship between the inactivation parameter, h infinity, and the membrane potential in the hyperpolarizing direction, thus reducing the number of sodium channels available at the resting potential. The concentration dependence of the shift at the mid-point of the curve of h infinity against potential has been measured for all esters except decanoate, which was almost inactive. Two aspects of these concentration dependences suggest that molecular volume is an important determinant of the effectiveness of each ester. Firstly, there is a sharp decline in activity above methyl hexanoate. This cut-off in activity resembles that for hydrocarbons where it has been suggested [e.g., Haydon, D.A., Urban, B.W. 1983, J. Physiol. (London) 341:411-427] to a result from a decrease in uptake with increasing molecular volume. (Further data for the hydrocarbons n-butane to n-heptane are reported here.) Secondly, the smallest compounds, methyl propionate and methyl butyrate, are less effective than would be predicted if equal membrane concentrations of each ester produced the same shift. The aqueous concentration dependences for these esters indicate that below methyl hexanoate, as the series is descended, progressively higher membrane concentrations are required to produce a given shift. This would be expected if the volume of ester in the membrane, rather than the number of molecules, is important.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of N-alcohols on potassium conductance in squid giant axons

The effect of bath application of several short chain N-alcohols on voltage-dependent potassium conductance has been studied in intact giant axons of Loligo forbesi under voltage-clamp conditions. All tested alcohols (methanol, ethanol, propanol, butanol, heptanol and octanol) were found to depress potassium conductance only at concentrations much larger than those necessary to reduce sodium conductance. The efficacy of the different molecules was correlated with the carbon-chain length. In all cases the effects were found to be at least partly reversible. Low concentrations of propanol (100 mM) or heptanol (1 mM) were found to increase potassium conductance whereas higher concentrations had the usual depressing effect. The two alcohols were found to induce a slow inactivation of the potassium conductance. A detailed analysis of the time course of the turning-on of the potassium current for various pulse potentials in the presence of TTX revealed that, for membrane potential values more positive than -20 mV, the time constant of activation was reduced in the presence of propanol or heptanol. The delay which separates the change in potential and the turning-on of the potassium current, which was systematically analysed for different pulse and prepulse potential values, was increased by the two alcohols, the curve relating this delay to prepulse potential being shifted towards larger (positive) delays. This high degree of complexity in the effects on potassium conductance suggests that the alcohol molecules modify several more or less independent mechanisms associated with the turning-on of the potassium current.

The electrophysiology of potassium channels

Ethanol actions have mainly been described in terms of physicochemical membrane actions. More recently, investigators using intracellular electrophysiological recording techniques have been able to describe ethanol effects on ionic channel function. This chapter reviews the literature on ethanol-potassium channel interactions and discusses the hypothesis that the inhibitory effects of ethanol on central neurons are mediated by increased potassium conductance.

Effects of ethanol on the functional properties of sodium channels in brain synaptosomes

Voltage-sensitive sodium channels in excitable cell membranes are responsible for the rapid increase in permeability to sodium ions that occurs during depolarization. Neurotoxins that bind with high affinity and specificity to voltage-sensitive sodium channels have been widely used to identify and characterize the structure and function of sodium channels in nerve and skeletal muscle. This chapter describes the actions of ethanol on the functional properties of voltage-sensitive sodium channels in mammalian brain nerve endings. The effects of acute and chronic ethanol administration are also reviewed. Alterations in the function of neuronal membrane sodium channels may be involved in the depressant effect of ethanol.

The effects of ethanol on the electrophysiology of calcium channels

Acute ethanol intoxication affects many systems in the body, especially the central nervous system. Because early experiments using axonal preparations required very high concentrations of ethanol to produce ionic current alterations, researchers turned their attention away from specific effects on electrogenesis and looked for effects at the synapse. The role of Ca2+ in the release of neurotransmitters was well known and was considered a possible site of action for ethanol. Indeed, several studies demonstrated that ethanol alters Ca2+ binding or transport in synaptosomes and neural tissue. The purpose of this chapter is to present electrophysiological evidence for the acute effects of ethanol on calcium channels. It is necessary first to define the relevant ethanol concentrations and to describe the characteristics of tissue preparations that may best help to determine the effects of ethanol. A discussion of these two points along with a brief synopsis of the role of Ca2+ in excitable tissues is presented. This is followed by a discussion of the effects of ethanol on Ca2+ and Ca2+-activated conductances in both nonmammalian and mammalian cells, and a model is presented in an attempt to unify the experimental evidence of the acute effects of ethanol.

Control of cytoplasmic calcium with photolabile tetracarboxylate 2-nitrobenzhydrol chelators

This paper introduces nitr-2, a new Ca2+ chelator designed to release Ca2+ upon illumination with near UV (300-400 nm) light. Before illumination nitr-2 has Ca2+ dissociation constants of 160 and 630 nM in 0.1 and 0.3 M ionic strength respectively; after photoconversion to a nitrosobenzophenone the values shift to 7 and 18 microM, high enough to liberate substantial amounts of Ca2+ under intracellular conditions. The speed of release is limited by a dark reaction with rate constant 5 s-1. Aplysia central neurons injected with nitr-2 and exposed to UV light exhibit two separate Ca2+-dependent membrane currents: one carried by potassium ions and one a nonspecific cation current. A quantitative estimate of the spatial distribution of intracellular [Ca2+] changes in large cells filled with a high concentration of nitr-2 and exposed to an intense UV flash is offered.

Ethanol effects on voltage-dependent membrane conductances: comparative sensitivity of channel populations in Aplysia neurons

The study of ethanol (EtOH) action is interesting because of its clinical relevance and for the insights it provides into structure-function relationships of excitable membranes. This paper describes the concentration dependencies of various parameters of four currents in Aplysia cells. ICa is the most sensitive of the currents studied. There was a significant reduction of ICa at concentrations of 50 mM EtOH. At low concentrations, the reduction of amplitude was the primary effect of ethanol, with the kinetics and voltage dependency of activation not affected. INa and IA were also affected, but at EtOH levels higher than those which altered ICa. The primary effect of EtOH on INa was a reduction in its amplitude, although the time to peak current flow was increased by EtOH. The effects of EtOH on IA were cell specific and, for the purposes of this paper, we examined the giant metacerebral cell (MCC). In MCC, the primary effect of EtOH on IA was an increase in the time course of inactivation. The time to peak IA was also increased by high concentrations of EtOH, but its amplitude was unaffected even at high concentrations. The delayed rectifier current, IK, was the most EtOH resistant of the currents examined. High EtOH concentrations augmented the amplitude of IK, although even at 600 mM concentrations, the percentage change was only 30%. Our results indicate that the calcium channel is very susceptible to the influence of ethanol and is a serious candidate to be the primary target of EtOH action in the nervous system. The differential sensitivity of voltage-dependent currents and individual components of a given current suggests further experiments to probe the relationship between membrane structure and channel function in excitable membranes.

Effects of n-alkanols on the calcium current of intracellularly perfused neurons of Helix aspersa

The effects of n-alkanols on the calcium current (ICa) were studied in molluscan neurons perfused intracellularly and voltage clamped using a suction pipette technique. All n-alkanols employed in this experiment (methanol, ethanol and butanol) decreased the peak amplitude of ICa and caused acceleration of the decay of ICa in a dose-dependent manner at all membrane potentials. The concentrations of n-alkanols required for these actions decreased as the hydrocarbon chain increased in length. The results suggest that these effects on the ICa of molluscan neurons may be related to the lipophilic properties of n-alkanols.

The actions of some general anaesthetics on the potassium current of the squid giant axon

A number of small organic molecules with general anaesthetic action have been examined for their effects on the voltage-dependent potassium current of the squid giant axon. They include representatives of the three classes of anaesthetics examined in previous studies on the sodium current (Haydon & Urban, 1983a, b, c), i.e. the non-polar molecules n-pentane, cyclopentane and CCl4, several n-alkanols and the inhalation anaesthetics chloroform, halothane, diethyl ether and methoxyflurane. Potassium currents under voltage clamp were recorded in intact and in intracellularly perfused axons before, during and after exposure to the test substances, and the records were fitted with equations similar to those proposed by Hodgkin & Huxley (1952). Shifts in the curves of the steady-state activation against membrane potential and reductions in the potassium conductance at 60 or 70 mV membrane potential have been tabulated. On the same intact axons, all the anaesthetics with the exception of methoxyflurane reduced potassium currents less than sodium currents by about a factor of two or more. For the n-alkanols, butanol to decanol, the concentrations required to reduce the potassium current at 60 mV membrane potential by 50% were determined. For n-butanol to n-heptanol, the standard free energy per CH2 for adsorption to the site of action was estimated to be -2.91 kJ mol-1 as compared with -3.04 kJ mol-1 for reduction of the sodium current. The magnitude of the free energy decreased for alkanols with longer chain lengths. At anaesthetic concentrations that reduce the sodium current by 50%, the hydrophobic substances n-pentane and cyclopentane reduced the maximal sodium conductance, gNa, and the potassium conductance at 70 mV, gK70, equally by about a third, while the n-alkanols reduced both parameters by less than 10%. By contrast, diethyl ether and methoxyflurane were more effective in reducing the maximal potassium conductance. All of the test substances examined, except n-pentane and n-hexane, shifted the voltage dependence of the potassium steady-state activation in the depolarizing direction. A broad qualitative correlation was found between the shifts in the activation curves for sodium and potassium currents but, quantitatively, the agreement between the two shifts was poor. In n-decanol and methoxyflurane solutions, the voltage-clamped potassium currents exhibited pronounced inactivation-like behaviour. These currents can be fitted by the Hodgkin-Huxley formalism if an inactivation term analogous to the sodium current inactivation is added.(ABSTRACT TRUNCATED AT 400 WORDS)

Blocking and modifying actions of octanol on Na channels in frog myelinated nerve

The actions of externally applied n-octanol on Na channels in myelinated frog nerve fibres were studied under voltage clamp conditions. Upon octanol application peak Na inward currents declined in two phases: 90% of the reduction occurred in less than 2 min but a steady-state was reached only after 15 min. During washout the currents came to a stable level within 10 min. The reduction of Na inward currents by octanol was dependent on the amplitude and duration of prepotentials. At the resting potential (VH = 0 mV) 0.4 mM octanol reduced peak Na inward currents at V = 60 mV by 50%. After a prepulse of -60 mV and 50 ms duration Na currents decreased only by 20%. At a hyperpolarizing holding potential of VH = -28 mV 0.7 mM octanol reduced peak inward Na currents to one half. Octanol depressed Na currents at all potentials by approximately the same factor. The Na reversal potential VNa remained unchanged. 0.7 mM external octanol shifted the Na activation curve m infinity (V) by 5 mV to more positive and the inactivation curve h infinity (V) by 14 mV to more negative potentials. The midpoint slopes of both curves were reduced. The time constants of Na activation and inactivation at small depolarizations were decreased. The conductance gamma of a single Na channel and the number No of conducting Na channels per node were determined from nonstationary Na current fluctuations. 0.7 mM octanol increased gamma by a factor of 1.6 and reduced No by a factor of 0.34. It is concluded that octanol blocks some Na channels and modifies the remaining unblocked channels.

Effect of ethanol on subthreshold currents of Aplysia pacemaker neurons

The subthreshold currents in bursting pacemaker neurons of the Aplysia abdominal ganglion were individually studied with the voltage clamp technique for sensitivity to 4% ethanol. The most prevalent effect of ethanol on unclamped bursting neurons was a hyperpolarization. This was shown to be due to a decrease of a voltage independent inward leakage current. Direct measurement of the Na-dependent slow inward current showed that this current was eliminated by 4% ethanol. Direct measurement of the Ca-dependent slow inward current showed that this current was substantially reduced by 4% ethanol. Injection of EGTA into cell bodies did not eliminate the ethanol-induced block of the slow inward calcium current. Thus, ethanol cannot be reducing the Ca-dependent slow inward current solely by an increase of internal calcium concentration. The effect of ethanol on voltage dependent outward current was measured by blockage of all inward current. The peak outward current was increased by ethanol. The rate of inactivation of this outward current was also increased. Calcium activated potassium current (IK(Ca)) is particularly complicated in its response to ethanol because it is dependent on both Ca and voltage for its activation. The level of IK(Ca) elicited in response to constant Ca injection was increased by ethanol treatment. The level of this current as activated by voltage clamp pulses was either increased or decreased depending on the neuron type. Ca2+ activated potassium conductance increased e-fold for a 26 mV depolarization in membrane holding potential. Ethanol decreased this voltage dependence to e-fold for a 55 mV change in potential. This result was interpreted to mean that ethanol shifted an effective Ca2+ binding site of these channels from about halfway through the membrane field to one quarter of the way across. The same theoretical approach allowed the further conclusion that ethanol caused an increased internal free calcium concentration probably by decreasing calcium binding by intracellular buffers.

Membrane disordering by anesthetic drugs: relationship to synaptosomal sodium and calcium fluxes

The effects of membrane perturbants (ethanol, pentobarbital, chloroform, diethylether, phenytoin, cis-vaccenic acid methylester, and cis-vaccenoyl alcohol) on the lipid order of mouse brain synaptic plasma membranes (SPM) were tested by fluorescence polarization using 1,6-diphenyl-1,3,5-hexatriene (DPH) as a probe of the membrane core and 1-[4-(trimethylammonium)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH) as a probe of the membrane surface. The compounds decreased the fluorescence polarization of both probes, indicating that they disordered the membrane lipids. The decrease in polarization was, however, greater for DPH than for TMA-DPH, suggesting a greater effect on the membrane core than on the membrane surface. The voltage-dependent uptake of 24Na and 45Ca was studied in isolated mouse brain synaptosomes as a measure of membrane function. All of the compounds inhibited sodium influx, and their potencies for decreasing sodium uptake and fluorescence polarization of DPH were linearly correlated (r = 0.91). The relationship between changes in sodium influx and TMA-DPH polarization was less consistent (r = 0.66). Synaptosomal calcium uptake was inhibited by most, but not all, of the perturbants, but this inhibition was poorly correlated with changes in fluorescence polarization of DPH (r = 0.36) or TMA-DPH (r = 0.26). These results indicate that the function of synaptic sodium channels is correlated with lipid order in the hydrophobic core of the membrane and that the inhibitory effects of intoxicant-anesthetic drugs on neuronal sodium fluxes may be the result of their capacity to disorder these lipids. In contrast, the effects of drugs on voltage-dependent calcium channels were not clearly related to the capacity of these agents to disorder membrane lipids.

General anaesthetics: effects on transmitter release

In this report, the physiological effects, observations and events leading to transmitter release in both central nervous system and peripheral synapses are discussed. The presynaptic modulation of transmission at the central nervous system and at the neuromuscular junction was investigated using electrophysiological and neurochemical techniques. It was concluded that various general anaesthetics may affect the presynaptic mechanism of transmission, but these effects were controversial. For example, terminal excitability, which is taken as an index for presynaptic activity, could either be reduced or increased by general anaesthetics. Similar conflicting effects have been reported for the action of general anaesthetics on spontaneous and evoked release of ACh, uptake and release of intracellular Ca2+, and choline transport into the presynaptic nerve terminals.

The effects of valinomycin on ion movements across the sarcoplasmic reticulum in frog muscle

The effects of valinomycin on the elemental composition and the fractional volume of the terminal cisternae (t.c.) of the sarcoplasmic reticulum (s.r.) were determined in rapidly frozen frog semitendinosus muscles. The concentrations of valinomycin used for the electron probe studies (5 microM) had no effect on tetanus tension or t.c. volume (2.% of fibre volume). Mitochondria were markedly swollen and their K content was significantly increased in both the resting and the tetanized valinomycin-treated muscles. Valinomycin had no effect on the concentration of Na, Mg, P, Cl, K and Ca in the t.c. of resting muscles. In untreated, tetanized muscles, Ca2+ release was accompanied by the uptake of K and Mg into the t.c. in an amount that was significantly less than the positive charge removed through Ca2+ release, confirming previous observations showing an apparent charge deficit (Somlyo, Gonzalez-Serratos, Shuman, McClellan & Somlyo, 1981). Valinomycin abolished the apparent charge deficit: in tetanized, valinomycin-treated muscles, the uptake of K into the t.c. was significantly (P less than 0.001) greater than in the untreated muscles and Mg uptake also remained highly significant. It is suggested that Ca2+ release from activated muscle is an electrogenic process and that the K+ conductance of the s.r. in untreated frog muscles is insufficient to allow charge neutralization of the Ca2+ current during release. The increase in K+ permeability caused by valinomycin permits the greater counter movement of K+ under the combined influence of the electrical potential generated by outward Ca2+ movement and the acidic cation binding proteins in the lumen of the s.r. The results are consistent with the proposal (Somlyo et al. 1981) that in normal frog muscles not treated with valinomycin, the apparent positive charge deficit observed after a tetanus reflects the movement of protons and, possibly, organic cations.

Postsynaptic actions of ethanol and methanol in crayfish neuromuscular junctions

Actions of ethanol and methanol on excitatory postsynaptic channels activated by quisqualate were investigated in opener muscles from the first walking leg and the claw of crayfish. Both ethanol and methanol reduced the elementary currents [i] that flow through channels operated by quisqualate in a concentration-dependent manner but did not affect the apparent mean open time, tau noise, of the channels estimated from power spectra. 0.26 mol/l ethanol, or 1 mol/l methanol, respectively, reduced [i] e-fold. Ethanol also markedly decreased the size and the decay time constant tau (sEPSCs) of spontaneous excitatory postsynaptic currents (sEPSCs). At ten fibres, on the average, 0.26 mol/l ethanol decreased tau (sEPSCs) by a factor 1.56 +/- 0.24 (SD). tau (sIPSCs) and tau noise of inhibitory postsynaptic currents apparently were not affected by ethanol. Moreover the size of elementary inhibitory postsynaptic currents did not decrease in the presence of this alcohol. Thus, in crayfish opener muscles ethanol seems to selectively depress excitatory postsynaptic currents.

Nitrogen narcosis and pressure reversal of anesthetic effects in node of Ranvier

To compare sodium channel block by hyperbaric nitrogen with that induced by other anesthetics and to examine the basis for pressure antagonism to anesthetic condition block, voltage clamped nodes of Ranvier were exposed to nitrogen at pressures at 1-14 atm alone and in combination with helium to a total pressure of up to 100 atm. At 7 and 14 atm nitrogen, sodium currents were reversibly depressed without accompanying changes in the current-voltage relation. The curve relating steady-state inactivation (h infinity) to voltage was shifted in the hyperpolarizing direction, as is the case with other general anesthetic agents. The time constant of inactivation (tau h) was slightly decreased at depolarized potentials. The preceding companion paper demonstrated an opposite effect of hyperbaric helium on the properties of sodium inactivation. Addition of helium pressure in the presence of nitrogen at 14 atm did not increase peak sodium current with inactivation maximally removed, but it did shift the h infinity curve back toward control levels, thus increasing sodium current at points on the slope of the curve. It is proposed that these opposing shifts in steady-state inactivation levels are the basis for pressure antagonism to anesthetic conduction block. In the case of inert gases and volatile anesthetic agents, the antagonism may be direct but has not been shown to be so. In the case of the local anesthetic benzocaine, differences in the voltage dependence of anesthetic and pressure-induced changes in tau h indicate the antagonism is indirect.