Patient and Provider Satisfaction with Asynchronous Versus Synchronous Telepsychiatry in Primary Care: A Secondary Mixed-Methods Analysis of a Randomized Controlled Trial

Background: Asynchronous telepsychiatry (ATP) consultations are a novel form of psychiatric consultation. Studies comparing patient and provider satisfaction for ATP with that for synchronous telepsychiatry (STP) do not exist. Methods: This mixed-methods study is a secondary analysis of patients' and primary care providers' (PCPs) satisfaction from a randomized clinical trial of ATP compared with STP. Patients and their PCPs completed satisfaction surveys, and provided unstructured feedback about their experiences with either ATP or STP. Differences in patient satisfaction were assessed using mixed-effects logistic regression models, and the qualitative data were analyzed using thematic analysis with an inductive coding framework. Results: Patient satisfaction overall was high with 84% and 97% of respondents at 6 months reported being somewhat or completely satisfied with ATP and STP, respectively. Patients in the STP group were more likely to report being completely satisfied, to recommend the program to a friend, and to report being comfortable with their care compared with ATP (all p < 0.05). However, there was no difference between the patients in ATP and STP in perceived change in clinical outcomes (p = 0.51). The PCP quantitative data were small, and thus only summarized descriptively. Conclusions: Patients expressed their overall satisfaction with both STP and ATP. Patients in ATP reported more concerns about the process, likely because feedback after ATP was slower than that after STP consultations. PCPs had no apparent preference for STP or ATP, and reported implementing the psychiatrists' recommendations for both groups when such recommendations were made, which supports our previous findings. Trial Registration: ClinicalTrials.gov NCT02084979; https://clinicaltrials.gov/ct2/show/NCT02084979.

Train New Trainers Primary Care Psychiatry Fellowship-Optimizing Delivery of Behavioral Health Care Through Training for Primary Care Providers

OBJECTIVE

To expand and optimize the behavioral health workforce, it is necessary to improve primary care providers' (PCPs) overall knowledge and clinical skills in primary care-based psychiatry. Studies on the effects of postgraduate psychiatric education programs for PCPs on psychiatric knowledge are limited.

METHODS

A total of 251 PCPs completed a 1-year fellowship. Data from program development and evaluation were analyzed for 4 fellowship years (2016-2019). Fellows were surveyed at baseline, midpoint, and postfellowship about mental health stigma, perceived competency, attitudes about psychiatry, satisfaction with current psychiatric knowledge, confidence and comfort to treat psychiatric illnesses, and program satisfaction. Psychiatric knowledge was evaluated at baseline, midpoint, and postfellowship.

RESULTS

Large effects were noted on perceived competency/self-efficacy and confidence in the treatment of common psychiatric disorders encountered in primary care settings. Positive effects were observed on attitudes of mental health stigma, and even more robust effects were found with improvement in psychiatry clinical knowledge. Knowledge improved by 12% at postfellowship (P < .0001). Correlations of the degree of change in attitude with improved psychiatric literacy demonstrated significant relationships with reduction of stigma total score (r = -0.2133, P = .0043), increased willingness (r = 0.1941, P = .0096), and increased positive attitudes (r = 0.1894, P = .0111).

CONCLUSION

Innovative initiatives to improve and expand psychiatric knowledge and clinical skills among those who provide the most behavioral health care (PCPs) can have marked impacts on attitudes toward mental health care delivery, stigma, and competency/self-efficacy. Future studies are necessary to consider the impact of this program on clinical practice pattern outcomes on a larger scale.

Primary Care Physician Adherence to Telepsychiatry Recommendations: Intermediate Outcomes from a Randomized Clinical Trial

Objective: To compare clinical recommendations given by psychiatrists and the adherence to these recommendations by primary care physicians (PCP) following consultations conducted by asynchronous telepsychiatry (ATP) and synchronous telepsychiatry (STP). Materials and Methods: ATP and STP consultations were compared using intermediate data from a randomized clinical trial with adult participant enrollment between April 2014 and December 2017. In both study arms, PCPs received written recommendations from the psychiatrist after each encounter. Independent clinicians reviewed PCP documentation to measure adherence to those recommendations in the 6 months following the baseline consultation. Results: Medical records were reviewed for 645 psychiatrists' consult recommendations; 344 from 61 ATP consultations and 301 from 62 STP consultations. Of those recommendations, 191 (56%) and 173 (58%) were rated fully adherent by two independent raters for ATP and STP, respectively. In a multilevel ordinal logistic regression model adjusted for recommendation type and recommended implementation timing, there was no statistically significant difference in adherence to recommendations for ATP compared with STP (adjusted odds ratio = 0.91, 95% confidence interval = 0.51-1.62). The profiles of recommendation type were comparable between ATP and STP. Conclusions: This is the first PCP adherence study comparing two forms of telemedicine. Although we did not find evidence of a difference between ATP and STP; this study supports the feasibility and acceptability of ATP and STP for the provision of collaborative psychiatric care. Clinical Trial Identifier NCT02084979.

Clinical Outcomes of Asynchronous Versus Synchronous Telepsychiatry in Primary Care: Randomized Controlled Trial

BACKGROUND

Asynchronous telepsychiatry (ATP; delayed-time) consultations are a novel form of psychiatric consultation in primary care settings. Longitudinal studies comparing clinical outcomes for ATP with synchronous telepsychiatry (STP) are lacking.

OBJECTIVE

This study aims to determine the effectiveness of ATP in improving clinical outcomes in English- and Spanish-speaking primary care patients compared with STP, the telepsychiatry usual care method.

METHODS

Overall, 36 primary care physicians from 3 primary care clinics referred a heterogeneous sample of 401 treatment-seeking adult patients with nonurgent psychiatric disorders. A total of 184 (94 ATP and 90 STP) English- and Spanish-speaking participants (36/184, 19.6% Hispanic) were enrolled and randomized, and 160 (80 ATP and 80 STP) of them completed baseline evaluations. Patients were treated by their primary care physicians using a collaborative care model in consultation with the University of California Davis Health telepsychiatrists, who consulted with patients every 6 months for up to 2 years using ATP or STP. Primary outcomes (the clinician-rated Clinical Global Impressions [CGI] scale and the Global Assessment of Functioning [GAF]) and secondary outcomes (patients' self-reported physical and mental health and depression) outcomes were assessed every 6 months.

RESULTS

For clinician-rated primary outcomes, ATP did not promote greater improvement than STP at 6-month follow-up (ATP vs STP, adjusted difference in follow-up at 6 months vs baseline differences for CGI: 0.2, 95% CI -0.2 to 0.6; P=.28; and GAF: -0.6, 95% CI -3.1 to 1.9; P=.66) or 12-month follow-up (ATP vs STP, adjusted difference in follow-up at 12 months vs baseline differences for CGI: 0.4, 95% CI -0.04 to 0.8; P=.07; and GAF: -0.5, 95% CI -3.3 to 2.2; P=.70), but patients in both arms had statistically and clinically significant improvements in both outcomes. There were no significant differences in improvement from baseline between ATP and STP on any patient self-reported ratings at any follow-up (all P values were between .17 and .96). Dropout rates were higher than predicted but similar between the 2 arms. Of those with baseline visits, 46.8% (75/160) did not have a follow-up at 1 year, and 72.7% (107/147) did not have a follow-up at 2 years. No serious adverse events were associated with the intervention.

CONCLUSIONS

This is the first longitudinal study to demonstrate that ATP can improve clinical outcomes in English- and Spanish-speaking primary care patients. Although we did not find evidence that ATP is superior to STP in improving clinical outcomes, it is potentially a key part of stepped mental health interventions available in primary care. ATP presents a possible solution to the workforce shortage of psychiatrists and a strategy for improving existing systems of care.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02084979; https://clinicaltrials.gov/ct2/show/NCT02084979.

Depression

Most psychiatric care is delivered in primary care settings, where depression is the most common presenting psychiatric symptom. Given the high prevalence of depression worldwide and the well-established consequences of untreated depression, the ability of primary care clinicians to effectively diagnose and treat it is critically important. This article offers up-to-date guidance for the diagnosis and treatment of major depressive disorder, including practical considerations for delivering optimal and efficient care for these patients.

Telepsychiatry and other technologies for integrated care: evidence base, best practice models and competencies

Telehealth facilitates integrated, patient-centred care. Synchronous video, telepsychiatry (TP), or telebehavioural health provide outcomes as good as in-person care. It also improves access to care, leverages expertise at a distance, and is effective for education and consultation to primary care. Other technologies on an e-behavioural health spectrum are also useful, like telephone, e-mail, text, and e-consults. This paper briefly organizes these technologies into low, mid and high intensity telehealth models and reviews the evidence base for interventions to primary care, and, specifically, for TP and integrated care (IC). Technology, mobile health, and IC competencies facilitate quality care. TP is a high intensity model and it is the best-studied option. Studies of IC are preliminary, but those with collaborative and consultative care show effectiveness. Low- and mid-intensity technology options like telephone, e-mail, text, and e-consults, may provide better access for patients and more timely provider communication and education. They are also probably more cost-effective and versatile for health system workflow. Research is needed upon all technology models related to IC for adult and paediatric primary care populations. Effective healthcare delivery matches the patients' needs with the model, emphasizes clinician competencies, standardizes interventions, and evaluates outcomes.

An Update on Telepsychiatry and How It Can Leverage Collaborative, Stepped, and Integrated Services to Primary Care

INTRODUCTION

In this era of patient-centered care, telepsychiatry (TP; video or synchronous) provides quality care with outcomes as good as in-person care, facilitates access to care, and leverages a wide range of treatments at a distance.

METHOD

This conceptual review article explores TP as applied to newer models of care (e.g., collaborative, stepped, and integrated care).

RESULTS

The field of psychosomatic medicine (PSM) has developed clinical care models, educates interdisciplinary team members, and provides leadership to clinical teams. PSM is uniquely positioned to steer TP and implement other telebehavioral health care options (e.g., e-mail/telephone, psych/mental health apps) in the future in primary care. Together, PSM and TP provide versatility to health systems by enabling more patient points-of-entry, matching patient needs with provider skills, and helping providers work at the top of their licenses. TP and other technologies make collaborative, stepped, and integrated care less costly and more accessible.

CONCLUSION

Effective health care delivery matches the intensity of the services to the needs of a patient population or clinic, standardizes interventions, and evaluates both process and clinical outcomes. More research is indicated on the application of TP and other technologies to these service delivery models.

Depression

This issue provides a clinical overview of depression, focusing on screening, diagnosis, treatment, and practice improvement. The content of In the Clinic is drawn from the clinical information and education resources of the American College of Physicians (ACP), including MKSAP (Medical Knowledge and Self-Assessment Program). Annals of Internal Medicine editors develop In the Clinic in collaboration with the ACP's Medical Education and Publishing divisions and with the assistance of additional science writers and physician writers.

Integrated Care at the Interface of Psychiatry and Primary Care: Prevention of Cardiovascular Disease

Patients with mental illness, particularly serious mental illness, are more likely to suffer from common disorders without optimal treatment. Changes in preventive practice patterns cannot be fully realized on a large scale until clinicians are trained how to routinely provide this care. Psychiatrists may consider using preventive care strategies in the area of cardiovascular health, as cardiovascular disease is the most common cause of death and disproportionately affects patients with mental illness. At minimum, psychiatrists are well positioned to work collaboratively with primary care providers to address psychopathology that may interfere with adherence to the treatment plan.

General and Child and Adolescent Psychiatry Resident Training in Integrated Care: a Survey of Program Directors

OBJECTIVE

Integrated care models are an evidence-based approach for integrating physical and behavioral health services. The American Association of Directors of Psychiatric Residency Training Integrated Care Task Force sought to describe current practices for providing training in integrated care to general and child and adolescent psychiatry residents.

METHODS

Directors of US general and child and adolescent psychiatric residency training programs were anonymously surveyed to examine current practices in educating their residents in integrated care. Based on themes that emerged from the survey, the authors make recommendations for integrated care education of general and child and adolescent psychiatry residents.

RESULTS

Fifty-two of 197 (26%) general and 36 of 111 (32%) child and adolescent program directors responded. Results demonstrate that a majority of responding general psychiatry (78%) and child and adolescent psychiatry (CAP) (72%) training programs offer integrated care rotations, many of which are electives for senior residents. The Veterans Health Administration (VA) and Federally Qualified Health Centers are common venues for such rotations. Sustainable funding of these rotations is a concern. Fewer than half of programs offer integrated care didactics.

CONCLUSIONS

This report is intended to help program directors consider options for starting or optimizing their own integrated care curricula. Future research should examine the educational value, and the overall value to health care systems, of training in the integrated care model.

Teaching psychiatry residents to work at the interface of mental health and primary care

The authors present examples of programs educating psychiatry residents to work in integrated healthcare settings.

Integrated care: nonfasting screening for cardiovascular risk among individuals taking second-generation antipsychotics

Ischemic heart disease (IHD) is the leading cause of mortality among adults with severe mental illness. Although gains in reducing mortality from IHD through screening, risk reduction, and early intervention have been realized for the general public, rates of recognition and treatment among individuals with mental illness continue to be poor. Obtaining blood samples from patients who have been fasting for eight to 12 hours is challenging for adults with severe mental illness and presents an additional obstacle to screening and treatment. This column outlines newer guidelines for cholesterol and diabetes screening that provide valid alternatives to fasting blood draws, thereby significantly reducing this common barrier to recognition of leading risk factors for IHD.

Preventive medical services use among community mental health patients with severe mental illness:the influence of gender and insurance coverage

INTRODUCTION

This study examines predictors of reduced preventive health service use in patients with severe mental illness by examining psychiatric diagnoses and demographic factors.

METHOD

Of 387 patients approached in 4 community mental health clinics regarding their preventive health services use from January 2005 to May 2007, 234 (60.5%) were interviewed. Of those participants interviewed, 221 had a DSM-IV-TR diagnosis of (1) primary psychotic disorder (schizophrenia or schizoaffective disorder), (2) bipolar disorder, or (3) recurrent major depressive disorder. Psychiatric disorders and demographic factors that predicted high service utilization were analyzed using analysis of variance and χ² tests.

RESULTS

In the linear predictive model, use of preventive services was not statistically different among the 3 diagnostic groups. Participants with primary psychotic disorder used a similar number of preventive services compared to those with bipolar disorder and major depression. Women used more services than men (P < .01), and individuals with health insurance used more than uninsured participants (P < .001).

CONCLUSION

Male gender and not having medical insurance were predictive of lower preventive health service use in this sample of patients with severe mental illness. Further research is needed to replicate these findings and to improve use of preventive health services in people with severe mental illness.

General-medical hospital admissions from a public inpatient psychiatric health facility: a review of medical complications over 30 months

BACKGROUND

Medical comorbidity and mortality disproportionately affect adults with serious mental illness, as compared with the general population.

OBJECTIVE

This study examined the medical diagnoses of patients transferred from a psychiatric health facility to general-medical hospitals.

METHOD

The authors retrospectively reviewed the charts of 81 adult patients admitted to an inpatient psychiatric facility who were subsequently transferred to local general-medical hospitals from January 2005 to June 2007.

RESULTS

Of 6,688 separate inpatient admissions, 81 patients (2.1%) were admitted to general-medical hospitals a total of 93 times, and had 108 admitting medical diagnoses. The leading admission indications were infections (N=33; 34%), electrolyte or nutritional abnormalities (N=12; 11%), and cardiovascular disorders (N=12; 11%). Iatrogenic causes related to psychiatric medications accounted for a small proportion of medical admissions (N=8; 7.5%). Over 90% of the patients had chronic medical disorders, and 80% of the patients had a psychotic or bipolar disorder.

CONCLUSION

Patients with severe mental illness and chronic medical disorders may experience significant acute medical complications during inpatient psychiatric treatment. Given the complex care issues involved, continued vigilance in treating or preventing these conditions is warranted.

Acclimation to decompression sickness in rats

Protection against decompression sickness (DCS) by acclimation to hyperbaric decompression has been hypothesized but never proven. We exposed rats to acclimation dives followed by a stressful "test" dive to determine whether acclimation occurred. Experiments were divided into two phases. Phase 1 rats were exposed to daily acclimation dives of hyperbaric air for 30 min followed by rapid decompression on one of the following regimens: 70 ft of seawater (fsw) for 9 days (L70), 70 fsw for 4 days (S70), 40 fsw for 9 days (L40), 40 fsw for 4 days (S40), or unpressurized sham exposure for 9 days (Control). On the day following the last exposure, all were subjected to a "test" dive (175 fsw, 60 min, rapid decompression). Both L70 and S70 rats had significantly lower incidences of DCS than Control rats (36% and 41% vs. 62%, respectively). DCS incidences for the other regimens were lower than in Control rats but without statistical significance. Phase 2 used the most protective regimen from phase 1 (L70); rats were exposed to L70 or a similar regimen with a less stressful staged decompression. Another group was exposed to a single acclimation dive (70 fsw/30 min) on the day before the test dive. We observed a nonsignificant trend for the rapidly decompressed L70 dives to be more protective than staged decompression dives (44% vs. 51% DCS incidence). The single acclimation dive regimen did not provide protection. We conclude that protection against DCS can be attained with acclimating exposures that do not themselves cause DCS. The deeper acclimation dive regimens (70 fsw) provided the most protection.

Psychiatrists for medically complex patients: bringing value at the physical health and mental health/substance-use disorder interface

BACKGROUND

In their current configuration, traditional reactive consultation-liaison services see a small percentage of the general-hospital patients who could benefit from their care. These services are poorly reimbursed and bring limited value in terms of clinical improvement and reduction in health-service use.

METHOD

The authors examine models of cross-disciplinary, integrated health services that have been shown to promote health and lower cost in medically-complex patients, those with complicated admixtures of physical, mental, social, and health-system difficulties.

CONCLUSION

Psychiatrists who specialize in the treatment of medically-complex patients must now consider a transition from traditional consultation to proactive, value-added programs and bill for services from medical, rather than behavioral, insurance dollars, since the majority of health-enhancement and cost-savings from these programs occur in the medical sector. The authors provide the clinical and financial arguments for such program-creation and the steps that can be taken as psychiatrists for medically-complex patients move to the next generation of interdisciplinary service.

Endothelial-mediated regulation of cerebral microcirculation

Vascular endothelial cells are important not only for maintaining homeostasis, but also in pathogenesis of vascular disorders. Cerebral capillary and microvascular endothelial cells play an active role in maintaining cerebral blood flow, microvascular tone and blood brain barrier functions. Factors produced and released by endothelial cells, other brain cells and circulating blood cells participate in these regulatory functions. In particular, endothelin-1 (ET-1) and nitric oxide (NO) are known to contribute to the functional vascular changes under pathological conditions (e.g., hypertension, arteriosclerosis, and stroke). This report describes the involvement of endothelial cell mediators in the post-ischemic hypoperfusion induced by brain ischemia and in vitro endothelial responses (Ca(2+) mobilization and cytoskeletal rearrangements) to ET-1 and its interactions with NO or 2-AG. The capacity of NO and endocannabinoids to counteract ET-1-induced cerebral capillary and microvascular endothelial responses indicates that they may actively participate in EC function and implicates them in physiological and pathophysiological conditions.

ET-1- and NO-mediated signal transduction pathway in human brain capillary endothelial cells

Previous studies have demonstrated that functional interaction between endothelin (ET)-1 and nitric oxide (NO) involves changes in Ca(2+) mobilization and cytoskeleton in human brain microvascular endothelial cells. The focus of this investigation was to examine the possible existence of analogous interplay between these vasoactive substances and elucidate their signal transduction pathways in human brain capillary endothelial cells. The results indicate that ET-1-stimulated Ca(2+) mobilization in these cells is dose-dependently inhibited by NOR-1 (an NO donor). This inhibition was prevented by ODQ (an inhibitor of guanylyl cyclase) or Rp-8-CPT-cGMPS (an inhibitor of protein kinase G). Treatment of endothelial cells with 8-bromo-cGMP reduced ET-1-induced Ca(2+) mobilization in a manner similar to that observed with NOR-1 treatment. In addition, NOR-1 or cGMP reduced Ca(2+) mobilization induced by mastoparan (an activator of G protein), inositol 1,4,5-trisphosphate, or thapsigargin (an inhibitor of Ca(2+)-ATPase). Interestingly, alterations in endothelial cytoskeleton (actin and vimentin) were associated with these effects. The data indicate for the first time that the cGMP-dependent protein kinase colocalizes with actin. These changes were accompanied by altered levels of phosphorylated vasodilator-stimulated phosphoprotein, which were elevated in endothelial cells incubated with NOR-1 and significantly reduced by ODQ or Rp-8-CPT-cGMPS. The findings indicate a potential mechanism by which the functional interrelationship between ET-1 and NO plays a role in regulating capillary tone, microcirculation, and blood-brain barrier function.

Antioxidant properties of the vasoactive endocannabinoid, 2-arachidonoyl glycerol (2-AG)

Reactive oxygen species (ROS) were shown to play a role in altering blood-brain barrier (BBB) permeability and formation of brain edema induced by trauma and/or ischemia. 2-arachidonoyl glycerol (2-AG), a novel, potent vasodilatory and cytoprotective endocannabinoid has been implicated to act as an antioxidative agent. This study examines: 1) the possible 2-AG modulation of BBB injury and edema formation induced by closed head injury (CHI); and 2) comparable effects between 2-AG and 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TPL), a known antioxidant nitroxide on endothelial Ca2+ and cytoskeletal responses to H2O2 (ROS). 2-AG treatment reduced the CHI-induced increase in BBB permeability and brain edema. The endothelial H2O2-stimulated Ca2+ mobilization and cytoskeleton (vimentin) rearrangement was modified by either 2-AG or TPL. These findings provide evidence of 2-AG antioxidant activity and are consistent with the involvement of ROS in the pathomechanism of CHI-induced BBB injury and brain edema.

Examination of several potential mechanisms for the negative outcome in a clinical stroke trial of enlimomab, a murine anti-human intercellular adhesion molecule-1 antibody: a bedside-to-bench study

BACKGROUND AND PURPOSE

Enlimomab, a murine monoclonal anti-human intercellular adhesion molecule (ICAM)-1 antibody, had a negative outcome in a multicenter acute-stroke trial. We did a bedside-to-bench study in standardized rat stroke models to explore mechanisms for these untoward results.

METHODS

After focal brain ischemia in Wistar rats and spontaneously hypertensive rats (SHR), we administered murine anti-rat ICAM-1 antibody (1A29), subclass-matched murine immunoglobulin (IgG1), or vehicle intravenously. To examine whether rat anti-mouse antibodies were generated against the mouse protein and whether these were deleterious, we sensitized Wistar rats with 1A29 or vehicle 7 days before surgery. Infarct volume, tissue myeloperoxidase activity, neutrophil CD11b expression, and microvascular E-selectin, P-selectin, and ICAM-1 expression were examined 48 hours after surgery. Complement activation was serially assessed for 2 hours after a single injection of either 1A29 or vehicle.

RESULTS

1A29 treatment did not significantly reduce infarct size in either strain. 1A29 sensitization augmented infarct size and generated rat anti-mouse antibodies. Although 1A29 inhibited neutrophil trafficking shown by reduction in brain myeloperoxidase activity, circulating neutrophils were activated and displayed CD11b upregulation. Complement was activated in 1A29-sensitized Wistar rats and 1A29-treated SHR. E-selectin (SHR), endothelial P-selectin (Wistar and SHR), and ICAM-1 (SHR) were upregulated in animals treated with 1A29.

CONCLUSIONS

Administration to rats of a murine antibody preparation against ICAM-1, 1A29, elicits the production of host antibodies against the protein, activation of circulating neutrophils, complement activation, and sustained microvascular activation. These observations provide several possible mechanisms for central nervous system-related clinical deterioration that occurred when Enlimomab was given in acute ischemic stroke.

Adrenergic mediation of TNF alpha-stimulated ICAM-1 expression on human brain microvascular endothelial cells

Adrenergic innervation derived from locus ceruleus has been implicated in regulating BBB permeability and inflammatory responses associated with neurological disorders. This report demonstrates that adrenergic agents attenuate the tumor necrosis factor-alpha (TNF alpha)-induced expression of intercellular adhesion molecule-1 (ICAM-1) on cerebral microvascular endothelial cells (HBMEC) derived from human brains. HBMEC were incubated with isoproterenol (1-10 microM) alone or in the presence of propranolol (10 microM) for 30 min followed by the addition of various concentrations of TNF alpha. ICAM-1 expression on cultured HBMEC was dose-dependently upregulated by TNF alpha. Incubation with isoproterenol significantly reduced levels of ICAM-1 expression indicating the possible involvement of adrenergic agents on ICAM-1 expression. Treatment with propranolol (beta 1/beta 2-adrenergic antagonist) and butoxamine (beta 2-adrenergic antagonist), but not atenolol (beta 1-adrenergic antagonist) reversed this inhibitory effect. Isoproterenol also dose-dependently stimulated cAMP production (assayed by RIA) by HBMEC; propranolol treatment abolished this effect. These data show that the beta 2-adrenergic receptor/cAMP pathway may be partly involved in TNF alpha-stimulated ICAM-1 expression and indicate the possible involvement of adrenergic mediation of capillary function including BBB integrity.

Endothelin-1 and nitric oxide affect human cerebromicrovascular endothelial responses and signal transduction

Endothelium plays a central role in regulating the vascular tone, blood flow and blood brain barrier (BBB) permeability. The experiments presented here examine the mechanisms by which nitric oxide (NO) and endothelin-1 (ET-1) may be involved in these processes. The findings indicate that ET-1-stimulated [Ca2+]i accumulation occurs through activation of ETA receptor. The capacity of NO to affect this response was indicated by results showing: 1) a two-fold increase in ET-1-stimulated [Ca2+]i by L-NAME, the inhibitor of nitric oxide synthase, and 2) a dose-dependent decrease in [Ca2+]i accumulation by pretreatment with Nor-1 (NO donor). Abrogation of this Nor-1 effect by ODQ (an inhibitor of guanylyl cyclase) or Rp-8-pCPT-cGMPS (an inhibitor of protein kinase G) and inhibition of ET-1 stimulated intracellular Ca2+ accumulation by 8-bromo-cGMP (a permeable, analog of cGMP) substantiate the involvement of interplay between ET-1 and NO in [Ca2+]i accumulation in HBMEC. ET-1 treatment also increased thickness of F-actin cytoskeletal filaments in HBMEC. This effect was attenuated by pretreatment with NO; NO also rarefied F-actin filaments in control cultures. The findings support a linkage between NO and ET-1 in regulating microvascular tone, microcirculation and BBB permeability and indicate a role for cGMP/cGMP protein kinase system and cytoskeletal changes in responses of HBMEC.

Human brain capillary endothelium: 2-arachidonoglycerol (endocannabinoid) interacts with endothelin-1

In brain, the regulatory mechanism of the endothelial reactivity to nitric oxide and endothelin-1 may involve Ca(2+), cytoskeleton, and vasodilator-stimulated phosphoprotein changes mediated by the cGMP/cGMP kinase system.(1) Endothelium of human brain capillaries or microvessels is used to examine the interplay of endothelin-1 with the putative vasorelaxant 2-arachidonoyl glycerol, an endogenous cannabimimetic derivative of arachidonic acid. This study demonstrates that 2-arachidonoyl glycerol counteracts Ca(2+) mobilization and cytoskeleton rearrangement induced by endothelin-1. This event is independent of nitric oxide, cyclooxygenase, and lipoxygenase and is mediated in part by cannabimimetic CB1 receptor, G protein, phosphoinositol signal transduction pathway, and Ca(2+)-activated K(+) channels. The induced rearrangements of cellular cytoskeleton (actin or vimentin) are partly prevented by inhibition of protein kinase C or high levels of potassium chloride. The 2-arachidonoyl glycerol-induced phosphorylation of vasodilator-stimulated phosphoprotein is mediated by cAMP. These findings suggest that 2-arachidonoyl glycerol may contribute to the regulation of cerebral capillary and microvascular function.

Differential expression of HSC73 and HSP72 mRNA and proteins between young and adult gerbils after transient cerebral ischemia: relation to neuronal vulnerability

This study presents a quantitative comparison of the time courses and regional distribution of both constitutive HSC73 and inducible HSP72 mRNA expression and their respective encoded proteins between young (3-week-old) and adult (3-month-old) gerbil hippocampus after transient global ischemia. The constitutive expression of HSC73 mRNA and protein in the hippocampus of the young sham-operated gerbils was significantly higher than in the adults. The HSC73 mRNA expression after ischemia in the CA1 layer of young gerbils was greater than in adult gerbils. HSC73 immunoreactivity was not significantly changed after ischemia-reperfusion in adult hippocampus, whereas it decreased in young gerbils. Ischemia-reperfusion led to induction of HSP72 mRNA expression throughout the hippocampus of both young and adult gerbils. HSP72 mRNA induction was more intense and sustained in the CA1 subfield of young gerbils; this was associated with a marked induction of HSP72 proteins and neuronal survival. The transient expression of HSP72 mRNA in the CA1 layer of adult gerbils was not associated with a subsequent synthesis of HSP72 protein but was linked to neuronal loss. Expression of HSP72 mRNA was shifted to an earlier period of reflow in CA3 and dentate gyrus (DG) subfields of young animals. These findings suggest that the induction of both HSP72 mRNA and proteins in the CA1 pyramidal neurons of young gerbils, as well as the higher constitutive expression of HSC73, may partially contribute to higher neuronal resistance of young animals to transient cerebral ischemia.

Endothelin receptor antagonist preserves microvascular perfusion and reduces ischemic brain damage following permanent focal ischemia

Synthesis and release of the potent vasoconstrictor peptide endothelin-1 (ET-1) increases following cerebral ischemia and has previously been shown to mediate the delayed hypoperfusion associated with transient global ischemia. In this study we assessed the impact of ET-1 on perfusion and infarct volume in a focal model of cerebral ischemia by use of the selective ET(A) receptor antagonist Ro 61-1790 (affinity for ET(A) receptor 1000 fold greater than ETB receptor). Control rats subjected to permanent middle cerebral artery occlusion (MCAO) showed extensive reductions in microvascular perfusion 4 h post-MCAO that were significantly attenuated by Ro 61-1790 pretreatment (10 mg/kg, i.v.). Ro 61-1790 concomitantly and significantly reduced the ischemic lesion volume in the same animals. This effect was maintained 24 h post-MCAO providing that the animals received additional i.v. injections of 5 mg/kg Ro 61-1790 at 5 h and 8 h after MCAO. These findings demonstrate that ET(A) receptor antagonism partially preserves tissue perfusion following focal ischemia and that this effect is associated with significant neuroprotection. The results also support the hypothesis that vasoactive mediators, and ET-1 in particular, are important contributors to the pathogenesis of cerebral ischemic injury.

[Pathophysiologic effects of nitric oxide (NO) and endothelin-1 in global cerebral ischemia in an animal model--an overview]

These studies were performed in an attempt to clarify some of the pathophysiologic mechanisms which occur during and after global ischemia. Both nitric oxide and endothelin were demonstrated in gerbils to participate in responses to ischemia. It was shown that endogenous nitric oxide influences early postischemic reperfusion, systemic blood pressure and postischemic dopamine metabolism. Furthermore, the results indicated that nitric oxide played a role in dopamine release and that preischemic intracerebral nitric oxide formation significantly decreased ischemic dopamine release. In addition, ischemic release of endothelin-1 was detected; participation of nitric oxide in this release was observed. Further indication of functional interactions between nitric oxide and endothelin-1 in postischemic reperfusion were indicated by observations that endothelin-1 antagonists inhibited early hypoperfusion caused by Nitro-L-arginin and late hypoperfusion caused by endogenous endothelin-1. Nitric oxide was shown to decrease edema formation during the early postischemic period but contribute to edema formation during the late postischemic period. The findings indicate the importance of nitric oxide in stroke and ischemia.

Nitric oxide modulates endothelin 1-induced Ca2+ mobilization and cytoskeletal F-actin filaments in human cerebromicrovascular endothelial cells

A functional interrelation between nitric oxide (NO), the endothelial-derived vasodilating factor, and endothelin 1 (ET-1), the potent vasoconstrictive peptide, was investigated in microvascular endothelium of human brain. Nor-1 dose-dependently decreased the ET-1-stimulated mobilization of Ca2+. This response was mimicked with cGMP and abrogated by inhibitors of guanylyl cyclase or cGMP-dependent protein kinase G. These findings indicate that NO and ET-1 interactions involved in modulation of intracellular Ca2+ are mediated by cGMP/protein kinase G. In addition, Nor-1-mediated effects were associated with rearrangements of cytoskeleton F-actin filaments. The results suggest mechanisms by which NO-ET-1 interactions may contribute to regulation of microvascular function.

Human brain capillary endothelium: modulation of K+ efflux and K+, Ca2+ uptake by endothelin

This report describes K+ efflux, K+ and Ca2+ uptake responses to endothelins (ET-1 and ET-3) in cultured endothelium derived from capillaries of human brain (HBEC). ET-1 dose dependently increased K+ efflux, K+ and Ca2+ uptake in these cells. ET-1 stimulated K+ efflux occurred prior to that of K+ uptake. ET-3 was ineffective. The main contributor to the ET-1 induced K+ uptake was ouabain but not bumetanide-sensitive (Na+-K+-ATPase and Na+-K+-Cl- cotransport activity, respectively). All tested paradigms of ET-1 effects in HBEC were inhibited by selective antagonist of ET(A) but not ET(B) receptors and inhibitors of phospholipase C and receptor-operated Ca2+ channels. Activation of protein kinase C (PKC) decreased whereas inhibition of PKC increased the ET-1 stimulated K+ efflux, K+ and Ca2+ uptake in HBEC. The results indicate that ET-1 affects the HBEC ionic transport systems through activation of ET(A) receptors linked to PLC and modulated by intracellular Ca2+ mobilization and PKC.

Increased endothelial expression of intercellular adhesion molecule-1 in symptomatic versus asymptomatic human carotid atherosclerotic plaque

BACKGROUND AND PURPOSE

The mechanisms that cause carotid atherosclerotic plaque to become symptomatic remain unclear. Evidence suggests that mediators of inflammation are not only instrumental in the formation of plaque but may also be involved in the rapid progression of atheromatous lesions leading to plaque fissuring, endothelial injury, and intraluminal thrombosis. Our goal is to determine whether intercellular adhesion molecule-1 (ICAM-1), a known component of the inflammatory pathway, is preferentially expressed on symptomatic versus asymptomatic carotid plaques.

METHODS

Carotid plaques from symptomatic (n = 25) and asymptomatic (n = 17) patients undergoing carotid endarterectomy with lesions involving >60% stenosis were snap-frozen at the time of surgery. Immunofluorescence studies were performed to measure the percentage of luminal endothelial surface that expressed ICAM-1. The relationships of stroke risk factors, white blood cell count, percent stenosis, and soluble ICAM-1 (sICAM-1) plasma levels to endothelial ICAM-1 expression were investigated.

RESULTS

An increased expression of ICAM-1 was found in the high-grade regions of symptomatic (29.5%+/-2.4%, mean+/-SEM) versus asymptomatic (15.7%+/-2.7%, mean+/-SEM) plaques (P=0.002) and in the high-grade versus the low-grade region of symptomatic plaques (29.5+/-2.4, mean+/-SEM, versus 8.9+/-1.6; P<0.001). Plasma sICAM-1 levels were not predictive of symptomatic disease, and no significant correlation between risk factor exposure and endothelial ICAM-1 expression was found.

CONCLUSIONS

An elevation in ICAM-1 expression in symptomatic versus asymptomatic plaque suggests that mediators of inflammation are involved in the conversion of carotid plaque to a symptomatic state. The data also suggest a differential expression of ICAM-1, with a greater expression found in the high-grade region than in the low-grade region of the plaque specimen.

Hypoxia modulates free radical formation in brain microvascular endothelium

Although free radical species (ROS; i.e., .O2-. .OH.H2O2) among other mediators, may be involved in altering the blood-brain barrier (BBB), little is known about the endogenous ability of cerebromicrovascular endothelium to generate ROS. This study examines the capacity of rat endothelial cells (RBEC) to produce ROS in normoxia and hypoxia/reoxygenation. Cultured RBEC were exposed to an oxygen-depleted atmosphere (containing 95% N2 and 5% CO2) for 4 hr at 37 degrees C and air (10 min) at room temperature to simulate "ischemia/reperfusion". Nitroblue tetrazolium (NBT) reduction [formation of nitroblue formazan (NBF)] served as a marker for the production of ROS. The release of lactate dehydrogenase (LDH) and [3H]arachidonic acid (AA) was used to assess cellular integrity. RBEC exposed to hypoxia/reoxygenation produced up to 59% greater NBF formation than controls without affecting the LDH or AA release. The production of ROS was calcium-dependent and not affected by AA or its metabolites. The findings indicate that the RBEC can produce superoxide dismutase (SOD)-inhibitable ROS which are augmented by hypoxia/reoxygenation. It is suggested that in vivo cerebromicrovascular endothelium may contribute to the formation of ROS and play a role in ischemic brain edema.

The effect of nitric oxide inhibition on ischemic brain edema

The involvement of nitric oxide (NO) in the development of ischemic cytotoxic edema was investigated by inhibiting nitric oxide synthase (NOS) activity with N omega-nitro-L-arginine (NLA). Bilateral carotid artery occlusion (15 min) alone or with release (15 and 60 min) served as a model for edema induction. NLA, N omega-nitro-D-arginine methyl ester (D-NAME) or Ringer's solution were administered 4 hr prior to ischemia or sham operation. Treatment with a stable nitroxide radical, 4-hydroxy-2,2, 6,6-tetramethylpiperidine-L-oxyl (TPL), was used to assess free radical involvement in edema. Accumulation of tissue water was evaluated by measuring specific gravity (SG) of brain cortex and histological examination. There was a greater reduction of cortical SG in early reperfusion (15 min) and a lesser decrease in SG (60 min later) in NLA-than in D-NAME- or Ringer's-treated gerbils. The NLA effect was confirmed by histological examination of the brain tissue. TPL treatment (pre- and postischemic) ameliorated the formation of edema to the same degree as NLA. The findings indicate a biphasic NLA modulation of cytotoxic edema most likely mediated through absence or presence of NO-derived free radicals.

The effect of endothelins on ion transport systems in cultured rat brain capillary endothelial cells

Brain capillary endothelial cells regulate the movement of ions and water across the blood-brain barrier via specific ion transport systems. Disturbances in these ion transport systems are involved in the formation of ischemic brain edema. This study describes the effects of endothelins (i.e., ET-1 and ET-3) on ion transport systems in cultured rat brain capillary endothelial cells using 86Rb+ and 22Na+ as markers for K+ and Na+, respectively. ET-1 stimulated K+ uptake and efflux with EC50 values of 0.6 nM and 0.5 nM, respectively. The potencies of ET-3 on these responses were considerably lower. Both ET-1 and ET-3 stimulated Na+ uptake through a Na+/H+ exchange system with similar potencies (i.e., EC50 = 0.80 nM and 1.89 nM, respectively). ET-stimulated K+ uptake, K+ efflux, and Na+ uptake activities were all inhibited by BQ123 (selective ETA receptor antagonist). ET-1 stimulated K+ uptake and efflux, in contrast to Na+ uptake, were also reduced by protein kinase C inhibitors and by an intracellular Ca2+ chelator. The results suggest that ETs can affect the activities of ion and water transport at the blood-brain barrier through different signal transduction mechanisms.

Effects of plasma from hibernating ground squirrels on monocyte-endothelial cell adhesive interactions

Adhesion and subsequent penetration of leukocytes into central nervous system ischemic tissue proceeds via a coordinated inflammatory mechanism involving adhesion molecules at the blood-endothelium interface. Mammalian hibernation is a state of natural tolerance to severely reduced blood flow-oxygen delivery (i.e., ischemia). Hibernating thirteen-lined ground squirrels were investigated in an attempt to identify factors responsible for regulating this tolerance. Since leukocytopenia is closely associated with entrance into hibernation, the role of leukocyte adhesion to endothelium in this phenomenon was examined. Intercellular adhesion molecule-1 (ICAM-1) is expressed by endothelium and regulates interactions with circulating leukocytes that may result in margination or extravasation. ICAM-1 expression by rat cerebral microvascular endothelial cells (EC) cultured with plasma from hibernating (HP) or nonhibernating (NHP) thirteen-lined ground squirrels was dose dependently increased by HP and, to a lesser extent, by NHP. Treatment of EC with HP coincidentally induced significantly greater increases in monocyte adhesion to EC (37.2%) than were observed with NHP (23.9%). Study of the effects of HP and NHP on monocyte adhesion to EC may identify mechanisms responsible for ischemic tolerance in hibernators and could lead to the development of novel therapeutic approaches to the treatment of stroke.

Functional characterization of endothelin receptors on cultured brain capillary endothelial cells of the rat

This report describes the effects of endothelins (ET-1 and ET-3) on ion transport systems expressed on cultured rat brain capillary endothelial cells (RBEC) and includes investigation of pharmacological properties of ET receptors, their reactivity and induction of signal transduction pathways. ET-1 stimulated IP3 formation and Ca2+ uptake with half-maximal effective concentrations (EC50) of 0.68 and 0.93 nM, respectively; the effects of ET-3 on these responses were much weaker. ET-1-stimulated IP3 formation and Ca2+ uptake were inhibited by an ETA antagonist (BQ123) and a phospholipase C (PLC) inhibitor (U73122), indicating the presence of ETA receptors coupled to PLC. ET-1 stimulated K+ efflux (through a quinine-sensitive mechanism) and K+ uptake (through both ouabain-sensitive and bumetanide-sensitive mechanisms) with EC50 of 0.59 and 0.68 nM, respectively. The potencies of ET-3 on these responses were considerably lower than those of ET-1. By contrast, ET-1 or ET-3 stimulated Na+ uptake with similarly high potencies (EC50 = 0.80 and 1.89 nM, respectively) through EIPA (a Na+/H+ exchange inhibitor)-sensitive mechanisms. ET-stimulated K+ efflux, K+ uptake and Na+ uptake activities were all inhibited by BQ123 (but not by BQ788), suggesting the involvement of ETA (and not ETB) receptors in all these responses. ET-1 stimulated K+ uptake and efflux were inhibited by either U73122 or an intracellular Ca2+ chelator, suggesting that these two responses were mediated via PLC. In contrast, ET stimulation of Na+ uptake was unaffected by PLC inhibition or intracellular Ca2+ chelation. These data suggest the presence of two distinct subtypes of ETA receptors on RBEC; one appears to be a typical ETA receptor which is coupled to PLC and has higher binding affinity for ET-1 than ET-3. The other (ETA-like) receptor is similarly activated by ET-1 and ET-3 with high potencies but is independent of PLC. This possibility was further confirmed by the [125I]ET-1 binding studies demonstrating the presence of high- and low-affinity ET-3 binding sites.

Immunologic tolerance to myelin basic protein decreases stroke size after transient focal cerebral ischemia

Immune mechanisms contribute to cerebral ischemic injury. Therapeutic immunosuppressive options are limited due to systemic side effects. We attempted to achieve immunosuppression in the brain through oral tolerance to myelin basic protein (MBP). Lewis rats were fed low-dose bovine MBP or ovalbumin (1 mg, five times) before 3 h of middle cerebral artery occlusion (MCAO). A third group of animals was sensitized to MBP but did not survive the post-stroke period. Infarct size at 24 and 96 h after ischemia was significantly less in tolerized animals. Tolerance to MBP was confirmed in vivo by a decrease in delayed-type hypersensitivity to MBP. Systemic immune responses, characterized in vitro by spleen cell proliferation to Con A, lipopolysaccharide, and MBP, again confirmed antigen-specific immunologic tolerance. Immunohistochemistry revealed transforming growth factor beta1 production by T cells in the brains of tolerized but not control animals. Systemic transforming growth factor beta1 levels were equivalent in both groups. Corticosterone levels 24 h after surgery were elevated in all sham-operated animals and ischemic control animals but not in ischemic tolerized animals. These results demonstrate that antigen-specific modulation of the immune response decreases infarct size after focal cerebral ischemia and that sensitization to the same antigen may actually worsen outcome.

Functional properties of cultured endothelial cells derived from large microvessels of human brain

This report describes the fractional separation of microvessels from human brain for establishment of segmentally derived endothelial cell (EC) cultures. The investigation comprised evaluation of media constituents and purity of the cell culture and focused on functional biochemical characterization of endothelium derived from large microvessels (EC) Cells contained endothelial marker factor VIII (von Willebrand antigen), secreted endothelin-1 (ET-1) and prostaglandins, and took up 86Rb+ as a measure of K+. Exogenous ET-1 stimulated phosphatidylinositol hydrolysis and K+ uptake; BQ-123 (selective ETA receptor antagonist) but not IRL-1038 or BQ-788 (selective ETB receptor antagonists) inhibited both. Ouabain (inhibitor of Na(+)-K(+)-ATPase) and bumetanide (inhibitor of Na(+)-K(+)-Cl- cotransport) reduced (74-80 and 20-40%, respectively) the ET-1-stimulated K+ uptake. Staurosporine [protein kinase C (PKC) inhibitor] selectively reduced Na(+)-K(+)-Cl- cotransport, whereas verapamil but not nifedipine (L-type voltage-dependent Ca2+ channel blockers) decreased Na(+)-K(+)-ATPase activity induced by ET-1. Phorbol 12-myristate 13-acetate (PMA; activator of PKC) stimulated K+ uptake, which was only decreased with bumetanide. N-ethylisopropylamiloride (inhibitor of Na+/H+ exchange) reduced the ET-1-stimulated but not the PMA-induced K+ uptake. Results indicate that phosphatidylinositol hydrolysis and ion transport systems in large microvascular EC are stimulated by ET-1 through activation of ETA receptors. The findings also suggest that the ET-1-stimulated Na(+)-K(+)-ATPase activity, in contrast to Na(+)-K(+)-Cl- cotransport, is not mediated by PKC. In addition, the data suggest a linkage between Na(+)-K(+)-ATPase activity and Na+/H+ exchange.

Na(+)-K(+)-Cl- cotransport system in brain capillary endothelial cells: response to endothelin and hypoxia

Effect of endothelin-1 and chemically induced hypoxia on Na(+)-K(+)-Cl- cotransport activity in cultured rat brain capillary endothelial cells was examined by using 86Rb+ as a tracer for K+; bumetanide-sensitive K+ uptake was defined as Na(+)-K(+)-Cl- cotransport activity. Endothelin-1, phorbol 12-myristate 13-acetate (PMA), or thapsigargin increased Na(+)-K(+)-Cl- cotransport activity. A protein kinase C inhibitor, bisindolylmaleimide, inhibited PMA- and endothelin-1- (but not thapsigargin-) induced Na(+)-K(+)-Cl- cotransport activity, indicating the presence of both protein kinase C-dependent regulatory mechanisms and protein kinase C-independent mechanisms which involve intracellular Ca2+. Oligomycin, sodium azide, or antimycin A increased Na(+)-K(+)-Cl- cotransport activity by 80-200%. Oligomycin-induced Na(+)-K(+)-Cl- cotransport activity was reduced by an intracellular Ca2+ chelator (BAPTA/AM) but not affected by bisindolylmaleimide, suggesting the involvement of intracellular Ca2+, and not protein kinase C, in hypoxia-induced Na(+)-K(+)-Cl- cotransport activity.

Decreased calcium accumulation in isolated nerve endings during hibernation in ground squirrels

Resting and depolarization-induced 45CaCl2 accumulation was compared for synaptosomes isolated from hibernating and nonhibernating ground squirrels. Channel subtype antagonists were used to identify the active voltage-sensitive calcium channel subtypes in these preparations. There was significantly less 45Ca2+ accumulation in synaptosomes isolated from hibernating as compared to cold-adapted nonhibernating ground squirrels in both basal (p < 0.005) and depolarizing (p < 0.03) media over a 30 sec to 5 min incubation period. The elevation in 45Ca2+ accumulation triggered by K+ depolarization was blocked by 50 microM CdCl2, 1 microM omega-conotoxin MVIIC or 1 microM omega-agatoxin IVA. Inhibition was not observed with 1 microM nifedipine or with 1 microM omega-conotoxin GVIA. These results suggest that hibernation is associated with reduced presynaptic 45Ca2+ conductance via voltage-sensitive channels with a pharmacological sensitivity that is different from the established L-, N-, and P-types in other systems but share features of the recently described Q-type calcium channel. This decrease may reflect a cellular adaptation that helps confer tolerance to the near total cerebral ischemia associated with hibernation.

Cerebral postischemic hypoperfusion is mediated by ETA receptors

Effect of ETA-receptor antagonist, BQ123, on postischemic hypoperfusion in the presence or absence of nitric oxide synthetase inhibitor, N omega-nitro-L-arginine (NLA), was investigated in Mongolian gerbils. BQ123 given prior to ischemia reversed the early incomplete recovery of cerebral blood flow observed with NLA without affecting the late postischemic hypoperfusion. Additional postischemic administration of BQ123 also reversed (P < 0.01) the late postischemic hypoperfusion seen in NLA-, N omega-nitro-D-arginine methyl ester- or Ringer's-treated animals.

Effect of hypoxia on Na(+)-K(+)-Cl- cotransport in cultured brain capillary endothelial cells of the rat

The effect of hypoxia on Na+, K(+)-ATPase and Na(+)-K(+)-Cl- cotransport activity in cultured rat brain capillary endothelial cells (RBECs) was investigated by measuring 86Rb+ uptake as a tracer for K+. RBECs expressed both Na+, K(+)-ATPase and Na(+)-K(+)-Cl- cotransport activity (4.6 and 5.5 nmol/mg of protein/min, respectively). Hypoxia (24 h) decreased cellular ATP content by 43.5% and reduced Na+, K(+)-ATPase activity by 38.9%, whereas it significantly increased Na(+)-K(+)-Cl- cotransport activity by 49.1% in RBECs. To clarify further the mechanism responsible for these observations, the effect of oligomycin-induced ATP depletion on these ion transport systems was examined. Exposure of RBECs to oligomycin led to a time-dependent decrease of cellular ATP content (by approximately 65%) along with a complete inhibition of Na+, K(+)-ATPase and a coordinated increase of Na(+)-K(+)-Cl- cotransport activity (up to 100% above control values). Oligomycin augmentation of Na(+)-K(+)-Cl- cotransport activity was not observed in the presence of 2-deoxy-D-glucose (a competitive inhibitor of glucose transport and glycolysis) or in the absence of glucose. These results strongly suggest that under hypoxic conditions when Na+, K(+)-ATPase activity is reduced, RBECs have the ability to increase K+ uptake through Na(+)-K(+)-Cl-cotransport.