Ethanol inhibition of L-type Ca2+ channels in PC12 cells: role of permeant ions

Dose-dependent sensorimotor impairment in human ocular tracking after acute low-dose alcohol administration

Key points

Oculomotor behaviours are commonly used to evaluate sensorimotor disruption due to ethanol (EtOH).

The current study demonstrates the dose‐dependent impairment in oculomotor and ocular behaviours across a range of ultra‐low BACs (<0.035%).

Processing of target speed and direction, as well as pursuit eye movements, are significantly impaired at 0.015% BAC, suggesting impaired neural activity within brain regions associated with the visual processing of motion.

Catch‐up saccades during steady visual tracking of the moving target compensate for the reduced vigour of smooth eye movements that occurs with the ingestion of low‐dose alcohol.

Saccade dynamics start to become ‘sluggish’ at as low as 0.035% BAC.

Pupillary light responses appear unaffected at BAC levels up to 0.065%.

Abstract

Changes in oculomotor behaviours are often used as metrics of sensorimotor disruption due to ethanol (EtOH); however, previous studies have focused on deficits at blood‐alcohol concentrations (BACs) above about 0.04%. We investigated the dose dependence of the impairment in oculomotor and ocular behaviours caused by EtOH administration across a range of ultra‐low BACs (≤0.035%). We took repeated measures of oculomotor and ocular performance from sixteen participants, both pre‐ and post‐EtOH administration. To assess the neurological impacts across a wide range of brain areas and pathways, our protocol measured 21 largely independent performance metrics extracted from a range of behavioural responses ranging from ocular tracking of radial step‐ramp stimuli, to eccentric gaze holding, to pupillary responses evoked by light flashes. Our results show significant impairment of pursuit and visual motion processing at 0.015% BAC, reflecting degraded neural processing within extrastriate cortical pathways. However, catch‐up saccades largely compensate for the tracking displacement shortfall caused by low pursuit gain, although there still is significant residual retinal slip and thus degraded dynamic acuity. Furthermore, although saccades are more frequent, their dynamics are more sluggish (i.e. show lower peak velocities) starting at BAC levels as low as 0.035%. Small effects in eccentric gaze holding and no effect in pupillary response dynamics were observed at levels below 0.07%, showing the higher sensitivity of the pursuit response to very low levels of blood alcohol, under the conditions of our study.

Oculomotor behaviours are commonly used to evaluate sensorimotor disruption due to ethanol (EtOH).

The current study demonstrates the dose‐dependent impairment in oculomotor and ocular behaviours across a range of ultra‐low BACs (<0.035%).

Processing of target speed and direction, as well as pursuit eye movements, are significantly impaired at 0.015% BAC, suggesting impaired neural activity within brain regions associated with the visual processing of motion.

Catch‐up saccades during steady visual tracking of the moving target compensate for the reduced vigour of smooth eye movements that occurs with the ingestion of low‐dose alcohol.

Saccade dynamics start to become ‘sluggish’ at as low as 0.035% BAC.

Pupillary light responses appear unaffected at BAC levels up to 0.065%.

Alpha6-containing nicotinic acetylcholine receptor is a highly sensitive target of alcohol

Alcohol use disorder (AUD) is a serious public health problem that results in tremendous social, legal and medical costs to society. Unlike other addictive drugs, there is no specific molecular target for ethanol (EtOH). Here, we report a novel molecular target that mediates EtOH effects at concentrations below those that cause legally-defined inebriation. Using patch-clamp recording of human α6*-nicotinic acetylcholine receptor (α6*-nAChR) function when heterologously expressed in SH-EP1 human epithelial cells, we found that 0.1-5 mM EtOH significantly enhances α6*-nAChR-mediated currents with effects that are dependent on both EtOH and nicotine concentrations. EtOH exposure increased both whole-cell current rising slope and decay constants. This EtOH modulation was selective for α6*-nAChRs since it did not affect α3β4-, α4β2-, or α7-nAChRs. In addition, 5 mM EtOH also increased the frequency and amplitude of dopaminergic neuron transients in mouse brain nucleus accumbens slices, that were blocked by the α6*-nAChR antagonist, α-conotoxin MII, suggesting a role for native α6*-nAChRs in low-dose EtOH effects. Collectively, our data suggest that α6*-nAChRs are sensitive targets mediating low-dose EtOH effects through a positive allosteric mechanism, which provides new insight into mechanisms involved in pharmacologically-relevant alcohol effects contributing to AUD.

Titrating Tipsy Targets: The Neurobiology of Low-Dose Alcohol

Limited attention has been given to our understanding of how the brain responds to low-dose alcohol (ethanol) and what molecular and cellular targets mediate these effects. Even at concentrations lower than 10mM (0.046 g% blood alcohol concentration, BAC), below the legal driving limit in the USA (BAC 0.08 g%), alcohol impacts brain function and behavior. Understanding what molecular and cellular targets mediate the initial effects of alcohol and subsequent neuroplasticity could provide a better understanding of vulnerability or resilience to developing alcohol use disorders. We review here what is known about the neurobiology of low-dose alcohol, provide insights into potential molecular targets, and discuss future directions and challenges in further defining targets of low-dose alcohol at the molecular, cellular, and circuitry levels.

Intracellular calcium plays a critical role in the alcohol-mediated death of cerebellar granule neurons

Alcohol is a potent neuroteratogen that can trigger neuronal death in the developing brain. However, the mechanism underlying this alcohol-induced neuronal death is not fully understood. Utilizing primary cultures of cerebellar granule neurons (CGN), we tested the hypothesis that the alcohol-induced increase in intracellular calcium [Ca(2+)](i) causes the death of CGN. Alcohol induced a dose-dependent (200-800 mg/dL) neuronal death within 24 h. Ratiometric Ca(2+) imaging with Fura-2 revealed that alcohol causes a rapid (1-2 min), dose-dependent increase in [Ca(2+)](i), which persisted for the duration of the experiment (5 or 7 min). The alcohol-induced increase in [Ca(2+)](i) was observed in Ca(2+) -free media, suggesting intracellular Ca(2+) release. Pre-treatment of CGN cultures with an inhibitor (2-APB) of the inositol-triphosphate receptor (IP(3) R), which regulates Ca(2+) release from the endoplasmic reticulum (ER), blocked both the alcohol-induced rise in [Ca(2+)](i) and the neuronal death caused by alcohol. Similarly, pre-treatment with BAPTA/AM, a Ca(2+) -chelator, also inhibited the alcohol-induced surge in [Ca(2+) ](i) and prevented neuronal death. In conclusion, alcohol disrupts [Ca(2+)](i) homeostasis in CGN by releasing Ca(2+) from intracellular stores, resulting in a sustained increase in [Ca(2+)](i). This sustained increase in [Ca(2+)](i) may be a key determinant in the mechanism underlying alcohol-induced neuronal death.

Blood alcohol concentration at 0.06 and 0.10% causes a complex multifaceted deterioration of body movement control

Alcohol-related falls are recognized as a major contributor to the occurrence of traumatic brain injury. The control of upright standing balance is complex and composes of contributions from several partly independent mechanisms such as appropriate information from multiple sensory systems and correct feedback and feed forward movement control. Analysis of multisegmented body movement offers a rarely used option for detecting the fine motor problems associated with alcohol intoxication. The study aims were to investigate whether (1) alcohol intoxication at 0.06 and 0.10% blood alcohol concentration (BAC) affected the body movements under unperturbed and perturbed standing; and (2) alcohol affected the ability for sensorimotor adaptation. Body movements were recorded in 25 participants (13 women and 12 men, mean age 25.1 years) at five locations (ankle, knee, hip, shoulder, and head) during quiet standing and during balance perturbations from pseudorandom pulses of calf muscle vibration over 200s with eyes closed or open. Tests were performed at 0.00, 0.06, and 0.10% BAC. The study revealed several significant findings: (1) an alcohol dose-specific effect; (2) a direction-specific stability decrease from alcohol intoxication; (3) a movement pattern change related to the level of alcohol intoxication during unperturbed standing and perturbed standing; (4) a sensorimotor adaptation deterioration with increased alcohol intoxication; and (5) that vision provided a weaker contribution to postural control during alcohol intoxication. Hence, alcohol intoxication at 0.06 and 0.10% BAC causes a complex multifaceted deterioration of human postural control.

Alcohol intoxication at 0.06 and 0.10% blood alcohol concentration changes segmental body movement coordination

Alcohol intoxication is the cause of many falls requiring emergency care. The control of upright standing balance is complex and comprises contributions from several partly independent mechanisms like coordination, feedback and feedforward control and adaptation. Analysis of the segmental body movement coordination offers one option to detect the severity of balance problems. The study aims were (1) to investigate whether alcohol intoxication at 0.06 and 0.10% blood alcohol concentration (BAC) affected the segmental movement pattern under unperturbed and perturbed standing; (2) whether alcohol affected the ability for movement pattern adaptation; (3) whether one's own subjective feeling of drunkenness correlated to the movement pattern used. Twenty-five participants (13 women and 12 men, mean age 25.1 years) performed tests involving alcohol intoxication. Body movements were recorded at five locations (ankle, knee, hip, shoulder and head) during quiet standing and pseudorandom pulses of calf muscle vibration for 200 s with eyes closed or open. There was no significant effect of alcohol on the general movement pattern in unperturbed stance or on adaptation. However, when balance was repeatedly perturbed, knee movements became significantly less correlated to other body movements over time at 0.10% BAC and when visual information was unavailable, suggesting that the normal movement pattern could not be maintained for a longer period of time while under 0.10% BAC intoxication. Subjective feelings of drunkenness correlated often with a changed upper body movement pattern but less so with changed knee movements. Thus, an inability to relate drunkenness with changed knee movements may be a contributing factor to falls in addition to the direct effect of alcohol intoxication.

Involvement of non-NMDA receptors in the rescue of weaver cerebellar granule neurons and sensitivity to ethanol of cerebellar AMPA receptors in oocytes

The cellular mechanism responsible for the death of cerebellar granule neurons in the weaver mutant mouse is still being intensely investigated. To determine if alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors are involved in producing the weaver phenotype or are altered by the weaver gene, we used (1) reverse transcription and polymerase chain reaction (RT-PCR) to detect transcripts of glutamate receptors (GluR1-4) from wild-type and mutant cerebella; (2) immunocytochemistry to establish the types of glutamate receptors present in granule neurons cultured from normal and homozygous weaver postnatal day 5-6 (P5-6) cerebella; (3) 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a blocker of glutamate (AMPA/Kainate/NMDA) receptors, and 6,7-dinitroquinoxaline-2,3-dione (NBQX), a blocker of AMPA and kainate receptors, to assess the number of neurons and the number of neurons with long neurites in cultures of homozygous weaver granule neurons; (4) two-electrode voltage clamp recordings to study AMPA glutamate receptor expression in Xenopus oocytes after injection of mRNA isolated from cerebella of normal and weaver P5-6, postnatal day 10 (P10) and postnatal day 23 (P23) mice; and (5) ethanol, which at low 1-10 mM concentrations had been shown previously to rescue homozygous weaver granule neurons in culture [Liesi et al., J. Neurosci. Res. 48 (1997) 571-579], to examine its effect on modulation of AMPA receptors expressed from mRNA. By RT-PCR, the mRNA coding for AMPA receptor subunits GluR1-4 were detected from +/+ and wv/wv cerebella, and by immunocytochemistry, GluR1, GluR2/3 and GluR4 were observed to be expressed in cultured +/+ and wv/wv granule cells. CNQX at 10 microM or NBQX at 10 microM significantly increased the number of surviving neurons and the number with long neurites as compared to wv/wv controls. In addition, CNQX was significantly more effective than NBQX. In oocytes injected with mRNA from P10 normal or weaver cerebella, the amplitudes of the responses to kainate were about equal. In contrast, the amplitudes of the kainate-activated currents in oocytes injected with weaver P23 mRNA were about twice as large as the currents observed in oocytes injected with mRNA from normal P23 cerebella, and both were larger than kainate-activated currents observed after injection of P10 normal and weaver mRNA. Kainate-activated AMPA receptor currents in oocytes injected with mRNA from P10 and P23 normal and homozygous weaver cerebella were inhibited by ethanol. There were no significant differences in the inhibition produced by ethanol on currents from P10 or P23 normal and wv/wv mRNA. Thus, P23 weaver cerebellar mRNA expressed more kainate-activated current in oocytes than P23 normal cerebellar mRNA; both normal and weaver cerebellar granule neurons express mRNA coding for functional AMPA receptors that are susceptible to ethanol inhibition.

Acute and chronic effect of alcohol on Ca2+ channels in hepatic stellate cells

BACKGROUND

Hepatic stellate cells have been reported to play important roles in the regulation of hepatic microcirculation via cell contraction. Increase in intracellular calcium concentration is required to induce cell contraction. We have already reported the existence of L-type voltage-operated Ca2+ channels (VOCC), such as smooth muscle cells. On the other hand, alcohol has been known to disturb hepatic microcirculation. In this study, we evaluated the effect of acute and chronic treatment of alcohol on VOCC in rat hepatic stellate cells.

METHODS

Stellate cells isolated from rats were cultured with or without 100 mM ethanol for up to 14 days. VOCC were detected by the patch clamp technique. Cells cultured for 14 days without ethanol were exposed to ethanol to investigate calcium current during membrane depolarization. alpha-Smooth muscle actin (alpha-SMA) was stained by indirect immunofluorescence.

RESULTS

In the control model, VOCC were recognized in cells cultured for more than 7 days. Detection of VOCC increased from 9% on day 7 to 55% on day 14. On the other hand, VOCC in cells treated chronically with 100 mM ethanol appeared earlier than in the control and the incidences were significantly higher than those of the control accompanied with an early activation of cells. In contrast, simultaneous exposure to ethanol during the membrane depolarization inhibited Ca2+ current.

CONCLUSIONS

The expression of Ca2+ channels in stellate cells were up-regulated by the chronic treatment of alcohol accompanied with the transformation to myofibroblast-like phenotype. However, alcohol itself inhibited Ca2+ current.

Effects of ethanol on calcium homeostasis in the nervous system: implications for astrocytes

Ethanol is a major health concern, with neurotoxicity occurring after both in utero exposure and adult alcohol abuse. Despite a large amount of research, the mechanism(s) underlying the neurotoxicity of ethanol remain unknown. One of the cellular aspects that has been investigated in relationship to the neuroteratogenicity and neurotoxicity of ethanol is the maintenance of calcium homeostasis. Studies in neuronal cells and other cells have shown that ethanol can alter intracellular calcium levels and affect voltage and receptor-operated calcium channels, as well as G protein-mediated calcium responses. Despite increasing evidence of the important roles of glial cells in the nervous systems, few studies exist on the potential effects of ethanol on calcium homeostasis in these cells. This brief review discusses a number of reported effects of alcohol on calcium responses that may be relevant to astrocytes' functions.

Neuronal differentiation modifies the effect of ethanol exposure on voltage-dependent calcium channels in NG 108-15 cells

The effect of prolonged (72 h) ethanol (200 mM) exposure on the labeling of L-type (using tritiated PN 200-110) and N-type (using iodinated omega-conotoxin) voltage-dependent calcium channels was investigated in cultured NG 108-15 cells. In undifferentiated cells ethanol produced an 80% increase in PN 200-110 Bmax and no changes in omega-conotoxin binding. Differentiation had a profound effect on the response of cells to ethanol, which in differentiated neuron-like cells decreased omega-conotoxin binding (-53.5%) leaving PN 200-110 labeling of L-type channels unaffected. The effect was time dependent and reversible upon ethanol withdrawal. The decreased omega-conotoxin binding was accompanied by a reduced ability of omega-conotoxin to inhibit K+ -stimulated calcium uptake. The results demonstrate that in cultured NG 108-15 cells ethanol differentially affects DHP and omega-conotoxin-sensitive, voltage-dependent calcium channels and that the effect is also modulated by differentiation of the cell to a neuronal phenotype.