Isoenzyme-specific regulation of cardiac Kv1.5/Kvβ1.2 ion channel complex by protein kinase C: central role of PKCβII

The ultrarapidly activating delayed rectifier current, I _Kur, is a main determinant of atrial repolarization in humans. I _Kur and the underlying ion channel complex Kv1.5/Kvβ1.2 are negatively regulated by protein kinase C. However, the exact mode of action is only incompletely understood. We therefore analyzed isoenzyme-specific regulation of the Kv1.5/Kvβ1.2 ion channel complex by PKC. Cloned ion channel subunits were heterologously expressed in Xenopus oocytes, and measurements were performed using the double-electrode voltage-clamp technique. Activation of PKC with phorbol 12-myristate 13-acetate (PMA) resulted in a strong reduction of Kv1.5/Kvβ1.2 current. This effect could be prevented using the PKC inhibitor staurosporine. Using the bisindolylmaleimide Ro-31-8220 as an inhibitor and ingenol as an activator of the conventional PKC isoforms, we were able to show that the Kv1.5/Kvβ1.2 ion channel complex is mainly regulated by conventional isoforms. Whereas pharmacological inhibition of PKCα with HBDDE did not attenuate the PMA-induced effect, current reduction could be prevented using inhibitors of PKCβ. Here, we show the isoform β_II plays a central role in the PKC-dependent regulation of Kv1.5/Kvβ1.2 channels. These results add to the current understanding of isoenzyme-selective regulation of cardiac ion channels by protein kinases.     

Short-term effects of noisy pressure support ventilation in patients with acute hypoxemic respiratory failure

Introduction

This study aims at comparing the very short-term effects of conventional and noisy (variable) pressure support ventilation (PSV) in mechanically ventilated patients with acute hypoxemic respiratory failure.

Methods

Thirteen mechanically ventilated patients with acute hypoxemic respiratory failure were enrolled in this monocentric, randomized crossover study. Patients were mechanically ventilated with conventional and noisy PSV, for one hour each, in random sequence. Pressure support was titrated to reach tidal volumes approximately 8 mL/kg in both modes. The level of positive end-expiratory pressure and fraction of inspired oxygen were kept unchanged in both modes. The coefficient of variation of pressure support during noisy PSV was set at 30%. Gas exchange, hemodynamics, lung functional parameters, distribution of ventilation by electrical impedance tomography, breathing patterns and patient-ventilator synchrony were analyzed.

Results

Noisy PSV was not associated with any adverse event, and was well tolerated by all patients. Gas exchange, hemodynamics, respiratory mechanics and spatial distribution of ventilation did not differ significantly between conventional and noisy PSV. Noisy PSV increased the variability of tidal volume (24.4 ± 7.8% vs. 13.7 ± 9.1%, P <0.05) and was associated with a reduced number of asynchrony events compared to conventional PSV (5 (0 to 15)/30 min vs. 10 (1 to 37)/30 min, P <0.05).

Conclusions

In the very short term, noisy PSV proved safe and feasible in patients with acute hypoxemic respiratory failure. Compared to conventional PSV, noisy PSV increased the variability of tidal volumes, and was associated with improved patient-ventilator synchrony, at comparable levels of gas exchange.

Trial registration

ClinicialTrials.gov, {"type":"clinical-trial","attrs":{"text":"NCT00786292","term_id":"NCT00786292"}}NCT00786292     

Risk factors for prophylactic proximal aortic replacement in the current era

Background

Decision-making in aortic aneurysm involves careful weighing of spontaneous prognosis and operative risk. There is limited recent information regarding operative risk and risk factors using current surgical strategies.

Methods

From 1998 to 2010, 1,221 patients (60 ± 15 years, 67 % male) underwent elective proximal aortic replacement (286 ascending aortic replacement, 699 concomitant root and 387 concomitant arch replacement). Additional cardiac procedures were necessary in 48 %. Previous cardiovascular operations had been performed in 9.6 % (aortic valve 6.3 %, ascending aorta 2.9 %, coronary artery bypass grafting 2.2 %).

Results

Early mortality was 4.2 % overall; it was 2.6 % for isolated aortic replacement as primary surgery. In patients younger than 70 years (n = 829), mortality was 2.4 % overall and 1.2 % for isolated and primary surgery; it was 7.9 and 6.4 %, respectively, in patients ≥70 years. Mortality was not significantly influenced by root replacement (P = 0.13) or arch replacement (P = 0.27). Multiple logistic regression analysis identified higher age (P < 0.01), chronic aortic dissection (P < 0.01), history of previous cardiovascular surgery (P < 0.01), aortic valve stenosis (P = 0.03), and chronic renal insufficiency (P = 0.03) as independent predictors for increased early mortality. Previous cardiovascular surgery was an independent predictor for increased early mortality in patients younger than 70 (P < 0.01), chronic renal insufficiency was that in patients ≥70 years (P < 0.01).

Conclusions

Using contemporary techniques the risk of proximal aortic replacement is low, in particular in younger patients without previous cardiac or aortic surgery. The risk is increased in older patients, in particular with chronic renal insufficiency. This information should be considered in decision-making for prophylactic aortic replacement.     

Computed tomographic assessment of lung weights in trauma patients with early posttraumatic lung dysfunction

Introduction

Quantitative computed tomography (qCT)-based assessment of total lung weight (M_lung) has the potential to differentiate atelectasis from consolidation and could thus provide valuable information for managing trauma patients fulfilling commonly used criteria for acute lung injury (ALI). We hypothesized that qCT would identify atelectasis as a frequent mimic of early posttraumatic ALI.

Methods

In this prospective observational study, M_lung was calculated by qCT in 78 mechanically ventilated trauma patients fulfilling the ALI criteria at admission. A reference interval for M_lung was derived from 74 trauma patients with morphologically and functionally normal lungs (reference). Results are given as medians with interquartile ranges.

Results

The ratio of arterial partial pressure of oxygen to the fraction of inspired oxygen was 560 (506 to 616) mmHg in reference patients and 169 (95 to 240) mmHg in ALI patients. The median reference M_lung value was 885 (771 to 973) g, and the reference interval for M_lung was 584 to 1164 g, which matched that of previous reports. Despite the significantly greater median M_lung value (1088 (862 to 1,342) g) in the ALI group, 46 (59%) ALI patients had M_lung values within the reference interval and thus most likely had atelectasis. In only 17 patients (22%), M_lung was increased to the range previously reported for ALI patients and compatible with lung consolidation. Statistically significant differences between atelectasis and consolidation patients were found for age, Lung Injury Score, Glasgow Coma Scale score, total lung volume, mass of the nonaerated lung compartment, ventilator-free days and intensive care unit-free days.

Conclusions

Atelectasis is a frequent cause of early posttraumatic lung dysfunction. Differentiation between atelectasis and consolidation from other causes of lung damage by using qCT may help to identify patients who could benefit from management strategies such as damage control surgery and lung-protective mechanical ventilation that focus on the prevention of pulmonary complications.     

Extracorporeal cell therapy of septic shock patients with donor granulocytes: a pilot study

Introduction

Neutrophil granulocytes are the first defense line in bacterial infections. However, granulocytes are also responsible for severe local tissue impairment. In order to use donor granulocytes, but at the same time to avoid local side effects, we developed an extracorporeal immune support system. This first-in-man study investigated whether an extracorporeal plasma treatment with a granulocyte bioreactor is tolerable in patients with septic shock. A further intention was to find suitable efficacy end-points for subsequent controlled trials.

Methods

The trial was conducted as a prospective uncontrolled clinical phase I/II study with 28-day follow-up at three university hospital intensive care units. Ten consecutive patients (five men, five women, mean age 60.3 ± 13.9 standard deviation (SD) years) with septic shock with mean ICU entrance scores of Acute Physiology and Chronic Health Evaluation (APACHE) II of 29.9 ± 7.2 and of Simplified Acute Physiology Score (SAPS) II of 66.2 ± 19.5 were treated twice within 72 hours for a mean of 342 ± 64 minutes/treatment with an extracorporeal bioreactor containing 1.41 ± 0.43 × 10E10 granulocytes from healthy donors. On average, 9.8 ± 2.3 liters separated plasma were treated by the therapeutic donor cells. Patients were followed up for 28 days.

Results

Tolerance and technical safety during treatment, single organ functions pre/post treatment, and hospital survival were monitored. The extracorporeal treatments were well tolerated. During the treatments, the bacterial endotoxin concentration showed significant reduction. Furthermore, noradrenaline dosage could be significantly reduced while mean arterial pressure was stable. Also, C-reactive protein, procalcitonin, and human leukocyte antigen DR (HLA-DR) showed significant improvement. Four patients died in the hospital on days 6, 9, 18 and 40. Six patients could be discharged.

Conclusions

The extracorporeal treatment with donor granulocytes appeared to be well tolerated and showed promising efficacy results, encouraging further studies.

Trial registration

ClinicalTrials.gov Identifier: {"type":"clinical-trial","attrs":{"text":"NCT00818597","term_id":"NCT00818597"}}NCT00818597     

Novel electrophysiological properties of dronedarone: inhibition of human cardiac two-pore-domain potassium (K2P) channels

Dronedarone is currently used for the treatment of paroxysmal and persistent atrial fibrillation (AF). Pharmacological inhibition of cardiac two-pore-domain potassium (K(2P)) channels results in action potential prolongation and has recently been proposed as novel antiarrhythmic strategy. We hypothesized that blockade of human K(2P) channels contributes to the electrophysiological efficacy of dronedarone in AF. Two-electrode voltage clamp and whole-cell patch clamp electrophysiology was used to record K(2P) currents from Xenopus oocytes and Chinese hamster ovary cells. All functional human K(2P) channels were screened for dronedarone sensitivity, revealing significant and concentration-dependent inhibition of cardiac K(2P)2.1 (TREK1; IC(50)?=?26.7?μM) and K(2P)3.1 channels (TASK1; IC(50)?=?18.7?μM) with maximum current reduction of 60.3 and 65.5?% in oocytes. IC(50) values obtained from mammalian cells yielded 6.1?μM (K(2P)2.1) and 5.2?μM (K(2P)3.1). The molecular mechanism of action was studied in detail. Dronedarone block affected open and closed channels. K(2P)3.1 currents were reduced in frequency-dependent fashion in contrast to K(2P)2.1. Mutagenesis studies revealed that amino acid residues implicated in K(2P)3.1 drug interactions were not required for dronedarone blockade. The class III antiarrhythmic drug dronedarone targets multiple human cardiac two-pore-domain potassium channels, including atrial-selective K(2P)3.1 currents. K(2P) current inhibition by dronedarone represents a previously unrecognized mechanism of action that extends the multichannel blocking profile of the drug.