Post-traumatic amnesia: a scoping review & content analysis of behavioral disturbances

OBJECTIVE

The aim of this scoping review was to identify behavioral disturbances exhibited by patients in post-traumatic amnesia (PTA). While behavioral disturbances are common in PTA, research into their presentation and standardized measures for their assessment are limited.

DESIGN

The study protocol was registered with PROSPERO (CRD42021268275). A scoping review of databases was performed according to pre-determined criteria on 29 July 2021 and updated on 13 July 2022. A conventional content analysis was used to examine and categorize behavioral disturbances.

RESULTS

Thirty papers met the inclusion criteria, of which 27 reported observations and/or scores obtained on behavioral scales, and 3 on clinician interviews and surveys. None focused exclusively on children. Agitation was the most frequently assessed behavior, and Agitated Behavior Scale was the most used instrument. Content analysis, however, bore eight broad behavioral categories: disinhibition, agitation, aggression, lability, lethargy/low mood, perceptual disturbances/psychotic symptoms, personality change and sleep disturbances.

CONCLUSION

Our study revealed that while standardized assessments of behavior of patients in PTA are often limited to agitation, clinical descriptions include a range of behavioral disturbances. Our study highlights a significant gap in the systematic assessment of a wide range of behavioral disturbances observed in PTA.

Predictive validity of the Westmead Post-Traumatic Amnesia Scale for functional outcomes in school-aged children who sustained traumatic brain injury

The Westmead Post-Traumatic Amnesia Scale (WPTAS) is routinely used for the assessment of post-traumatic amnesia (PTA) in children who sustained traumatic brain injury (TBI). Yet, the WPTAS' predictive validity for functional outcomes is largely unknown. We aimed to determine whether PTA duration measured by the WPTAS (i) differentially predicts functional outcomes and (ii) contributes to predictions of outcomes beyond the Glasgow Coma Scale (GCS) in children who sustained TBI. Participants were children and adolescents with moderate-to-severe TBI (n = 55) aged 8-15 years. PTA duration was assessed with the WPTAS. Outcomes at the first outpatient follow-up were scored on the Kings Outcome Scale for Childhood Head Injury (KOSCHI) and the TBI Outcome Domain Scale-Extended (ODS-E). Longer PTA and lower GCS were both significantly correlated with worse (i) global outcomes: presence of disability on the KOSCHI and lower score on the ODS-E and (ii) select specific outcomes on the ODS-E: mobility, mood and cognition. PTA duration predicted cognitive outcome on the ODS-E independently, beyond GCS. Together, PTA duration and GCS, predicted the global KOSCHI outcome, as well as the ODS-E mobility and mood outcomes. Neither GCS nor PTA duration correlated with the ODS-E communication, impulsivity/disinhibition, headache, fatigue, sensory impairments or somatic complaints outcomes. PTA duration measured by the WPTAS is a significant unique predictor of functional cognitive outcomes in children who sustained moderate-to-severe TBI, and in combination with the GCS, a significant predictor of global, and several specific functional outcomes.

Convergent validity of the child behavior checklist sleep items in children with moderate to severe traumatic brain injury

AIM

The Child Behavior Checklist (CBCL) includes several sleep items. We aimed to examine the convergent validity of CBCL sleep scores with validated sleep measures, and to explore their functional correlates.

METHODS

This cross-sectional study included 44 children with moderate to severe TBI, aged 6-15 years. Parents completed the CBCL and Sleep Disturbance Scale for Children (SDSC), and children wore actigraphy watches.

RESULTS

We found significant, albeit differential, associations between CBCL and SDSC sleep scores. Specifically: (i) "trouble sleeping" with SDSC total score, (ii) "trouble sleeping" and "nightmares" with SDSC initiating and maintaining sleep, (iii) "talks/walks in sleep" with SDSC arousal, and (iv) "overtired," "sleeps more" and CBCL sleep composite with SDSC excessive somnolence. The CBCL item "sleeps less" was the only significant predictor of functioning; children who slept less had lower social competence. No associations were found between CBCL sleep scores and actigraphy.

CONCLUSIONS

The CBCL does not provide a comprehensive assessment of sleep disturbances in children with moderate to severe TBI. Nevertheless, certain CBCL sleep items demonstrate initial convergent validity with subscales of the SDSC assessing select types of sleep disturbances. The CBCL may be useful in research and clinical situations when administration of more comprehensive assessment sleep tools is not viable.

Behavioral interventions for sleep disturbances in children with neurological and neurodevelopmental disorders: a systematic review and meta-analysis of randomized controlled trials

STUDY OBJECTIVES

Sleep disturbances are common and associated with negative functional and health consequences in children with neurological and neurodevelopmental disorders (NNDDs) and represent an important potential target for behavioral interventions. This systematic review examined the efficacy of behavioral sleep interventions (BSIs) for children with NNDDs and comorbid sleep disturbances.

METHODS

A systematic search of MEDLINE, EMBASE, PsychINFO, and CENTRAL was conducted in April 2019. Randomized controlled trials (RCTs) of BSI for children with NNDDS were included. Meta-analysis and GRADE quality ratings were performed on sleep and secondary functional outcomes (cognition, academics, and behavior).

RESULTS

Nine RCTs were identified (n = 690; Mage = 8.39 ± 2.64years; 71.11% male). The quality of the evidence was predominantly rated as moderate. Posttreatment improvements in sleep were found on self-reported sleep disturbances (total sleep disturbance [standardized mean difference, i.e. SMD = 0.89], night wakings [SMD = 0.52], bedtime resistance [SMD = 0.53], parasomnias [SMD = 0.34], sleep anxiety [SMD = 0.50]) and self-reported sleep patterns (sleep duration [SMD = 0.30], sleep onset duration [SMD = 0.75]) and (2) objectively measured actigraphic sleep patterns (total sleep time [MD = 18.09 min; SMD = 0.32], sleep onset latency [MD = 11.96 min; SMD = 0.41]). Improvements in sleep (self-reported, not actigraphy) were maintained at follow-up, but few studies conducted follow-up assessments resulting in low-quality evidence. Reduction in total behavioral problems (SMD = 0.48) posttreatment and attention/hyperactivity (SMD = 0.28) at follow-up was found. Changes in cognition and academic skills were not examined in any studies.

CONCLUSIONS

BSIs improve sleep, at least in the short term, in children with NNDDs. Benefits may extend to functional improvements in behavior. More rigorous RCTs involving placebo controls, blinded outcome assessment, longer follow-up durations, and assessment of functional outcomes are required.

The persistence of sleep disturbance and its correlates in children with moderate to severe traumatic brain injury: A longitudinal study

OBJECTIVES

The primary aim was to examine whether sleep disturbances persist in children in the chronic stage of recovery from moderate or severe traumatic brain injury (TBI). The secondary aim was to examine whether memory difficulties and/or other previously identified factors relate to sleep disturbances in children with moderate to severe TBI.

METHODS

This longitudinal study included 21 children with moderate to severe TBI, 8-18 years old, recruited from an urban tertiary paediatric specialised brain injury rehabilitation unit. Participants were seen 5 years and again 7 years post-injury, on average. Sleep disturbances were assessed with Sleep Disturbance Scale for Children (SDSC). Correlates that were considered included indicators of TBI severity, and questionnaires assessing everyday memory, fatigue, internalizing and externalizing behaviors and pain intensity.

RESULTS

The SDSC scores of children with moderate to severe TBI indicated greater disturbances in initiating and maintaining sleep, arousal, sleep-wake transition, and excessive somnolence relative to the norms, at follow-up. The mean SDSC scores and the number of participants with subclinical to clinical sleep disturbances on the SDSC remained unchanged from baseline to follow-up. At follow-up, the SDSC initiating and maintaining sleep, and excessive somnolence scales were associated with poorer everyday memory and greater fatigue.

CONCLUSIONS

Children with moderate to severe TBI experience ongoing sleep disturbances for years post-injury. Greater sleep disturbances are associated with worse functional outcomes. Further research into sleep disturbances and development of treatments is important, as it could improve the outcomes of children with TBI.

Children who sustained traumatic brain injury take longer to fall asleep compared to children who sustained orthopedic injuries: actigraphy findings

Objective: Primary: to examine objective sleep outcomes in children who sustained moderate to severe traumatic brain injury (TBI). Secondary: to examine the relation of objective sleep with subjective sleep, fatigue, and injury variables.Setting: A single tertiary brain injury unit.Participants: Children (5-15 years) with moderate to severe TBI (n = 23) or orthopedic injury (OI; n = 13).Design: Cohort study.Measures: Primary: objective sleep measure (actigraphy watch). Secondary: subjective sleep measure (questionnaire), fatigue questionnaire, and injury variables.Results: On actigraphy, children with TBI had longer sleep onset latency compared to children with OI. On the sleep questionnaire, children with TBI obtained higher scores for total sleep disturbance, initiating and maintaining sleep, and excessive somnolence. On the fatigue questionnaire, greater difficulties were found for total, sleep/rest, and cognitive fatigue for the TBI group. In the TBI group, actigraphy data did not correlate with sleep questionnaire, fatigue, or injury variables.Conclusion: Our study showed evidence of objective and subjective sleep disturbance in children with moderate to severe TBI, but these two types of sleep measures were not related. It is possible that distinct mechanisms underpin objective and subjective sleep disturbance, which may require different interventions.

First stage international validation of the pediatric family needs questionnaire (FNQ-P)

OBJECTIVES

1. Evaluate reliability and construct validity of the newly-developed Family Needs Questionnaire - Pediatric (FNQ-P), a 40-item measure assessing the extent to which family's needs are met after a child has an acquired brain injury (ABI). 2. Explore the impact of selected child characteristics on FNQ-P scores.

RESEARCH DESIGN: MEASUREMENT STUDY

Methods: Parents/caregivers of children with ABI (2-18 years) were recruited across four sites (Canada, Sweden, Lithuania, Australia) for FNQ-P test-retest evaluation. These sites plus a fifth (United Kingdom) completed construct validity evaluation with the Family Burden of Injury Inventory and Strengths and Difficulties Questionnaire. Associations between FNQ-P score and age, injury severity, time post-injury and site were evaluated via stepwise regression.

RESULTS

FNQ-P mean scores (n=61) were 64.1% (SD 22.3) and 58.8% (SD 22.6) on test and retest, respectively. Test-retest reliability was good overall (ICC=0.78, 95% CI 0.65-0.86). There was a weak association between FNQ-P and FBII (r=-0.23, P=0.049, n=71), but no association between FNQ-P and SDQ scores (maximum r=0.16, P>0.15). None of the variables studied predicted FNQ-P scores.

CONCLUSION

The FNQ-P demonstrated good test-retest reliability. Further validity assessment is recommended. Lack of relationship between FNQ-P and variables studied suggests independence of family needs.

Opiate analgesics and testing of post traumatic amnesia in school-aged children

OBJECTIVE

To assess the validity of the Westmead PTA scale in school-aged children treated with opiate analgesics.

METHOD

Twenty-eight hospitalized children without brain injury, aged between 8 and 16 years treated with opiate analgesics for pain relief following surgery were tested on the Westmead PTA scale. Pain and stress levels were also self-reported each day.

RESULTS

Only 29% (n = 7) of children assessed over four days obtained a maximum score of 12/12 on three consecutive days, thus 71% would have been deemed to have been in PTA when they were not. The percentage of children who obtained a maximum score significantly decreased over consecutive days of assessment, due to an increase in error rate on picture memory items. Self-reported pain and stress ratings were not correlated with PTA scores.

CONCLUSIONS

Opiate analgesia can disrupt performance on the Westmead PTA scale in school-aged children resulting in a high false-positive error rate. It is therefore important to record pain medication schedules and interpret results cautiously when opiate analgesia is used following a TBI. Alteration of the method of administration of the memory items should be researched as this may increase the validity of the scale for children with TBI treated with opiate analgesics.

A feasibility and acceptability study of cognitive behavioural treatment for insomnia in adolescents with traumatic brain injury: A-B with follow up design, randomized baseline, and replication across participants

Difficulties falling asleep or staying asleep (symptoms of insomnia) are common following paediatric traumatic brain injury (TBI). Yet, interventions to treat insomnia in this population have not yet been reported. This single-case series examined the feasibility and acceptability of cognitive behavioral treatment for insomnia (CBT-I) for adolescents (n = 5, aged 11-13 years) with TBI, and explored changes in sleep and fatigue post-treatment. Adolescents were randomly assigned to two conditions: a 7- or 14-days baseline, followed by 4 weeks of manualised CBT-I delivered individually. To assess feasibility and acceptability we compared recruitment and retention rates, and questionnaire scores to a-priori set criteria. We explored treatment efficacy and functional gains in sleep and fatigue from baseline to follow-up using structured visual analysis of time-series graphs, and reliable change indices or changes in clinical classification. Feasibility and acceptability indicators met a-priori criteria, but therapists noticed limited adolescent engagement in sessions. Clinically significant improvements were found in sleep, in 3 out of 4 cases, and fatigue, in all cases. Our study provides preliminary evidence that CBT-I is feasible for insomnia treatment in adolescents with TBI and provides directions for development of future treatment studies.

Preliminary validation study of the Sydney Post-Traumatic Amnesia Scale (SYPTAS) in children with traumatic brain injury aged 4 to 7 years

The aim of this study was to assess the validity (developmental, concurrent, and predictive) of the Sydney Post-Traumatic Amnesia Scale (SYPTAS) for assessment of post-traumatic amnesia (PTA) in 4 to 7 year old children with traumatic brain injury (TBI). The design of this study is a retrospective cohort study. The SYPTAS was administered to 35 children (26 boys) aged 4.0 to 7.8 years who were consecutively admitted to a children's hospital with mild (n = 26), moderate (n = 3), or severe (n = 7) TBI. Concurrent validity of the SYPTAS was assessed against the Glasgow Coma Scale Scores (GCS). Predictive validity of the SYPTAS for functional outcomes was evaluated against the King's Outcome Scale for Childhood Head Injury (KOSCHI) at discharge and outpatient follow-ups. The length of PTA, measured by the SYPTAS, was invariant of children's chronological age, confirming the scale's developmental validity. Longer PTA was associated with lower GCS, endorsing concurrent validity of PTA duration measured by the SYPTAS, as a clinical indicator of TBI severity. PTA duration measured by the SYPTAS was a significant predictor of functional outcomes on the KOSCHI at discharge and follow-ups. This study provides evidence that the SYPTAS has good developmental, concurrent and predictive validity for assessment of PTA in children aged 4 to 7 years. PTA duration assessed by the SYPTAS is a clinical indicator of TBI severity and can aid rehabilitation planning post TBI.

The Successful Delivery of Megaprojects: A Novel Research Method

Megaprojects are often associated with poor delivery performance and poor benefits realization. This article provides a method of identifying, in a quantitative and rigorous manner, the characteristics related to project management success in megaprojects. It provides an investigation of how stakeholders can use this knowledge to ensure more effective design and delivery for megaprojects. The research is grounded in 44 mega-projects and a systematic, empirically based methodology that employs the Fisher's exact test and machine learning techniques to identify the correlation between megaprojects’ characteristics and performance, paving the way to an understanding of their causation.

PTA scale for children aged 4 to 7 years: Selecting developmentally valid and reliable items

The aim of this study was to select developmentally valid and reliable items for inclusion in criterion-referenced (pass > 90%) posttraumatic amnesia (PTA) scale for children aged 4 to 7 years in a prospective cohort study. Fifty-two typically developing children (26 male/26 female) aged 4 to 7 years were administered a set of 10 items (5 orientation, 5 memory) over 3-4 days. The total score obtained on the set of 10 items had poor developmental validity and test-retest reliability. Nevertheless, individual item analysis identified five items (three orientation and two memory items) that were consistently passed by >90% of the children on each day of testing. For these five items the total scores did not differ significantly either between age groups or between days of testing. Test-retest was extremely high (close to 1). The five items had excellent developmental validity and test-retest reliability. This study identified 5 (3 orientation and 2 memory) items that met our selection criterion and form a new PTA scale, the Sydney PTA scale (SYPTAS), for children aged 4 to 7 years.

Special Purpose Entities in Megaprojects: Empty Boxes or Real Companies?

Megaprojects involve organizations called “Special Purpose Entities” (SPEs) also known as “special purpose vehicles.” Despite their relevance, particularly for governance, SPEs are under-investigated. In the project management literature, there is neither a widely accepted definition of SPEs nor a clear understanding of what it does. This article presents an extensive literature review, which considers three domains: legal, financial, and project management. Four outcomes are presented: the definition of SPE, the typology of existing SPEs, comparisons of existing SPEs, and descriptions of SPE uses in megaprojects.

Assessing psychosocial functioning following childhood acquired brain injury: The Sydney Psychosocial Reintegration Scale for Children

OBJECTIVE

The Sydney Psychosocial Reintegration Scale for Children (SPRS-C) assesses psychosocial functioning in children with acquired brain injury (ABI). This article aims to: (1) describe normative data for the parent-rated SPRS-C and, (2) evaluate the discriminant validity of the SPRS-C.

METHODS

For Aim 1, participants were parents of typically developing children (TDC) aged 5-14 years (N = 200). For Aim 2, participants with ABI were aged 5-14 years (n = 26). A matched group of TDC was sampled from the larger normative sample to serve as a control group (n = 26).

RESULTS

For Aim 1, SPRS-C scores across the 10 age-bands were in the higher ranges. Correlation coefficients of SPRS-C total score with child's age and parent occupational skill level were not statistically significant. For Aim 2, SPRS-C scores for the ABI group were significantly lower than the control group.

CONCLUSIONS

These data provide a guide for clinical interpretation of the SPRS-C for measuring psychosocial functioning in children with ABI.

Duration of post-traumatic amnesia as a predictor of functional outcome in school-age children: a systematic review

AIM

In adults, duration of post-traumatic amnesia (PTA) is a powerful early predictor of functional outcomes in traumatic brain injury. The aim of this work was to assess the predictive validity of PTA duration for outcomes in children (6-18y).

METHOD

PsycINFO, MEDLINE, Web of Science, and Embase were searched for papers published to January 2014. Ten studies met inclusion criteria: they used standardized instruments to assess PTA and functional outcomes, and examined relationships between the two. Outcomes were classified according to (1) the International Classification of Functioning, Disability and Health (ICF) core sets for neurological conditions for post-acute care and (2) global functioning and quality of life. Methodological quality was rated for each study.

RESULTS

The search identified 10 studies of moderate mean quality (M=11.8 out of 18). Longer PTA duration related to worse functional outcomes: global functioning and in the two ICF categories ('body function', 'activities and participation'). Relationships between PTA duration and quality of life and the ICF category of 'body structure' were not examined. PTA duration was, in 46 out of 60 (76.67%) instances, a stronger predictor of outcomes than other indices of injury severity.

CONCLUSION

Longer PTA duration is a valid predictor of worse outcomes in school-age children. Thus, PTA should be routinely assessed in children after traumatic brain injury.

Natural sequence of recovery from child post-traumatic amnesia: A retrospective cohort study

The aim of this study was to determine the sequence of skills recovery during post-traumatic amnesia (PTA) in children with moderate to severe traumatic brain injuries (TBIs).

SETTING

Fifty children aged 8 to 15 years consecutively admitted to a children's hospital with TBI and PTA>24 were tested in a retrospective cohort study where the main measure was the Westmead PTA Scale (WPTAS). The group analyses show that orientation to time took longer to recover than orientation to person and place, but not memory, while the individual analyses revealed that when orientation to time was grouped with memory, 94% of children recovered orientation to person and place before orientation to time and memory (examiner and pictures). Correlation coefficients between age and the number of days taken to recover skills were not found to be significant. It was established that, in terms of the natural sequence of skills recovery in children aged 8 to 15 years following moderate to severe TBI, recovery of orientation to time is more closely aligned to memory than to orientation to person and place. It was also established that WPTAS items are developmentally appropriate for children aged 8 to 15 years who have sustained TBI. These findings are clinically important because monitoring recovery from PTA both impacts the rehabilitation offered to individuals during acute care and aids discharge planning.

Guiding practice development using the Tidal Commitments

The Tidal Model of Mental Health Recovery has contributed to the transformation of nursing practice at the Royal Ottawa Hospital (ROH), a psychiatric and mental health facility in Ontario, Canada. Ten commitments affirm the core values of the Tidal Model. These commitments guide person-centred, collaborative, strength-based practice and they facilitate Tidal teaching. In this paper we illustrate fidelity to the values, principles and processes of the model and the commitments while implementing the model. We share how some of the commitments are realized in our Tidal teaching and provide examples of successes and challenges.

Transfer of glutamine between astrocytes and neurons

The export of glutamine from astrocytes, and the uptake of glutamine by neurons, are integral steps in the glutamate-glutamine cycle, a major pathway for the replenishment of neuronal glutamate. We review here the functional and molecular identification of the transporters that mediate this transfer. The emerging picture of glutamine transfer in adult brain is of a dominant pathway mediated by system N transport (SN1) in astrocytes and system A transport (SAT/ATA) in neurons. The participating glutamine transporters are functionally and structurally related, sharing the following properties: (a) unlike many neutral amino acid transporters which have proven to be obligate exchangers, these glutamine transporters mediate net substrate transfer energized by coupling to ionic gradients; (b) they are sensitive to small pH changes in the physiological range; (c) they are susceptible to adaptive and humoral regulation; (d) they are related structurally to the AAAP (amino acid and auxin permeases) family of transporters. A key difference between SN1 and the SAT/ATA transporters is the ready reversibility of glutamine fluxes via SN1 under physiological conditions, which allows SN1 both to sustain a glutamine concentration gradient in astrocytes and to mediate the net outward flux of glutamine. It is likely that the ASCT2 transporter, an obligate exchanger of neutral amino acids, displaces the SN1 transporter as the main carrier of glutamine export in proliferating astrocytes.

Functional integration of the transport of ammonium, glutamate and glutamine in astrocytes

This short review surveys the effects of extracellular potassium, released by neuronal activity, on the fluxes of ammonium, glutamate and glutamine in astrocytes. There is evidence that each of these fluxes is modulated by potassium-induced changes in astrocytic pH. The result is viewed as an integrated response to neuronal activity. The unusually high permeability of astrocyte cell membrane to ammonium ions, together with the normal transmembrane gradient of pH, enables astrocytes to accumulate ammonium appreciably. However, at loci of neuronal activity, effective ammonium ion permeability is diminished and the cytosol is alkalinized, resulting in a local decline in intracellular ammonium concentration. Intracellular potassium concentration rises at these same loci, creating the conditions for a 'potassium-ammonium countercurrent' in which ammonium ions migrate intracellularly towards sites of neuronal activity as potassium ions diffuse away. Physiologic elevations of extracellular potassium evoke a marked 'paradoxical' increase in the velocity of glutamate uptake in astrocytes. This increase correlates well with the extent of potassium-induced alkalinization. Further, recent evidence identifies a major transporter of glutamine in astrocytes (System N) as a glutamine/proton exchanger. Potassium can reverse the transmembrane gradient of protons in astrocytes, and increase intracellular glutamine concentration, creating the conditions for a reversal of glutamine flux via System N from uptake to export. These flux changes, evoked by potassium released from active neurons, combine to accelerate glutamate-glutamine cycling.

The astroglial ASCT2 amino acid transporter as a mediator of glutamine efflux

Glutamine release from astrocytes is an essential part of the glutamate-glutamine cycle in the brain. Uptake of glutamine into cultured rat astrocytes occurs by at least four different routes. In agreement with earlier studies, a significant contribution of amino acid transport systems ASC, A, L, and N was detected. It has not been determined whether these systems are also involved in glutamine efflux or whether specific efflux transporters exist. We show here that ASCT2, a variant of transport system ASC, is strongly expressed in rat astroglia-rich primary cultures but not in neuron-rich primary cultures. The amino acid sequence of rat astroglial ASCT2 is 83% identical to that of mouse ASCT2. In Xenopus laevis oocytes expressing rat ASCT2, we observed high-affinity uptake of [U-14C]glutamine (Km = 70 microM) that was Na(+)-dependent, concentrative, and unaffected by membrane depolarization. When oocytes were preloaded with [U-14C]glutamine, no glutamine efflux was detected in the absence of extracellular amino acids. Neither lowering intracellular pH nor raising the temperature elicited efflux. However, addition of 0.1 mM unlabeled alanine, serine, cysteine, threonine, glutamine, or leucine to the extracellular solution resulted in a rapid release of glutamine from the ASCT2-expressing oocytes. Amino acids that are not recognized as substrates by ASCT2 were ineffective in this role. Extracellular glutamate stimulated glutamine release weakly at pH 7.5 but was more effective on lowering pH to 5.5, consistent with the pH dependence of ASCT2 affinity for glutamate. Our findings suggest a significant role of ASCT2 in glutamine efflux from astrocytes by obligatory exchange with extracellular amino acids. However, the relative contribution of this pathway to glutamine release from cells in vivo or in vitro remains to be determined.

Intracellular acidification induced by passive and active transport of ammonium ions in astrocytes

We describe an unconventional response of intracellular pH to NH4Cl in mouse cerebral astrocytes. Rapid alkalinization reversed abruptly to be replaced by an intense sustained acidification in the continued presence of NH4Cl. We hypothesize that high-velocity NH4+ influx persisted after the distribution of ammonia attained steady state. From the initial rate of acidification elicited by 1 mM NH4Cl in bicarbonate-buffered solution, we estimate that NH4+ entered at a velocity of at least 31.5 nmol.min-1.mg protein-1. This rate increased with NH4Cl concentration, not saturating at up to 20 mM NH4Cl. Acidification was attenuated by raising or lowering extracellular K+ concentration. Ba2+ (50 microM) inhibited the acidification rate by 80.6%, suggesting inwardly rectifying K+ channels as the primary NH4+ entry pathway. Acidification was 10-fold slower in rat hippocampal astrocytes, consistent with the difference reported for K+ flux in vitro. The combination of Ba2+ and bumetanide prevented net acidification by 1 mM NH4Cl, identifying the Na(+)-K(+)-2Cl- cotransporter as a second NH4+ entry route. NH4+ entry via K+ transport pathways could impact "buffering" of ammonia by astrocytes and could initiate the elevation of extracellular K+ concentration and astrocyte swelling observed in acute hyperammonemia.

Intracellular pH as a regulatory signal in astrocyte metabolism

An intracellular alkalinization is observed in mammalian astrocytes in response to repetitive neuronal activity in vivo. The alkalinizing effect of potassium released from electrically active neurons predominates over many other influences on the intracellular pH of astrocytes, including acid loads induced by glutamate and ammonium. There is evidence that this pH signal, elicited by neuronal activity, may facilitate glucose utilization and glutamine formation in astrocytes. This short review surveys the mechanisms of the intracellular pH changes induced in astrocytes by extracellular potassium, glutamate, and ammonium. It then focuses upon the regulatory effects of these pH changes on glucose utilization, as estimated primarily by rates of deoxyglucose phosphorylation, and on the uptake and metabolism of glutamate. Many studies in this field exploit the advantages of astrocyte cell culture. However, the conditions of cell culture can diminish expression of the intracellular alkalinization induced by potassium and thus lead to underestimation of the metabolic significance of this pH signal.

Characterization of L-alpha-aminoadipic acid transport in cultured rat astrocytes

The mechanism of the selective gliotoxicity of L-alpha-aminoadipate (L-alpha AA) is thought to involve its entry into glia as a substrate for glutamate transporters or, alternatively, its ability to inhibit glial glutamate transport. To clarify the properties of L-alpha AA as a transport substrate, we explored the ionic dependence, kinetics and pharmacology of L-[3H] alpha AA uptake in rat cortical astrocytes. We observed two components of saturable L-alpha AA uptake, one Na(+)-dependent and the other Na(+)-independent. These components exhibited the characteristics of system X-AG, the widespread family of Na(+)-cotransporters of aspartate and glutamate, and system x-c, a Cl(-)-dependent glutamate/cystine exchanger, respectively. The K(m) value of Na(+)-dependent L-alpha AA uptake was 629 +/- 42 microM, and Vmax was 62 +/- 4 nmol.min-1.mg-1 protein, which was more than twice the capacity of Na(+)-dependent glutamate uptake. The kinetic parameters of Na(+)-dependent L-alpha AA uptake (K(m) of 20 +/- 2 microM, Vmax of 1.7 +/- 0.4 nmol.min-1.mg-1 protein did not differ from the values for Na(+)-independent glutamate uptake, indicating that L-alpha AA and glutamate are equally good substrates for system x-c.

Mercuric chloride uncouples glutamate uptake from the countertransport of hydroxyl equivalents

The cotransport of sodium and glutamate by system X(AG)- is believed to be coupled to the countertransport of potassium and hydroxyl ion equivalents. Accordingly, the uptake of glutamate or D-aspartate in astrocytes is accompanied by an intracellular acidification. Here, we report that HgCl2 blocks the glutamate-induced acidification with an approximate 50% inhibitor concentration (IC50) of 55 nM, an order of magnitude below its IC50 for inhibition of glutamate uptake. At 100 nM HgCl2, glutamate-induced acidification was abolished, whereas glutamate uptake was unaffected. D-Aspartate-induced acidification was equally sensitive to HgCl2, indicating that HgCl2 blocked a transporter-mediated, rather than a receptor-mediated, acidification. Unaltered responses to acute acid and alkaline loads showed that HgCl2 was not acting indirectly via a change in pH regulation. We conclude that HgCl2 acted directly on the glutamate transporter to uncouple the uptake of glutamate from the export of hydroxyl equivalents. In contrast, two other sulfhydryl reagents, p-chloromercuribenzensulfonate and N-ethylmaleimide, failed to discriminate between glutamate-induced acidification and glutamate uptake. An additional effect of > or = 100 nM HgCl2, in this case shared by p-chlormercuribenzenesulfonate, was transient intracellular acidification. There is evidence that glutamate transport is regulated by intracellular pH. Mercuric mercury may disrupt the regulation of glutamate transport at lower concentrations than those that block transport.

Glutamine transport in mouse cerebral astrocytes

We measured initial influx and exchange of [14C]glutamine in primary astrocyte cultures in the presence and absence of Na+. Kinetic analysis of transport in Na+ -free solution indicated two saturable Na+ -independent components, one of which was identifiable functionally as system L1 transport. In the presence of Na+, multiple hyperbolic components were not resolvable from the kinetic data. Nevertheless, other evidence supported participation by at least three Na+ -dependent neutral amino acid transporters (systems A, ASC, and N). System A transport of glutamine was usually absent or minimal, based on lack of inhibition by alpha-(methylamino) isobutyric acid. However, vigorous system A-mediated transport emerged after derepression by substrate deprivation. Participation by system ASC was indicated by trans-acceleration of Na+ -dependent uptake, preferential inhibition of an Li+ -intolerant component of uptake by cysteine, and inhibition by cysteine of a component resistant to inhibition by histidine and alpha-(methylamino) isobutyric acid. Because nonsaturable transport of glutamine appeared negligible, and system L transport of glutamine was suppressed in the presence of Na+, low-affinity system ASC transport may be the major route of export of glutamine from astrocytes. At 700 microM glutamine, the primary uptake route was system N transport, identified on the basis of selective inhibition by histidine and asparagine, pH sensitivity, and tolerance of Li+ in place of Na+.

Potassium-induced stimulation of glutamate uptake in mouse cerebral astrocytes: the role of intracellular pH

The Na(+)-glutamate cotransporters are believed to countertransport OH- and K+. Previous evidence that the velocity of glutamate uptake can exceed the acid extrusion capacity of astrocytes raised the question of whether intracellular pH can become rate limiting for glutamate uptake. Cytoplasmic buffering capacity and acid extrusion in astrocytes are partially HCO3- dependent. Also, it was reported recently that raising extracellular [K+] alkalinizes astrocyte cytoplasm by an HCO3- dependent mechanism. Here, we have compared glutamate uptake in HCO3(-)-buffered and HCO3(-)-depleted solutions at varying [K+]. We observed a pronounced stimulation of glutamate uptake by extracellular K+ (3-24 mM) that was substantially HCO3- dependent and affected preferentially the uptake of high concentrations (> 25 microM) of glutamate. Stimulation of uptake by low extracellular [K+] (1.5-3 mM) was less dependent on HCO3-. Potassium-induced stimulation of uptake was weaker in rat astrocyte cultures than in mouse. The effects of Ba2+ and amiloride on glutamate uptake, as well as the HCO3(-)-dependent stimulatory effects of K+ and the species difference, all related consistently to effects on intracellular pH. The effects on uptake, however, were much larger than predicted by the associated changes in electrochemical gradient of OH-. A "bimodal" scheme for glutamate transport can account qualitatively for the observed correlation between intracellular pH and velocity of glutamate uptake.

K(+)-induced alkalinization in mouse cerebral astrocytes mediated by reversal of electrogenic Na(+)-HCO3- cotransport

Raising extracellular K+ concentration ([K+]o) induces an alkaline shift of intracellular pH (pHi) in astrocytes. The mechanism of this effect was examined using the fluorescent pHi indicator 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein in primary cultures of mouse cerebral astrocytes. Raising [K+]o from 3 to 12 mM increased pHi by 0.28 pH units in 26 mM HCO(3-)-buffered solution. In nominally HCO(3-)-free solution (containing approximately 95 microM HCO3-), the alkalinization fell to 0.21 pH units and further to 0.08 pH units on removal of atmospheric CO2, suggesting a process with high affinity for HCO3-. This effect was Na+ dependent, Cl- independent, and inhibited by 0.5 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, indicating the involvement of Na(+)-HCO3- cotransport. The relationship between pHi and log[K+]o was found to be linear and to predict a stoichiometry of at least two HCO3- transported with each Na+. After removal of exogenous CO2/HCO3-, the direction of changes in pHi elicited by adding 1 mM HCO3- showed that net flux of HCO3- via the Na(+)-HCO3- cotransporter was outward at rest and was reversed by depolarization.

Extracellular potassium regulates the glutamine content of astrocytes: mediation by intracellular pH

Based upon previous evidence that glutamine formation in astrocytes is pH-sensitive and that raised extracellular K+ alkalinizes astrocytic cytoplasm, it was hypothesized that extracellular K+ might regulate glutamine formation. In this study, the free glutamine content of mouse cerebral astrocytes incubated with 0.1 mM glutamate and 0.1 mM ammonium increased by 80-90% when the extracellular K+ concentration was raised from 3 to 12 mM. The corresponding K(+)-induced intracellular alkalinization of +0.13 pH units only partially reversed a glutamate-induced intracellular acidification of -0.24 pH units. By comparison, adjustment of extracellular pH from 7.4 to 7.8 shifted intracellular pH by +0.25 pH units, fully reversing the glutamate-induced acidification and increasing glutamine content by 120-180%. The effect of K+ on intracellular pH increased to +0.25 pH units in bicarbonate-buffered solution, suggesting that the regulation of glutamine formation by extracellular K+ is enhanced in the presence of bicarbonate.

Interaction between the glutamine cycle and the uptake of large neutral amino acids in astrocytes

When astrocyte cultures are incubated with glutamate and ammonium, the clearance of these substrates followed by the formation and export of glutamine simulates the action of the "glutamine cycle" that is believed to function in the CNS. In the present study this process was found to increase the uptake of large neutral amino acids (LNAAs), namely, histidine, kynurenine, leucine, phenylalanine, and tryptophan, by two- to threefold in mouse cerebral astrocytes. The enhancement of kynurenine uptake was shown to depend on the formation of glutamine and to saturate at low levels of glutamine. LNAAs transiently lowered the glutamine content of astrocytes that were incubated with glutamate and ammonium, but they did not affect net export of glutamine to the solution at normal physiological pH. However, on adjustment of the pH of the solution to 7.8, which causes a large increase in glutamine content without affecting export, kynurenine now significantly increased net glutamine export. These findings relate to proposed mechanisms of cerebral dysfunction in hyperammonemia.

Regulation of the glutamine content of astrocytes by cAMP and hydrocortisone: Effect of pH

It was reported recently that the glutamine content of astrocytes incubated with glutamate and ammonium is steeply dependent on the pH of the solution. The present study shows that pretreatment of astrocytes with dibutyryl cAMP or with hydrocortisone, conditions that induce glutamine synthetase activity, increased glutamine content 2.4-fold and 5.3-fold, respectively. Nevertheless, a shift of pH from 7.4 to 7.8 increased glutamine content further by 2.7-fold and 3.0-fold, respectively. The net rates of uptake of glutamate and export of glutamine varied narrowly compared to these very large changes in glutamine content.

In vitro evidence for the hole of glutamate in the CNS toxicity of mercury

Intoxication with elemental mercury vapor or with methylmercury results in the accumulation of mercuric mercury (Hg2+) in the brain. Submicromolar concentrations of Hg2+ were shown previously to inhibit glutamate uptake in astrocyte cultures selectively and reversibly. This finding suggests that blockade of the inactivation of synaptically released glutamate is a potential mechanism of the CNS toxicity of Hg2+. The present study shows further that Hg2+ (< or = 1 microM): (i) markedly inhibits the clearance of extracellular glutamate both by astrocyte cultures and by spinal cord cultures; (ii) reduces glutamine content and export in astrocyte cultures; (iii) has little effect on neuronal viability in spinal cord cultures in the absence of excitotoxic accumulations of glutamate; (iv) does not impair the sensitivity of neurons to the excitotoxic action of glutamate. Also, it is noted that Hg2+ (< or = 1 microM) has not been shown to impair transmitter release acutely in existing studies of presynaptic actions. Thus, the available evidence from in vitro studies is consistent with the hypothesis that low concentrations of mercuric mercury in the brain can cause neurotoxicity by selectively inhibiting the uptake of synaptically released glutamate, with consequent elevation of glutamate levels in the extracellular space.

Effect of pH on Glutamine Content Derived from Exogenous Glutamate in Astrocytes

A shift in pH from 7.4 to 7.8 in the incubation solution caused a 3.4-fold increase in the free glutamine content of mouse cerebral astrocytes that were incubated with glutamate (100 microM) and ammonium (100 microM). This large and reversible steady-state increase in glutamine content was accompanied by smaller transient increases in the following: (a) net formation of glutamine; (b) clearance of glutamate from the incubation solution; and (c) glutamate content. The content of glutamine was reduced markedly by omission of either glutamate or ammonium from the incubation solution, or by inhibition of glutamine synthetase activity with methionine sulfoximine. The rate at which glutamine was exported from the astrocytes was unaffected by the pH change. The effects of pH on the concentration of free ammonia or on glutamate uptake do not appear to mediate the increase in glutamine content. Uptake of exogenous glutamine was little affected by the pH change. Therefore, possible mediation of the effect by an increase in intracellular pH must be considered. The response to altered pH described here may provide a cellular basis for the increased level of brain glutamine observed in hyperammonemia.

Effect of intracellular glutamine on the uptake of large neutral amino acids in astrocytes: concentrative Na(+)-independent transport exhibits metastability

To examine whether the concentration gradient of glutamine (Gln) drives concentrative Na(+)-independent uptake of neutral amino acids (NAA) in mouse cerebral astrocytes, uptake was compared in "Gln-depleted" and "Gln-replete" cultures. Uptake (30 min in Na(+)-free buffer) of histidine, kynurenine, leucine, tyrosine, and a model substrate for System L transport was 70-150% greater in Gln-replete cultures. Phenylalanine uptake was not affected. All of these NAA trans-stimulated the export of Gln from astrocytes. However, the increase in NAA uptake was sustained even though the Gln content of Gln-replete cultures declined. Also, uptake of Gln itself was enhanced in Gln-replete cultures. Thus, countertransport of Gln was insufficient to explain the enhancement of NAA uptake. Enhanced uptake was restored, and could be magnified, by reloading Gln-depleted cultures either with Gln or with histidine. It is suggested that substrate-induced asymmetry and molecular hysteresis in the Na(+)-independent carrier could account for the sustained enhancement of NAA uptake. Only histidine and kynurenine were concentrated comparably to Gln (15- to 29-fold at 1 mM in Na(+)-free buffer). The other NAA were four to six times less concentrated. At least two Na(+)-dependent transport systems also supported the concentration gradient of Gln in regular buffer.

Inhibition of amino acid transport and protein synthesis by HgCl2 and methylmercury in astrocytes: selectivity and reversibility

The previously reported observation that submicromolar concentrations of HgCl2 inhibit glutamate uptake reversibly in astrocytes, without effect on 2-deoxyglucose uptake, suggested that elemental mercury vapor, which is oxidized to mercuric mercury in the brain, might cause neurodegenerative change through the mediation of glutamate excitotoxicity. Here, selectivity is explored further by measuring the inhibition of other amino acid transporters and protein synthesis as a function of HgCl2 concentration. The properties of MeHgCl were compared under identical conditions, and some morphological correlates of function were examined. Inhibition of amino acid transport by HgCl2 was selective, whereas MeHgCl was nonselective. The 50% inhibitory concentrations of HgCl2 for uptake of alpha-aminoisobutyric acid by system A, uptake of alpha-aminoisobutyric acid or kynurenine by a system L variant, and uptake of gamma-aminobutyric acid were all two- to fourfold greater than that for uptake of glutamate. The submicromolar concentrations of HgCl2 that inhibited glutamate transport also inhibited protein synthesis, but in a rapidly reversible fashion, and elicited only discrete ultrastructural changes (heterochromatin, increased numbers of lysosomal bodies, and increased complexity of cell surface). In contrast, inhibition of protein synthesis by MeHgCl was acutely (1-h) irreversible and became marked only at concentrations higher than those that elicited gross morphologic change in the form of "bleb"-like swellings. The results lend support to the proposed excitotoxic mediation of mercury vapor neurotoxicity and reveal a sharp contrast between the effects of HgCl2 and MeHgCl on astrocytes.

High-affinity uptake of L-kynurenine by a Na+-independent transporter of neutral amino acids in astrocytes

L-Kynurenine (KYN), an intermediary product in the kynurenine pathway of tryptophan metabolism, is the common precursor from which are formed both quinolinic acid, a potent endogenous "excitotoxin," and kynurenic acid, a nonselective antagonist of excitotoxins. The present work examines 3H-KYN transport in primary astrocyte cultures derived from the cerebra of newborn mice. Influx and efflux of 3H-KYN were attributable almost entirely to carrier-mediated transport. The tritium recovered in uptake experiments was identifiable as 3H-KYN, indicating a low rate of KYN metabolism during incubations up to 30 min. KYN uptake decreased in the presence of extracellular Na+, at least in part because KYN efflux was accelerated. Marked trans stimulation of KYN efflux by extracellular KYN provided evidence of the exchanging nature of the carrier. Saturation curves for the initial velocity of KYN uptake conformed to a 1-component saturable system with Km of 32 microM and Vmax of 2.1 nmol mg-1 protein min-1. KYN was notably concentrated by the astrocytes, with an estimated steady-state distribution ratio of 180-fold for 1 microM KYN. Analog inhibition studies showed that the KYN transporter exhibited a clear preference for large neutral amino acids; leucine, tryptophan, and phenylalanine were recognized with relatively higher affinity than KYN. In summary, KYN is concentratively transported into astrocytes by a Na+-independent exchanger with high affinity for branched-chain and aromatic neutral amino acids. The substrate specificity and high affinity of this transport system resemble the properties of neutral amino acid transport across the blood-brain barrier in the rat and human.

Neutral amino acid transport in astrocytes: characterization of Na+-dependent and Na+-independent components of alpha-aminoisobutyric acid uptake

Neutral amino acid transport is largely unexplored in astrocytes, although a role for these cells in blood-brain barrier function is suggested by their close apposition to cerebrovascular endothelium. This study examined the uptake into mouse astrocyte cultures of alpha-aminoisobutyric acid (AIB), a synthetic model substrate for Na+-dependent system A transport. Na+-dependent uptake of AIB was characteristic of system A in its pH sensitivity, kinetic properties, regulatory control, and pattern of analog inhibition. The rate of system A transport declined markedly with increasing age of the astrocyte cultures. There was an unexpectedly active Na+-independent component of AIB uptake that declined less markedly than system A transport as culture age increased. Although the saturability of the Na+-independent component and its pattern of analog inhibition were consistent with system L transport, the following properties deviated: (1) virtually complete inhibition of Na+-independent AIB uptake by characteristic L system substrates, suggesting unusually high affinity of the transporter; (2) apparent absence of trans-stimulation of AIB influx; (3) unusually concentrative uptake at steady state (the estimated distribution ratio for 0.2 mM AIB was 55); and (4) susceptibility to inhibition by N-ethylmaleimide. Direct study of the uptake of system L substrates in astrocytes is needed to confirm the present indications of high affinity and concentrative Na+-independent transport.

Specificity and reversibility of the inhibition by HgCl2 of glutamate transport in astrocyte cultures

Inhibition of glutamate transport is a potential indirect cause of excitotoxic damage by glutamate in the CNS. The mercuric ion, the form in which metallic mercury vapor is believed to exert its neurotoxic action, is a known inhibitor of amino acid transport. This study examines the specificity with which HgCl2 inhibits glutamate transport in mouse cerebral astrocytes by means of comparative measurements of 2-deoxyglucose uptake. Uptake of 2-deoxyglucose is an index of glucose utilization that reflects the function of Na+,K+-ATPase and hexokinase, and is sensitive to Na+ entry. The kinetic parameters, ionic dependence, and substrate specificity of glutamate transport in these astrocyte cultures were consistent with the commonly occurring system designated X-AG. Acute exposure to 0.5 microM HgCl2 inhibited by 50% the initial rate of glutamate transport but did not affect 2-deoxyglucose uptake. Glutamate transport was not detectably inhibited by Al2+, Pb2+, Co2+, Sr2+, Cd2+, or Zn2+ (10 microM as chlorides). The inhibitory action of 0.5 microM HgCl2 on glutamate transport was rapidly reversible. The action of 1-2 microM HgCl2 was progressive when exposures were extended to 1-3 h, and was more slowly reversible. These results suggest that Hg2+ can impair glial glutamate transport reversibly at exposure levels that do not compromise some other vital cell functions.

Effect of monensin on deoxyglucose uptake in cultured astrocytes: energy metabolism is coupled to sodium entry

This study was undertaken to measure the effect of maximal stimulation of sodium pump activity on the rate of energy metabolism in mouse cerebral astrocytes. The rate of uptake of 3H-2-deoxyglucose (3H-2-DG) was measured in astrocyte cultures sodium-loaded either by incubation in a K+-deficient solution or by use of the carboxylic sodium ionophore monensin. Sodium-loading by the first method caused 3H-2-DG uptake to increase by 80%, but the effect was brief (about 5 min) compared with the period of uptake measurement (20 min). In contrast, the presence of monensin (20 microM) caused a sustained 3.4-fold increase in the rate of 3H-2-DG uptake. The concentration-response relationship for monensin indicated a Kd of 1.5 microM and a maximum uptake enhancement of approximately fourfold. The monensin-stimulated uptake of 3H-2-DG was totally inhibited by incubation of the cultures in either K+-free or Na+-free solutions, or in the presence of ouabain (0.4 mM), indicating that the enhancement of uptake was the result of Na+ influx and sodium pump activation. These results raise the possibility that astroglia contribute significantly to regional variations in glucose consumption associated with functional activity in the brain. Ultrastructural analysis showed that sodium-loading in K+-free solution caused swelling confined to the trans face of Golgi stacks. However, monensin (5 microM) caused swelling of the entire Golgi stack, with progressively more severe swelling from cis to trans cisternae and formation of cytoplasmic vacuoles.(ABSTRACT TRUNCATED AT 250 WORDS)

Determinants of deoxyglucose uptake in cultured astrocytes: the role of the sodium pump

Glucose utilization in primary cell cultures of mouse cerebral astrocytes was studied by measuring uptake of tracer concentrations of [3H]2-deoxyglucose ([3H]2-DG). The resting rate of glucose utilization, estimated at an extracellular K+ concentration ([K+]o) of 5.4 mM, was high (7.5 nmol glucose/mg protein/min) and was similar in morphologically undifferentiated and "differentiated" (dibutyryl cyclic AMP-pretreated) cultures. Resting uptake of [3H]2-DG was depressed by ouabain, by reducing [K+]o, and by cooling. These observations suggest that resting glucose utilization in astrocytes was dependent on sodium pump activity. Sodium pump-dependent uptake in 2-3-week-old cultures was about 50% of total [3H]2-DG uptake but this fraction declined with culture age from 1 to 5 weeks. Uptake was not affected by changes in extracellular bicarbonate concentration ([HCO3-]o) in the range of 5-50 mM but was significantly reduced in bicarbonate-free solution. At high [HCO3-]o (50 mM) uptake was insensitive to pH (pH 6-8), whereas at low [HCO3-]o (less than 5 mM) uptake was markedly pH-dependent. Elevation of [K+]o from 2.3 mM to 14.2-20 mM (corresponding to extremes of the physiological range of [K+]o) resulted in a 35-43% increase in [3H]2-DG uptake that was not affected by culture age or by morphological differentiation. Our results indicate a high apparent rate of glucose utilization in astrocytes. This rate is dynamically responsive to changes in extracellular K+ concentration in the physiological range and is partially dependent on sodium pump activity.

Interactions of bupivacaine with ionic channels of the nicotinic receptor. Analysis of single-channel currents

Bupivacaine and its quaternary derivative, bupivacaine methiodide, were studied on acetylcholine (ACh)-activated single-channel currents recorded in myoballs from neonatal rat muscles using the patch-clamp technique. Under control conditions, the ACh-induced channels had three conductance states, 10, 20, and 33 pS, at a temperature of 10 degrees. The intermediate conductance state (20 pS) was the most prevalent. Moreover, an excessive number of very short events was observed which contributed to a deviation of the channel open-time distribution from a single-exponential function. At 20 degrees, the amplitude of these currents was increased (Q10 = 1.4), and the mean channel open time was decreased (Q10 = 3). Bupivacaine and its quaternary derivative (5-50 microM), when inside the patch micropipette with ACh, caused shortening of the channel open time, but the single-channel conductance remained unchanged at all concentrations studied. In the presence of bupivacaine, there was a loss of voltage dependence of the mean channel open time seen under control conditions; i.e., the shortening of the channel open time was more pronounced at more negative potentials. The plot of the reciprocal of mean channel open time versus bupivacaine concentration was linear. Similar effects were observed when bupivacaine was added to the bathing medium in both cell-attached and inside-out patch conditions, but in this case the onset of the drug action occurred at a later time and its potency was lower. Application of bupivacaine methiodide via the bathing medium after the establishment of the gigaohm seals, however, had no effect on the kinetics of ACh-activated single channels under both patch conditions (cell-attached and inside-out). The patch-clamp results indicated that the charged form of bupivacaine blocks the open state of ACh-activated ionic channels interacting with sites at the extracellular segment of the ACh receptor-ionic channel complex and creating a species with little or no conductance. A sequential model can be used to explain the interactions of these noncompetitive antagonists of the ACh receptor-ionic channel complex with the open channel. This interpretation of the action of bupivacaine and its quaternary analogue as open channel blockers also was reached based on an analysis of macroscopic events in nicotinic synapses of frog muscle.