Role of cyclooxygenases 1 and 2 in the maintenance of colonic mucosal integrity in an experimental colitis model

The role of cyclooxygenase (COXs) isoforms in maintaining colonic mucosal integrity is not fully understood. This study aimed to evaluate the role of COX-1 and -2 on colonic mucosal integrity in an experimental colitis model. Colitis was induced in Wistar rats by intracolonic administration of 2,4,6-trinitrobenzenesulfonic acid (20 mg + 50% ethanol). The control group (sham group) received saline only. After 7, 14, or 28 days, colonic samples were removed, and macroscopic lesion scores, wet weight, myeloperoxidase activity, and transepithelial electrical resistance (TER) were determined. In other rat groups, colonic samples from the sham group and a 7th day post-colitis group were mounted in Üssing chambers with the luminal side exposed to a buffer solution (control), acetylsalicylic acid (ASA), SC-560 (COX-1 inhibitor), or celecoxib (COX-2 inhibitor). TER and epithelial permeability to fluorescein were measured. The 7th day colitis group had higher macroscopic damage scores, wet weight, and myeloperoxidase activity and lower basal TER than the sham, 14th day colitis, and 28th day colitis groups. Inhibition of COX-1 but not COX-2 significantly decreased TER and increased permeability to fluorescein in the 7th day post-colitis group compared to the sham group. Additionally, ASA decreased the colonic mucosal integrity on day seven post-colitis compared to the sham group. A decrease in the colonic mucosa integrity in the experimental colitis model can be aggravated only by the inhibition of COX-1, which demonstrated the importance of this enzyme in the maintenance of colonic mucosal integrity.

Short-term outcomes in patients with non-ST-segment elevation myocardial infarction

Funding Acknowledgements

Type of funding sources: None.

Introduction

The proportion of non-ST-segment elevation myocardial infarction (NSTEMI) is increasing among the acute coronary syndromes (ACS). Reinfarction (RI) is a potential complication in high-risk patients with NSTEMI and it will cause an impact on these patients’ prognosis.

Purpose

Identify high-risk patients with RI and their prognosis in the setting of NSTEMI.

Methods

Based on a multicenter retrospective study, data collected from admissions between January 2013 and January 2020. Patients without data on previous cardiovascular history or uncompleted clinical data were excluded. Patients were divided in 2 groups (G): G1 – patients without RI; G2 - patients with RI during hospitalization. Logistic regression and survival analysis were performed.

Results

7180 patients were admitted with NSTEMI, RI occurred in 71 pts (0.99%). Regarding epidemiological and past history G2 was older (71±12 vs 66±12, p=0.001), had higher rates of previous stroke (15.9% vs 7.0%, p 0.003) and peripheric arterial disease (6.3% vs 6.1%, p=0.004). The groups were similar regarding arterial hypertension (p=0.74), diabetes type 2 (p=0.11) and dyslipidaemia (p=0.48).

G2 had higher levels of brain natriuretic peptide (45.5% vs 24.5%, p<0.001) and lower levels of haemoglobin (20.3% vs 7.9%, p<0.001). Patients taking prasugrel (2% vs 0.3%, p=0.002) or ticagrelor (6.1% vs 2.2%, p<0.001) previously to the admission were more susceptible to have RI. Patients with severe left ventricular systolic dysfunction (3.4% vs 2.6%, p<0.001), need of invasive (2.8% vs 0.8%, p<0.001) or non-invasive (4.2% vs 1.3%, p<0.001) ventilation and percutaneous coronary intervention (PCI) (80.3% vs 64.7%, p0.006) had higher rates of RI.

Logist regression confirmed that PCI (p=0.03, OR 2.22, CI 1.08-4.53), previous stroke (p=0.02, OR 0.58, CI 0.37-0.92) and pts previously taking prasugrel (p=0.02, OR 1.85, CI 1.11-3.10) were predictors of RI in the setting of NSTEMI.

Conclusion

RI in the setting of NSTEMI was associated with PCI, previous stroke and pts previously taking prasugrel. One year prognosis was poorer for patients who suffered RI.

Can we prevent the occurrence of stroke in patients admitted with non-ST-segment elevation myocardial infarction?

Funding Acknowledgements

Type of funding sources: None.

Introduction

Cardio-cerebral vascular diseases are a leading cause of deaths worldwide.

Stroke is a potential complication in high-risk patients who had non-ST-segment elevation myocardial infarction (NSTEMI).

Purpose

Identify high-risk patients with stroke and their prognosis in the setting of NSTEMI.

Methods

Based on a multicenter retrospective study, data collected from admissions between January 2013 and January 2020. Patients without data on previous cardiovascular history or uncompleted clinical data were excluded. Patients were divided in 2 groups (G): G1 – patients who suffered stroke; G2 - patients without stroke. Logistic regression and survival analysis were performed.

Results

7180 patients were admitted with NSTEMI, stroke occurred in 35 patients (0.49%). Regarding epidemiological and past history G1 was older (72±9 vs 66±12, p= 0.004), had more females (54.3% vs 45.75, p<0.001), had higher rates of type 2 diabetes mellitus (51.3% vs 35.2%, p=0.05), previous strokes / transient ischemic attack (24.2% vs 7.0%, p=0.007) and dementia (3.3% vs 0.8%, p<0.001). Arterial hypertension (77.1 vs 72.8%, p=0.56), dyslipidaemia (61.8% vs 63.0%, p=0.88) and smoking (17.6% vs 26.0%, p=0.27) were similar between groups. Patients who presented with chest pain (72.7% vs 92.0%, p<0.001) and patients who were not revascularized were more likely to suffer a stroke (43.3% vs 17.5%, p<0.001).

Logist regression only confirmed that females were more likely to have a stroke (p<0.001, OR 4.13, CI 1.87-9.15) and patients who presented with chest pain (p=0.001, OR 0.23, CI 0.10-0.54). One year event-free survival was higher in patients who did not have stroke (95.3% vs 80.0%, p=0.005, OR 4.50, CI 1.43-14.15)

Conclusion

Since sex gender and form of presentation of NSTEMI are not modifiable factors we cannot prevent strokes from happening in the context of NSTEMI.

Endocardial left ventricular pacing Where are we a systematic review

Funding Acknowledgements

Type of funding sources: None.

Background

Endocardial left ventricular pacing is a technique used in cardiac resynchronization therapy (CRT), when a coronary sinus implant is not possible, conventional CRT was an unsuccess and in CRT nonresponders. We performed a systemic review to evaluate its risks and benefits.

Objective

Review the evidence regarding the efficacy and safety of endocardial left ventricular pacing.

Methods

A systemic research on MEDLINE and PUBMED with the term "endocardial left ventricular pacing", "biventricular pacing" or "endocardial left pacing". 1038 results were identified, however, just publish papers (excluding abstract) with more than 16 patients was admitted in these analyses. Comparisons pre and post CRT regard New York Heart Association (NYHA) functional classification, left ventricular ejection fraction (LVEF) and QRS width was performed. Mean differences (MD) and confidence interval (CI) was used as a measurement of treatment.

Results

Eleven studies were selected, including a total of 560 patients. The studies were performed with different techniques, trans-atrial septal technique, trans-ventricular septal technique and transapical technique. Mean age 66.93 years old, 90.54% male, median ejection fraction of 28.86%, NYHA class of 3.03, QRS width 167,50 mseg. Ischemic etiologic in 43.88%, atrial fibrillation in 45.35% and left bundle branch block in 55.20%. Was reported several complications after the procedure, 8 pocket infection (7 studies), 17 transient ischemic attacks (10 papers), 17 ischemic stroke (all), 35 tromboembolic events (all) and 115 deaths, nevertheless, follow up in the different studies was diverse and heterogeneous. Significant improvement was registered in NYHA class (MD 0.64, CI 0.56-0.72, p < 0.00001, I2 = 89%) (reported in 7 studies), LVEF (MD 6.20, CI 5.09-7.32, p = 0.002, I2 = 69%) %) (reported in 8 studies) and QRS width (MD 31.35, CI 26.11-36.60, p < 0.00001, I2 = 89%) %) (reported in 5 studies), (all p < 0.00001).

Conclusions

Left ventricular endocardial pacing is a feasible alternative to conventional CRT, when the last one is not possible. With clinical, electrocardiogram and echocardiogram improvement in several series. First data regarding this procedure were associated with higher stroke incidence, something contrary to the last study’s results. Nevertheless, at the moment just small series present this technique with heterogenous results and different approaches, being important further investigation.

Septal vs apical defibrillator electrode placement a systematic review

Funding Acknowledgements

Type of funding sources: None.

Background

The optimal right ventricular defibrillator lead placement is still a debatable matter. We attempt to performed a systemic review to evaluate whether septal and apical placement had significant differences in the follow-up with an indication for implantation of these devices.

Objective

Review the evidence regarding the efficacy and safety of right ventricular apical and septal defibrillator lead placement.

Methods

A systemic research on MEDLINE and PUBMED with the term "septal pacing", "apical pacing" "septal defibrillation" or "apical defibrillation". 309 results were identified, however, after a serious analysis, several articles were excluded. Comparisons between apical and septal placement were performed regarding R wave amplitude, pacing threshold at 0.5 ms, lead impedance, left ventricular ejection fraction (LVEF), left ventricular end-diastolic diameter (LVEDD) and lead complication that produced lead re-placement. Mean differences (MD) and confidence interval (CI) was used as a measurement of treatment.

Results

Six studies were selected, including a total of 2180 patients. The studies were performed with different techniques, analyses and goals. The studies presented heterogeneous and diverse results, with a varied follow-up period, that resulted in the exclusion of one of the studies. Mean age 64.51 years old, 76.86% male, a median ejection fraction of 27.84%, NYHA class of 2.65, ischemic etiologic in 51.10% and a follow-up period of 26.49 months. Septal defibrillator lead placement was established in 772 patients, while the apical defibrillator lead placement was performed in 1399 patients. No differences regarding the lead performance on apical and septal placement were detected regarding the R-wave (MD -0.36, CI -0.75 - +0.03, p = 0.68, I2 = 0%) (reported in 3 studies) and lead impedance (MD -23.83, CI -51.36 - +3.69, p = 0.003, I2 = 82%) (reported in 3 studies). Pacing threshold seems to be favor a septal defibrillator lead implantation (MD -0.05, CI -0.09 - -0.02, p = 0.12, I2 = 53%) (reported in 3 studies). Concerning echocardiography parameters during the follow up period, LVEF (MD -0.83, CI -3.05 - +1.38, p = 0.10, I2 = 57%) (reported in 3 studies) and LVEDD (MD -0.51, CI -2.13 - +1.10, p = 0.20, I2 = 38%) (reported in 3 studies) were not significant influenced for the defibrillator lead placement. Lead complications that provoke a lead replacement was not significant between the lead placement (MD 1.25, CI 0.53 – 2.94, p = 0.71, I2 = 0%) (reported in 3 studies).

Conclusions

Just pacing threshold proved to improve the septal defibrillator lead placement. Neither the other lead parameters or the echocardiography results during the follow-up were influenced by the lead placement. For a definitive conclusion is important to further investigation.

Acute heart failure: does etiology matter?

Funding Acknowledgements

Type of funding sources: None.

Introduction

Patients (pts) with acute heart failure (AHF) are a heterogeneous population. The etiology of the heart disfunction may play a role in prognosis. Risk stratification at admission may help predict in-hospital complications and needs.

Objective

To explore predictors of in-hospital mortality (IHM), post discharge early mortality [1-month mortality (1mM)] and late mortality [1-year mortality (1yM)] and early and late readmission, respectively 1-month readmission (1mRA) and 1-year readmission (1yRA), in our center population, using real-life data.

Methods

Based on a single-center retrospective study, data collected from patients (pts) admitted in the Cardiology department with AHF between 2010 and 2017. Pts without data on previous cardiovascular history or uncompleted clinical data were excluded. The pts were divided in 3 groups: ischemic etiology (IE), valvular etiology (VE) and other etiologies (OE), which included hypertensive and idiopathic cardiomyopathies). Statistical analysis used non-parametric tests and Kaplan-Meyer survival analysis.

Results

We included 300 pts admitted with AHF. Mean age was 67.4 ± 12.6 years old and 72.7% were male. 37.7% had previous history of revascularization procedures, 66.9% had hypertension, 41% were diabetic and 38% had dyslipidaemia. The heart failure was of IE in 45%, VE in 22.7% and of OE in 32.3% of the cases.

There were no significant differences between groups regarding body mass index, Killip-Kimball class, systolic blood pressure at admission, blood tests aspects at admission (namely, creatinine, sodium or urea), inotropes’ usage or need of non-invasive or invasive ventilation. However, IE group had higher percentage of males comparing to VE e OE (83.0% vs 55.9% vs 70.1%, respectively, p < 0.001), higher rates of prior revascularization procedures (68.9%, vs 19.1%, vs 7.2%, p < 0.001) and higher rates of traditional cardiovascular risk factors, namely hypertension (74.1% vs 55.9% vs 57.7%, p = 0.014), diabetes mellitus (48.1% vs 27.9% vs 27.8%, p = 0.002) and dyslipidaemia (48.9% vs 30.9% vs 40.2%, p = 0.022). OE group was younger compared to IE and VE (63.9 ± 13.5 vs 68.9 ± 11.1 vs 69.5 ± 13.0 years old, respectively, p = 0.003). VE group had less left ventricle disfunction comparing to IE and VE groups (left ventricle ejection fraction 40.8 ± 14.1 vs 32.2 ± 9.8 vs 31.6 ± 12.8%, respectively, p < 0.001).

The groups showed no significant differences regarding IHM (IE 5.2% vs VE 8.8% vs OE 2.1%, p = 0.146), 1mRA (IE 8.1&, VE 7.4%, OE 3.1%, p = 0.276) or 1yRA (IE 55.6%, VE 54.4%, OE 47.4%, p = 0.449). However, VE group had higher rates of 1mM (VE 13.2% vs IE 8.9% vs OE 3.1%, p = 0.05) and 1yM compared to IE and OE (33.8% vs 30.4% vs 17.5%, respectively, p = 0.34). These aspects are represented in Kaplan Meier survival curves.

Conclusion

In our population, the etiology of heart failure was predictor of early and late post-discharge mortality but not readmission.

Acute heart failure: is ACTION-ICU useful?

Funding Acknowledgements

Type of funding sources: None.

Introduction

Patients (pts) with acute heart failure (AHF) are a heterogeneous population. Risk stratification at admission may help predict in-hospital complications and needs. ACTION ICU score is validated to estimate the risk of complications requiring ICU care in non-ST elevation acute coronary syndromes.

Objective

To validate ACTION-ICU score in AHF as predictor of in-hospital M (IHM), post discharge early M [1-month mortality (1mM)] and 1-month readmission (1mRA), in our center population, using real-life data.

Methods

Based on a single-center retrospective study, data collected from pts admitted in the Cardiology department with AHF between 2010 and 2017. Pts without data on previous cardiovascular history or uncompleted clinical data were excluded. Statistical analysis used non-parametric tests, logistic regression analysis and ROC curve analysis.

Results

We included 300 pts admitted with AHF. Mean age was 67.4 ± 12.6 years old and 72.7% were male. 37.7% had previous history of revascularization procedures, 66.9% had hypertension, 41% were diabetic and 38% had dyslipidaemia. Mean heart rate was 95.5 ± 27.5bpm, mean systolic blood pressure (SBP) was 131.2 ± 37.0mmHg, mean urea level at admission was 68.8 ± 40.7mg/dL, mean sodium was 137.6 ± 4.7mmol/L, mean glomerular filtration rate (GFR) was 57.1 ± 23.5ml/min. 35.3% were admitted in Killip-Kimball class (KKC) 4. Mean ACTION-ICU score was 10.4 ± 2.3. Inotropes’ usage was necessary in 32.7% of the pts, 11.3% of the pts needed non-invasive ventilation (NIV), 8% needed invasive ventilation (IV). IHM rate was 5% and 1mM was 8%. 6.3% of the pts were readmitted 1 month after discharge.

Older age (p < 0.001), lower SBP (p = 0,035), presenting in KKC 4 (p < 0.001, OR 8.13) and need of inotropes (p < 0.001) were predictors of IHM in our population. Older age (OR 1.06, p = 0.002, CI 1.02-1.10), lower SBP (OR 1.01, p = 0.05, CI 1.00-1.02) and lower left ventricle ejection fraction (LVEF) (OR 1.06, p < 0.001, CI 1.03-1.09) were predictors of need of NIV. None of the studied variables were predictive of need of IV. LVEF (OR 0.924, p < 0.001, CI 0.899-0.949), lower SBP (OR 0.80, p < 0.001, CI 0.971-0.988), higher urea (OR 1.01, p < 0.001, CI 1.005-1.018) and lower sodium (OR 0.92, p = 0.002, CI 0.873-0.971) were predictors inotropes’ usage.

ACTION-ICU was able to predict IHM (OR 1.51, p = 0.02, CI 1.158-1.977), 1mM (OR 1.45, p = 0.002, CI 1.15-1.81) and inotropes’ usage (OR 1.22, p = 0.002, CI 1.08-1.39), but not 1mRA, the need of IV or NIV.

ROC curve analysis revealed ACTION-ICU performs well when predicting IHM (Area under curve (AUC) 0.729, confidence interval (CI) 0.59-0.87), inotropes’ usage (AUC 0.619, CI 0.54-0.70) and 1mM (AUC 0.705, CI 0.58-0.84).

Conclusion

In our population, ACTION-ICU score was able to predict IHM, 1mM and inotropes’s usage.

Acute heart failure: predicting early in-hospital outcomes

Funding Acknowledgements

Type of funding sources: None.

Introduction

Patients (P) with acute heart failure (AHF) are a heterogeneous population. Risk stratification at admission may help predict in-hospital complications and needs. The Get With The Guidelines Heart Failure score (GWTG-HF) predicts in-hospital mortality (M) of P admitted with AHF. ACTION ICU score is validated to estimate the risk of complications requiring ICU care in non-ST elevation acute coronary syndromes.

Objective

To validate ACTION-ICU score in AHF and to compare ACTION-ICU to GWTG-HF as predictors of in-hospital M (IHM), early M [1-month mortality (1mM)] and 1-month readmission (1mRA), using real-life data.

Methods

Based on a single-center retrospective study, data collected from P admitted in the Cardiology department with AHF between 2010 and 2017. P without data on previous cardiovascular history or uncompleted clinical data were excluded. Statistical analysis used chi-square, non-parametric tests, logistic regression analysis and ROC curve analysis.

Results

Among the 300 P admitted with AHF included, mean age was 67.4 ± 12.6 years old and 72.7% were male. Systolic blood pressure (SBP) was 131.2 ± 37.0mmHg, glomerular filtration rate (GFR) was 57.1 ± 23.5ml/min. 35.3% were admitted in Killip-Kimball class (KKC) 4. ACTION-ICU score was 10.4 ± 2.3 and GWTG-HF was 41.7 ± 9.6. Inotropes’ usage was necessary in 32.7% of the P, 11.3% of the P needed non-invasive ventilation (NIV), 8% needed invasive ventilation (IV). IHM rate was 5% and 1mM was 8%. 6.3% of the P were readmitted 1 month after discharge.

Older age (p < 0.001), lower SBP (p = 0,035) and need of inotropes (p < 0.001) were predictors of IHM in our population. As expected, patients presenting in KKC 4 had higher IHM (OR 8.13, p < 0.001). Older age (OR 1.06, p = 0.002, CI 1.02-1.10), lower SBP (OR 1.01, p = 0.05, CI 1.00-1.02) and lower left ventricle ejection fraction (LVEF) (OR 1.06, p < 0.001, CI 1.03-1.09) were predictors of need of NIV. None of the variables were predictive of IV. LVEF (OR 0.924, p < 0.001, CI 0.899-0.949), lower SBP (OR 0.80, p < 0.001, CI 0.971-0.988), higher urea (OR 1.01, p < 0.001, CI 1.005-1.018) and lower sodium (OR 0.92, p = 0.002, CI 0.873-0.971) were predictors of inotropes’ usage.

Logistic regression showed that GWTG-HF predicted IHM (OR 1.12, p < 0.001, CI 1.05-1.19), 1mM (OR 1.10, p = 1.10, CI 1.04-1.16) and inotropes’s usage (OR 1.06, p < 0.001, CI 1.03-1.10), however it was not predictive of 1mRA, need of IV or NIV. Similarly, ACTION-ICU predicted IHM (OR 1.51, p = 0.02, CI 1.158-1.977), 1mM (OR 1.45, p = 0.002, CI 1.15-1.81) and inotropes’ usage (OR 1.22, p = 0.002, CI 1.08-1.39), but not 1mRA, the need of IV or NIV. ROC curve analysis revealed that GWTG-HF score performed better than ACTION-ICU regarding IHM (AUC 0.774, CI 0.46-0-90 vs AUC 0.731, CI 0.59-0.88) and 1mM (AUC 0.727, CI 0.60-0.85 vs AUC 0.707, CI 0.58-0.84).

Conclusion

In our population, both scores were able to predict IHM, 1mM and inotropes’s usage.

Polarity of the ATP binding site of the Na+,K+-ATPase, gastric H+,K+-ATPase and sarcoplasmic reticulum Ca2+-ATPase

A fluorescence ratiometric method utilizing the probe eosin Y is presented for estimating the ATP binding site polarity of P-type ATPases in different conformational states. The method has been calibrated by measurements in a series of alcohols and tested using complexation of eosin Y with methyl-β-cyclodextrin. The results obtained with the Na⁺,K⁺-, H⁺,K⁺- and sarcoplasmic reticulum Ca²⁺-ATPases indicate that the ATP binding site, to which eosin is known to bind, is significantly more polar in the case of the Na⁺,K⁺- and H⁺,K⁺-ATPases compared to the Ca²⁺-ATPase. This result was found to be consistent with docking calculations of eosin with the E2 conformational state of the Na⁺,K⁺-ATPase and the Ca²⁺-ATPase. Fluorescence experiments showed that eosin binds significantly more strongly to the E1 conformation of the Na⁺,K⁺-ATPase than the E2 conformation, but in the case of the Ca²⁺-ATPase both fluorescence experiments and docking calculations showed no significant difference in binding affinity between the two conformations. This result could be due to the fact that, in contrast to the Na⁺,K⁺- and H⁺,K⁺-ATPases, the E2-E1 transition of the Ca²⁺-ATPase does not involve the movement of a lysine-rich N-terminal tail which may affect the overall enzyme conformation. Consistent with this hypothesis, the eosin affinity of the E1 conformation of the Na⁺,K⁺-ATPase was significantly reduced after N-terminal truncation. It is suggested that changes in conformational entropy of the N-terminal tail of the Na⁺, K⁺- and the H⁺,K⁺-ATPases during the E2-E1 transition could affect the thermodynamic stability of the E1 conformation and hence its ATP binding affinity.

Fuel loading and flammability in the Mediterranean Basin woody species with different post-fire regenerative strategies

The flammability and combustibility of plant communities are determined by species features related to growth-form, structure and physiology. In some ecosystems, such as the Mediterranean ones, these characteristics may contribute to the existence of fire-prone species. We measured several parameters associated with the flammability and fuel loading of dominant woody species with different post-fire regenerative strategies (seeders and non-seeders) in shrublands in the western Mediterranean Basin. Overall, seeder species show lower fuel load but are more prone to burning owing to a higher dead-to-live fuel ratio, live fine-fuel proportion and dead fine-fuel proportion. Moreover, they burst into flame at lower temperatures than non-seeders. In the Mediterranean Basin, most seeder species emerged mainly during the Quaternary, under a highly fluctuating Mediterranean climate and during recurrent fires. We propose that properties related to the combustibility and flammability of seeders may be the result of selective pressures associated with both fire and climate. These results suggest that ecosystems dominated by seeder species are more susceptible to fire risk than those dominated by non-seeder species in the Mediterranean Basin. Therefore, the proportion of these types of species resulting from previous fire or management history is likely to determine the characteristics of future fire events.

Proton translocation by bacteriorhodopsin in the absence of substantial conformational changes

Unlike wild-type bacteriorhodopsin (BR), the BR triple mutant D96G/F171C/F219L has been shown to undergo only minor structural rearrangements during its photocycle. Nonetheless, the mutant is capable of transporting protons at a rate of 125(+/-40) H+/BR per minute under light-saturating conditions. Light adaptation of the triple mutant's retinal proceeds in a pH-dependent manner up to a maximum of 63% all-trans. These two findings imply that the transport activity of the triple mutant comprises 66% of the wild-type activity. Time-resolved spectroscopy reveals that the identity and sequence of intermediates in the photocycle of the triple mutant in the all-trans configuration correspond to that of wild-type BR. The only differences relate to a slower rise and decay of the M and O intermediates, and a significant spectral contribution from a 13-cis component. No indication for accumulation of the N intermediate is found under a variety of conditions that normally favor the formation of this species in wild-type BR. The Fourier transform infrared (FTIR) spectrum of the M intermediate in the triple mutant resembles that of wild type. Minor changes in the amide I region during the photocycle suggest that only small movements of the protein backbone occur. Electron microscopy reveals large differences in conformation between the unilluminated state of the mutant protein and wild-type but no light-induced changes in time-resolved measurements. Evidently, proton transport by the triple mutant does not require the major conformational rearrangements that occur on the same time-scale with wild-type. Thus, we conclude that large conformational changes observed in the photocycle of the wild-type and many BR mutants are not a prerequisite for the change in accessibility of the Schiff base nitrogen atom that must occur during vectorial catalysis to allow proton transport.

Roles of cytoplasmic arginine and threonine in chloride transport by the bacteriorhodopsin mutant D85T

In the light-driven anion pump halorhodopsin (HR), the residues arginine 200 and threonine 203 are involved in anion release at the cytoplasmic side of the membrane. Because of large sequence homology and great structural similarities between HR and bacteriorhodopsin (BR), it has been suggested that anion translocation by HR and by the chloride-pumping BR mutant BR-D85T occurs by the same mechanism. Consequently, the functions of the R200/T203 pair in HR should be the same as those of the corresponding pair in BR-D85T (R175/T178). We have put this hypothesis to a test by creating two mutants of BR-D85T in which R175 and T178 were replaced by glutamine and valine, respectively. Chloride transport activities were essentially the same for all three mutants, whereas chloride binding and the kinetics of parts of the photocycle were markedly affected by the replacement of T178. In contrast, the consequences of mutating R175 proved to be less significant. These findings are consistent with evidence obtained on HR and therefore support the idea that the respective mechanistic roles of the cytoplasmic arginine/threonine pairs in HR and BR-D85T are equal.

Water transport by the bacterial channel alpha-hemolysin

This study is an investigation of the ability of the bacterial channel alpha-hemolysin to facilitate water permeation across biological membranes. alpha-Hemolysin channels were incorporated into rabbit erythrocyte ghosts at varying concentrations, and water permeation was induced by mixing the ghosts with hypertonic sucrose solutions. The resulting volume decrease of the ghosts was followed by time-resolved optical absorption at pH 5, 6, and 7. The average single-channel permeability coefficient of alpha-hemolysin for water ranged between 1.3x10-12 cm/s and 1.5x10-12 cm/s, depending on pH. The slightly increased single-channel permeability coefficient at lower pH-values was attributed to an increase in the effective pore size. The activation energy of water transport through the channel was low (Ea=5.4 kcal/mol), suggesting that the properties of water inside the alpha-hemolysin channel resemble those of bulk water. This conclusion was supported by calculations based on macroscopic hydrodynamic laws of laminar water flow. Using the known three-dimensional structure of the channel, the calculations accurately predicted the rate of water flow through the channel. The latter finding also indicated that water permeation data can provide a good estimate of the pore size for large channels.

Proton and electron transfer during the reduction of molecular oxygen by fully reduced cytochrome c oxidase: a flow-flash investigation using optical multichannel detection

Proton and electron transfer events during the reaction of solubilized fully reduced bovine heart cytochrome c oxidase with molecular oxygen were investigated using the flow-flash technique. Time-resolved spectral changes resulting from ligand binding and electron transfer events were detected simultaneously with pH changes in the bulk. The kinetics and spectral changes in the visible region (450-750 nm) were probed by optical multichannel detection, allowing high spectral resolution on time scales from 50 ns to 50 ms. Experiments were carried out in the presence and absence of pH-sensitive dyes (carboxyfluorescein at pH 6.5, phenol red at pH 7.5, and m-cresol purple at pH 8.5) which permitted separation of spectral changes due to proton transfer from those caused by ligand binding and electron transfer. The transient spectra recorded in the absence of dye were analyzed by singular-value decomposition and multiexponential fitting. Five apparent lifetimes (0.93 microseconds, 10 microseconds, 36 microseconds, 90 microseconds, and 1.3 ms at pH 7.5) could consistently be distinguished and provided a basis for a reaction mechanism consistent with our most recent kinetic model [Sucheta, A., Szundi, I., and Einarsdóttir, O. (1999) Biochemistry 37, 17905-17914]. The dye response indicated that proton uptake occurred concurrently with the two slowest electron transfer steps, in agreement with previous results based on single-wavelength detection [Hallén, S., and Nilsson, T. (1992) Biochemistry 31, 11853-11859]. The stoichiometry of the proton uptake reactions was approximately 1.3 +/- 0.3, 1.4 +/- 0.3, and 1.6 +/- 0.5 protons per enzyme at pH 6.5, 7.5, and 8.5, respectively. The electron transfer between heme a and CuA was limited by proton uptake on a 90 microseconds time scale. We have established the lower limit of the true rate constant for the electron transfer between CuA and heme a to be approximately 2 x 10(5) s-1.

Permeation of halide anions through phospholipid bilayers occurs by the solubility-diffusion mechanism

Two alternative mechanisms are frequently used to describe ionic permeation of lipid bilayers. In the first, ions partition into the hydrophobic phase and then diffuse across (the solubility-diffusion mechanism). The second mechanism assumes that ions traverse the bilayer through transient hydrophilic defects caused by thermal fluctuations (the pore mechanism). The theoretical predictions made by both models were tested for halide anions by measuring the permeability coefficients for chloride, bromide, and iodide as a function of bilayer thickness, ionic radius, and sign of charge. To vary the bilayer thickness systematically, liposomes were prepared from monounsaturated phosphatidylcholines (PC) with chain lengths between 16 and 24 carbon atoms. The fluorescent dye MQAE (N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide) served as an indicator for halide concentration inside the liposomes and was used to follow the kinetics of halide flux across the bilayer membranes. The observed permeability coefficients ranged from 10(-9) to 10(-7) cm/s and increased as the bilayer thickness was reduced. Bromide was found to permeate approximately six times faster than chloride through bilayers of identical thickness, and iodide permeated three to four times faster than bromide. The dependence of the halide permeability coefficients on bilayer thickness and on ionic size were consistent with permeation of hydrated ions by a solubility-diffusion mechanism rather than through transient pores. Halide permeation therefore differs from that of a monovalent cation such as potassium, which has been accounted for by a combination of the two mechanisms depending on bilayer thickness.

Permeation of protons, potassium ions, and small polar molecules through phospholipid bilayers as a function of membrane thickness

Two mechanisms have been proposed to account for solute permeation of lipid bilayers. Partitioning into the hydrophobic phase of the bilayer, followed by diffusion, is accepted by many for the permeation of water and other small neutral solutes, but transient pores have also been proposed to account for both water and ionic solute permeation. These two mechanisms make distinctively different predictions about the permeability coefficient as a function of bilayer thickness. Whereas the solubility-diffusion mechanism predicts only a modest variation related to bilayer thickness, the pore model predicts an exponential relationship. To test these models, we measured the permeability of phospholipid bilayers to protons, potassium ions, water, urea, and glycerol. Bilayers were prepared as liposomes, and thickness was varied systematically by using unsaturated lipids with chain lengths ranging from 14 to 24 carbon atoms. The permeability coefficient of water and neutral polar solutes displayed a modest dependence on bilayer thickness, with an approximately linear fivefold decrease as the carbon number varied from 14 to 24 atoms. In contrast, the permeability to protons and potassium ions decreased sharply by two orders of magnitude between 14 and 18 carbon atoms, and leveled off, when the chain length was further extended to 24 carbon atoms. The results for water and the neutral permeating solutes are best explained by the solubility-diffusion mechanism. The results for protons and potassium ions in shorter-chain lipids are consistent with the transient pore model, but better fit the theoretical line predicted by the solubility-diffusion model at longer chain lengths.