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1.
J Trauma Acute Care Surg ; 95(2S Suppl 1): S41-S49, 2023 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-37199516

RESUMO

BACKGROUND: Maritime activities have been associated with unique dangers to civilian and military sailors. We performed a retrospective cohort study analyzing injury mechanisms and clinical outcomes of casualties onboard US naval ships to determine common injury mechanisms, trends, and outcomes. We hypothesized there would be a downward trend of injuries and fatalities on US naval ships during the study period. METHODS: All mishaps recorded by the Naval Safety Command aboard active service US naval ships from 1970 through 2020 were reviewed. Only mishaps resulting in injury or fatality were included. Over time, injury mechanisms and casualty incidence rates were trended and compared based on medical capabilities. Ships without surgical capabilities were categorized as Role 1, and those with surgical capabilities as Role 2. RESULTS: There were a total of 3,127 casualties identified and analyzed, with 1,048 fatalities and 2,079 injuries. The injury mechanisms associated with the highest mortality included electrocution, blunt head trauma, fall from height, man overboard, and explosion. There was a decrease in the trend of mishaps resulting in casualties, fatalities, and injuries over the 50-year study period. The mortality rate for select severe injury mechanisms was higher on Role 1 capable platforms, compared with Role 2 (0.334 vs. 0.250, p < 0.05). CONCLUSION: Casualty incidences decreased over 50 years. However, mortality still remains high for certain mechanisms no matter the operational platform. Furthermore, Role 1 capable vessels have a higher overall mortality rate for severe injuries compared with Role 2. The authors propose training, process improvement, and technology-related solutions to improve outcomes on Role 1 capable naval vessels. LEVEL OF EVIDENCE: Prognostic and Epidemiological; Level IV.


Assuntos
Militares , Navios , Masculino , Humanos , Estudos Retrospectivos , Incidência , Acidentes por Quedas
2.
Eur J Trauma Emerg Surg ; 49(2): 795-801, 2023 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-36273349

RESUMO

PURPOSE: Resuscitative endovascular balloon occlusion of the aorta (REBOA) is a well-validated method for the control of noncompressible truncal hemorrhage. In lower resource or battlefield settings, the need for arterial line setup and monitoring is problematic and potentially prohibitive. We sought to evaluate the accuracy and precision of a miniaturized portable device (Centurion COMPASS®) versus standard arterial pressure monitoring using standard ER-REBOA and partial REBOA (pREBOA) as a high-fidelity and space-/time-conserving alternative. METHODS: A total of 40 swine underwent a four-phase validation/precision study (each phase using five ER-REBOAs and five pREBOAs). Phases I/II evaluated accuracy with full and pREBOA in uninjured animals. Phases III/IV duplicated the previous phases but in a severe hemorrhagic shock model. Carotid and femoral pressures were monitored with both intra-arterial pressure systems and the COMPASS® device. The vascular flow was measured by aortic flow probes. Correlation and Bland-Altman analysis were performed. RESULTS: There was a strong correlation in accuracy testing of proximal and distal COMPASS® devices compared to standard intra-arterial pressure monitoring (r = 0.94, 0.8; p < 0.005) as well as during precision testing (r = 0.98, 0.89 p < 0.005) in the uninjured phases. Similar accuracy and reliability were demonstrated in hemorrhagic shock, with a strong correlation for the proximal and distal COMPASS® devices (r = 0.98, 0.97; p < 0.005), as well as during precision testing (r = 0.99, 0.95; p < 0.005) in both full and pREBOA scenarios. Bland-Altman analysis showed extremely low bias between the COMPASS® and arterial line for both proximal (bias = 1.9) and distal (bias = 0.8) pressure measurements. CONCLUSION: The COMPASS® provides accurate and precise pressure measurements during standard and partial REBOA in both uninjured and shock conditions. This device may help extend and enhance capability in any low-resource/battlefield settings, or even eliminate the need for standard intra-arterial invasive pressure monitoring and external setup.


Assuntos
Oclusão com Balão , Procedimentos Endovasculares , Choque Hemorrágico , Suínos , Animais , Choque Hemorrágico/terapia , Pressão Arterial , Reprodutibilidade dos Testes , Modelos Animais de Doenças , Aorta , Oclusão com Balão/métodos , Ressuscitação/métodos , Procedimentos Endovasculares/métodos
3.
J Am Coll Surg ; 235(3): 430-435, 2022 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-35972161

RESUMO

BACKGROUND: Although trauma centers represent an integral part of healthcare in the US, characterization of their financial vulnerability has not been reported. We sought to characterize the financial health and vulnerability among California trauma centers and identify factors associated with high and low vulnerability. STUDY DESIGN: The RAND Hospital Data financial dataset was used to evaluate all American College of Surgeons (ACS)-verified trauma centers in California. Financial vulnerability of each center was calculated using 6 metrics to calculate a composite Financial Vulnerability Score (FVS). Tertiles of the FVS were generated to classify trauma centers as high, medium, or low financial vulnerability. Hospital characteristics were also analyzed and compared. RESULTS: Forty-seven ACS trauma centers were identified. Nine were Level I, 27 were Level II, and 8 were Level III. Level I centers encompassed the greatest proportion of the high FVS tier (44%), whereas Level II and III centers were the most likely to be in the middle and lower tiers, respectively (44%; 63%). Lower FVS centers had greater asset:liability ratios, operating margins, and days cash on hand compared with the 2 higher tiers, whereas high FVS centers showed a greater proportion of uncompensated care, outpatient share rates, outpatient surgeries, and longer days in net accounts. Lower FVS centers were more likely to be teaching hospitals and members of a larger corporate entity. CONCLUSION: Many ACS trauma centers are at moderate/high risk for financial vulnerability and disparate impacts of stressor events, and the FVS may represent a novel metric that could be used at the local or statewide level.


Assuntos
Cirurgiões , Centros de Traumatologia , Mortalidade Hospitalar , Hospitais de Ensino , Humanos , Estados Unidos
4.
Am Surg ; 88(10): 2440-2444, 2022 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-35549732

RESUMO

BACKGROUND: Trauma patients are resource intensive, requiring a variety of medical and procedural interventions during hospitalization. These expenses often label trauma care as "high cost" based on gross hospital charges. We hypothesized that a financial metric built on actual costs and clinically relevant trauma patient cohorts would demonstrate a lower true cost of trauma care than the standardly reported gross hospital charges. METHODS: We examined all trauma patients (≥16 yr) treated in 2017 from a single institution and matched them to the institution's detailed financial accounting data. The organization's Financial Operations Division is uniquely able to allocate total operating costs across patient encounters to include medications, procedures, and salaries/fees from medical professionals and administrators. Patient subgroups were identified by Trauma Quality Improvement Program (TQIP) criteria for cost comparisons. RESULTS: Overall median cost per patient was $6,544 [IQR $4,975-14,532] for 2,548 patients. The median cost per patient increased with Injury Severity Score (ISS) ranging from $5,457(ISS ≤ 7) to $34,898(ISS ≥ 21), each accompanied by an average 548% increase in gross charges. Costs also varied widely from $13,498 [IQR $8,247-26,254] to $45,759 [IQR $22,186-113,993] across TQIP patient cohorts. Of the total cost, 91% was attributed to personnel alone. DISCUSSION: Measuring the true cost of trauma care is feasible. As hypothesized, the true cost of trauma care is lower than charges. True cost increased with injury severity with variable cost across subgroups. Non-physician staff and administration are the largest component of the cost of trauma care.


Assuntos
Preços Hospitalares , Centros de Traumatologia , Custos Hospitalares , Hospitalização , Humanos , Escala de Gravidade do Ferimento , Tempo de Internação
5.
Eur J Trauma Emerg Surg ; 48(1): 107-112, 2022 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-34775508

RESUMO

BACKGROUND: The relationship between surgical management of adhesive small bowel obstruction (ASBO) and hospital teaching status is not well known. We sought to elucidate the association between hospital teaching status and clinical metrics for ASBO. METHODS: Using the 2007-2017 California Office of Statewide Health Planning and Development database, we identified adult ASBO patients hospitalized for surgical intervention. Hospital teaching status was categorized as major teaching (MajT), minor teaching (MinT), and non-teaching (NT). Cox proportional hazards modeling was used to evaluate risk of death and other adverse outcomes. RESULTS: Of 25,047 admissions, 15.4% were at MajT, 32.0% at MinT, and 52.6% at NT; 2.9% died. Patients at MajT had longer overall hospital stays (HLOS) than those at MinT or NT (median days 9 vs. 8 vs. 8; p = 0.005), longer post-ASBO procedure HLOS (median days 7 vs. 6 vs. 6; p = 0.0001) and higher rates of small bowel resection (27.1% vs. 21.7% vs. 21.7%; p < 0.0001). Mean time to first surgery at MajT was 3.3 days compared with 2.6 days (p = 0.004) at MinT and NT. Compared with patients at NT, those at MajT were significantly less likely to die (HR 0.62, p < 0.0001), develop pneumonia (HR 0.57, p = 0.001), or experience adverse discharge disposition (HR 0.79, p < 0.0001). CONCLUSION: Mortality and morbidity of ASBO surgery were reduced at MajT; however, time to surgery, HLOS, and rate of small bowel resection were greater. These findings may guide improvements in the management of ASBO patients.


Assuntos
Adesivos , Obstrução Intestinal , Adulto , Humanos , Obstrução Intestinal/cirurgia , Intestino Delgado/cirurgia , Estudos Retrospectivos , Aderências Teciduais , Resultado do Tratamento
6.
J Trauma Acute Care Surg ; 91(5): 829-833, 2021 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-34695059

RESUMO

BACKGROUND: Trauma care is associated with unplanned readmissions, which may occur at facilities other than the index treatment facility. This "fragmentation of care" may be associated with adverse outcomes. We evaluated a statewide database that includes readmissions to analyze the incidence and impact of FC. METHODS: The California Office of Statewide Health Planning and Development patient discharge data set was evaluated for calendar years 2016 to 2018. Patients 15 years or older diagnosed with blunt abdominal solid organ injury during the index admission were identified. Readmissions were evaluated postdischarge at 1, 3, and 6 months. Patients readmitted within 6 months to a facility other than the index admission facility (fragmented care [FC]) were compared with those readmitted to their index admission facility (non-FC). Logistic regression modeling was used to evaluate risk of FC. RESULTS: Of the total 1,580 patients, there were 752 FC (47.6%) and 828 (52.4%) non-FC. Readmissions representing FC at months 1, 3, and 6 were 40.3%, 49.3%, and 53.4%, respectively. At index admission, the groups were demographically and clinically similar, with similar rates of abdominal operations and complications. Non-FC patients had a higher rate of abdominal reoperation at readmission (5.8% non-FC vs. 2.9% FC, p = 0.006). In an adjusted model, multiple readmissions (odds ratio [OR] 1.11, p = 0.014), readmission >30 days after index facility discharge (OR, 1.98; p < 0.001), and discharge to a nonmedical facility (OR, 2.46; p < 0.0001) were associated with increased odds of FC. Operative intervention at index admission was associated with lower odds of FC (OR, 0.77; p = 0.039). However, FC was not independently associated with demographic or insurance characteristics. CONCLUSION: The rate of FC among patients with blunt abdominal injury is high. The risk of FC is mitigated when patients are managed operatively during the index admission. Trauma systems should implement measures to ensure that these patients are followed postdischarge. LEVEL OF EVIDENCE: Prognostic and epidemiological, level III; Care management, level IV.


Assuntos
Traumatismos Abdominais/cirurgia , Assistência ao Convalescente/organização & administração , Readmissão do Paciente/estatística & dados numéricos , Centros de Traumatologia/organização & administração , Ferimentos não Penetrantes/cirurgia , Adulto , Assistência ao Convalescente/normas , Assistência ao Convalescente/estatística & dados numéricos , Idoso , Feminino , Humanos , Tempo de Internação/estatística & dados numéricos , Masculino , Pessoa de Meia-Idade , Alta do Paciente/normas , Alta do Paciente/estatística & dados numéricos , Melhoria de Qualidade/organização & administração , Melhoria de Qualidade/normas , Estudos Retrospectivos , Fatores de Risco , Fatores de Tempo , Centros de Traumatologia/normas , Centros de Traumatologia/estatística & dados numéricos , Estados Unidos
7.
J Surg Res ; 268: 491-497, 2021 12.
Artigo em Inglês | MEDLINE | ID: mdl-34438190

RESUMO

BACKGROUND: Traumatic intracranial hemorrhage (ICH) is a highly morbid injury, particularly among elderly patients on preinjury anticoagulants (AC). Many trauma centers initiate full trauma team activation (FTTA) for these high-risk patients. We sought to determine if FTTA was superior compared with those who were evaluated as a trauma consultation (CON). METHODS: Patients aged ≥55 on preinjury AC who presented from January 2015 to December 2019 with blunt isolated head injury (non-head AIS ≤2) and confirmed ICH were identified. CON patients and FTTA patients were matched by age and head AIS. Cox proportional hazard model was used to assess patient and injury characteristics with mortality and survivor discharge disposition. REASULTS: There were 45 CON patients and 45 FTTA patients. Mean age was 80 years in both groups. Fall was the most common mechanism (98% CON vs. 92% FTTA). Glasgow Coma Score (GCS) was lower in FTTA (14 vs. 15, p<0.01). CON had a significantly longer time from arrival to CT scan (1.3 vs. 0.4 hrs, p<0.01). Hospital days were similar (CON: 3.9 vs. FTTA: 3.7 days). However, CON had increased ventilator use (p=0.03). Lower admission GCS was the only factor associated with increased risk of death. Among survivors, only head AIS increased the risk of discharge to a level of care higher than that of preinjury (p=0.01). CONCLUSION: There was no difference in mortality or adverse discharge disposition between FTTA and CON, although FTTA was associated with a more rapid evaluation and diagnosis. Any alteration in GCS was strongly associated with mortality and should prompt evaluation by FTTA.


Assuntos
Hemorragia Intracraniana Traumática , Hemorragias Intracranianas , Idoso , Idoso de 80 Anos ou mais , Anticoagulantes/efeitos adversos , Escala de Coma de Glasgow , Humanos , Hemorragia Intracraniana Traumática/induzido quimicamente , Hemorragias Intracranianas/etiologia , Estudos Retrospectivos , Centros de Traumatologia
8.
Mil Med ; 186(7-8): 826-828, 2021 07 01.
Artigo em Inglês | MEDLINE | ID: mdl-33884426

RESUMO

This case report is about a 51-year-old active duty male with JAK2 mutation and medical history significant for prehepatic portal hypertension from portal vein thrombus on lifelong anticoagulation with rivaroxaban, an oral factor Xa inhibitor, presenting with closed-loop small bowel obstruction requiring emergent laparotomy. We present this surgical case as it required emergent reversal of the oral factor Xa inhibitor with andexanet alfa.


Assuntos
Inibidores do Fator Xa , Fator Xa , Coagulação Sanguínea , Inibidores do Fator Xa/farmacologia , Humanos , Masculino , Pessoa de Meia-Idade , Proteínas Recombinantes , Rivaroxabana/farmacologia
9.
Am J Surg ; 221(6): 1121-1126, 2021 06.
Artigo em Inglês | MEDLINE | ID: mdl-33745689

RESUMO

BACKGROUND: We compared surgical device malfunction reports in the Food and Drug Administration (FDA) public Manufacturer and User Facility Device Experience (MAUDE) with those in the FDA nonpublic Alternative Summary Reporting (ASR). METHODS: General surgery device product code categories in MAUDE and ASR from 1999 to 2018 were identified. Changes in the rates of categories and adverse events were evaluated by Poisson regression. RESULTS: There were 283,308 (72%) general surgical device malfunctions in MAUDE and 109,954 (28%) in ASR. Reports increased annually in ASR versus MAUDE, particularly for surgical staplers and clip devices (p < 0.05). ASR contained approximately 80% of these reports; MAUDE 20%. In MAUDE, 42.9% of surgical device malfunctions and 20.2% of stapler/clip malfunctions resulted in patient injury or death. ASR listed no injury or death information. CONCLUSIONS: ASR contained a significant portion of surgical device malfunctions hidden from public scrutiny. Access to such data is essential to safe surgical care.


Assuntos
Falha de Equipamento/estatística & dados numéricos , Instrumentos Cirúrgicos/efeitos adversos , Bases de Dados Factuais , Análise de Falha de Equipamento , Humanos , Estudos Retrospectivos , Estados Unidos , United States Food and Drug Administration
10.
Am J Surg ; 221(6): 1246-1251, 2021 06.
Artigo em Inglês | MEDLINE | ID: mdl-33707080

RESUMO

BACKGROUND: Methamphetamine (METH) is associated with an elevated risk of injury and the outcomes in the elderly remain unclear. We analyzed METH's impact in elderly trauma patients. METHODS: Retrospective analysis (2009-2018) of trauma patients at a Level I trauma center. Elderly patients were defined as age ≥55. Substance use was identified by blood alcohol test and urine drug screen. Cox proportional hazard model was used to assess patient and injury characteristics with mortality. RESULTS: Of 15,770 patient encounters with substance use testing, 5278 (34%) were elderly. Elderly METH use quadrupled over time (2%-8%; p < 0.01). Elderly METH + patients were more likely to require surgical intervention (35% vs. 17%), mechanical ventilation (15% vs. 7%), and a longer hospitalization (6.5 vs. 3.6 days) compared with elderly substance negative. Multivariate analysis showed increasing age, ventilator use, and injury severity were associated with mortality (ps < 0.01); METH was not related to mortality. CONCLUSION: Substance use in elderly trauma patients increased significantly. METH use in elderly trauma patients is a risk factor for significantly greater resource utilization.


Assuntos
Transtornos Relacionados ao Uso de Anfetaminas/complicações , Metanfetamina/efeitos adversos , Ferimentos e Lesões/etiologia , Fatores Etários , Idoso , Consumo de Bebidas Alcoólicas/efeitos adversos , Consumo de Bebidas Alcoólicas/epidemiologia , Transtornos Relacionados ao Uso de Anfetaminas/epidemiologia , California/epidemiologia , Feminino , Humanos , Escala de Gravidade do Ferimento , Tempo de Internação , Masculino , Metanfetamina/uso terapêutico , Pessoa de Meia-Idade , Modelos de Riscos Proporcionais , Sistema de Registros , Estudos Retrospectivos , Fatores de Risco , Detecção do Abuso de Substâncias , Centros de Traumatologia/estatística & dados numéricos , Ferimentos e Lesões/epidemiologia
11.
J Trauma Acute Care Surg ; 91(1): 40-46, 2021 07 01.
Artigo em Inglês | MEDLINE | ID: mdl-33605703

RESUMO

BACKGROUND: Partial resuscitative endovascular balloon occlusion of the aorta (pREBOA) is a technology that occludes aortic flow and allows for controlled deflation and restoration of varying distal perfusion. Carotid flow rates (CFRs) during partial deflation are unknown. Our aim was to measure CFR with the different pREBOA balloon volumes and correlate those to the proximal mean arterial pressure (PMAP) and a handheld pressure monitoring device (COMPASS; Mirador Biomedical, Seattle, WA). METHODS: Ten swine underwent a hemorrhagic injury model with carotid and iliac arterial pressures monitored via arterial lines. Carotid and aortic flow rates were monitored with Doppler flow probes. A COMPASS was placed to monitor proximal pressure. The pREBOA was inflated for 15 minutes then partially deflated for an aortic flow rate of 0.7 L/min for 45 minutes. It was then completely deflated. Proximal mean arterial pressures and CFR were measured, and correlation was evaluated. Correlation between CRF and COMPASS measurements was evaluated. RESULTS: Carotid flow rate increased 240% with full inflation. Carotid flow rate was maintained at 100% to 150% of baseline across a wide range of partial deflation. After full deflation, CFR transiently decreased to 45% to 95% of baseline. There was strong positive correlation (r > 0.85) between CFR and PMAP after full inflation, and positive correlation with partial inflation (r > 0.7). Carotid flow rate had strong correlation with the COMPASS with full REBOA (r > 0.85) and positive correlation with pREBOA (r > 0.65). CONCLUSION: Carotid flow rate is increased in a hemorrhagic model during full and partial inflation of the pREBOA and correlates well with PMAP. Carotid perfusion appears maintained across a wide range of pREBOA deflation and could be readily monitored with a handheld portable COMPASS device instead of a standard arterial line setup.


Assuntos
Oclusão com Balão/efeitos adversos , Circulação Cerebrovascular , Técnicas Hemostáticas/efeitos adversos , Ressuscitação/efeitos adversos , Choque Hemorrágico/terapia , Animais , Aorta/cirurgia , Oclusão com Balão/instrumentação , Velocidade do Fluxo Sanguíneo , Artérias Carótidas/fisiologia , Modelos Animais de Doenças , Técnicas Hemostáticas/instrumentação , Humanos , Masculino , Ressuscitação/instrumentação , Ressuscitação/métodos , Suínos
12.
J Trauma Acute Care Surg ; 90(4): 615-622, 2021 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-33405469

RESUMO

BACKGROUND: Partial resuscitative endovascular balloon occlusion of the aorta (pREBOA) attempts to minimize ischemia/reperfusion injury while controlling hemorrhage. There are little data on optimal methods to evaluate and titrate partial flow, which typically requires invasive arterial line monitoring. We sought to examine the use of a miniaturized handheld digital pressure device (COMPASS; Mirador Biomedical, Seattle, WA) for pREBOA placement and titration of flow. METHODS: Ten swine underwent standardized hemorrhagic shock. Carotid and iliac pressures were monitored with both arterial line and COMPASS devices, and flow was monitored by aortic and superior mesenteric artery flow probes. Partial resuscitative endovascular balloon occlusion of the aorta was inflated to control hemorrhage for 15 minutes before being deflated to try targeting aortic flow of 0.7 L/min (using only the COMPASS device) by an operator blinded to the arterial line pressures and aortic flow. Correlations between COMPASS and proximal/distal arterial line were evaluated, as well as actual aortic flow. RESULTS: There was strong correlation between the distal mean arterial pressure (MAP) and the distal COMPASS MAP (r = 0.979, p < 0.01), as well as between the proximal arterial line and the proximal COMPASS on the pREBOA (r = 0.989, p < 0.01). There was a significant but weaker correlation between the distal compass MAP reading and aortic flow (r = 0.47, p < 0.0001), although it was not clinically significant and predicted flow was not achieved in a majority of the procedures. Of 10 pigs, survival times ranged from 10 to 120 minutes, with a mean survival of 50 minutes, and 1 pig surviving to 120 minutes. CONCLUSION: Highly reliable pressure monitoring is achieved proximally and distally without arterial lines using the COMPASS device on the pREBOA. Despite accurate readings, distal MAPs were a poor indicator of aortic flow, and titration based upon distal MAPs did not provide reliable results. Further investigation will be required to find a suitable proxy for targeting specific aortic flow levels using pREBOA.


Assuntos
Oclusão com Balão , Monitores de Pressão Arterial , Procedimentos Endovasculares , Sistemas Automatizados de Assistência Junto ao Leito , Choque Hemorrágico/fisiopatologia , Choque Hemorrágico/terapia , Animais , Aorta/fisiopatologia , Pressão Arterial , Modelos Animais de Doenças , Masculino , Traumatismo por Reperfusão/prevenção & controle , Reprodutibilidade dos Testes , Ressuscitação , Suínos
13.
Artigo em Inglês | MEDLINE | ID: mdl-22683555

RESUMO

Carrier-type molecular ionophores, such as the cyclic dodecadepsipeptide valinomycin, often must undergo structural changes during the binding and transport of a cation across the lipid membrane. Observing the structural fluctuations that occur during this process experimentally has proven extremely difficult due to the complexities of spectroscopic analysis of protein structure/dynamics in native lipid bilayer environments. Currently, our understanding of how valinomycin selectively transports ions across membranes is derived from atomic structures solved of the cyclic macromolecule solvated in various organic solvents and complimentary in silico dynamics experiments. We have shown recently that deep-UV excited resonance Raman spectroscopy (DUVRR) has a unique ability to characterize secondary structure content and simultaneously provide information about the relative solvation of the probed peptide backbone C.M. Halsey, J. Xiong, O. Oshokoya, J.A. Johnson, S. Shinde, J.T. Beatty, G. Ghirlanda, R.D. JiJi, J.W. Cooley, Simultaneous observation of peptide backbone lipid solvation and a-helical structure by deep-UV resonance Raman spectroscopy, ChemBioChem 12 (2011) 2125-2128, [16]. Interpretation of DUVRR spectra of valinomycin in swelled lipid and unilamellar lipid bilayer environments indicate that the uncomplexed valinomycin molecule dynamically samples both the open and closed conformations as described for the structures derived from polar and non-polar organic solvents, respectively. Upon introduction of potassium, the structure of valinomycin in swelled lipid environments resembles more closely that of the open conformation. The shift in structure upon complexation is accompanied by a significant decrease in the valinomycin DUVRR spectral amide I intensity, indicating that the open conformation is more water solubilized and is seemingly "trapped" or predominantly located close to the lipid-water interface. The trapping of the valinomycin in the act of complex of potassium at the bilayer-solvent interface and its analysis by DUVRR represents the first spectroscopic description of this state. Conversely, an opposite trend is observed in the amide I intensity upon potassium complexation in unilamellar (or extruded) vesicles, implying the predominant conformation upon potassium binding in native bilayers is one where the peptide backbone of valinomycin is desolvated as would be expected if the molecule were more readily able to traverse a bilayer interior. Interpretation of the DUVRR spectral features is also consistent with the loss or formation of hydrogen bonds observed in the open and closed structures, respectively. Valinomycin must then sample several conformations in the absence of appropriate ions depending upon its locale in the lipid bilayer until potassium causes a greater degree of closure of the open conformer and an increased residency within the more non-polar interior. The potassium induced decreased solubility enables diffusion across the membrane where potassium release can occur by equilibration at the opposite lipid water interface.


Assuntos
Lipídeos/química , Potássio/química , Valinomicina/química , Cátions , Modelos Moleculares , Conformação Molecular , Cloreto de Potássio/química , Cloreto de Sódio/química , Solubilidade , Análise Espectral Raman , Raios Ultravioleta
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