Endotoxin impairs the human pacemaker current If

LPSs trigger the development of sepsis by gram-negative bacteria and cause a variety of biological effects on host cells, including alterations on ionic channels. Because heart rate variability is reduced in human sepsis and endotoxemia, we hypothesized that LPS affects the pacemaker current I(f) in human heart, which might--at least in part--explain this phenomenon. Isolated human myocytes from right atrial appendages were incubated for 6 to 10 h with LPS (1 and 10 microg/mL) and afterwards used to investigate the pacemaker current I(f). I(f) was measured with the whole-cell patch-clamp technique (at 37 degrees C). Incubation of atrial myocytes with 10 microg/mL LPS was found to significantly impair I(f) by suppressing the current at membrane potentials positive to -80 mV and slowing down current activation, but without effecting maximal current conductance. Furthermore, in incubated cells (10 microg/mL), the response of I(f) to [beta]-adrenergic stimulation (1 microM isoproterenol) was significantly larger compared with control cells (shift of half-maximal activation voltage to more positive potentials amounted to -10 and -14 mV in untreated and treated cells, respectively). Simulations using a spontaneously active sinoatrial cell model demonstrated that LPS-induced I(f) impairment reduced the responsiveness of the model cell to fluctuations of autonomic input. This study showed a direct impact of LPS on the cardiac pacemaker current I(f). The LPS-induced I(f) impairment may contribute to the clinically observed reduction in heart rate variability under septic conditions and in cardiac diseases such as heart failure, where endotoxin can be of pathophysiological relevance.     

Increased IgE-dependent mast cell activation and anaphylactic responses in mice lacking the calcium-activated nonselective cation channel TRPM4

Mast cells are key effector cells in allergic reactions. Aggregation of the receptor FcepsilonRI in mast cells triggers the influx of calcium (Ca(2+)) and the release of inflammatory mediators. Here we show that transient receptor potential TRPM4 proteins acted as calcium-activated nonselective cation channels and critically determined the driving force for Ca(2+) influx in mast cells. Trpm4(-/-) bone marrow-derived mast cells had more Ca(2+) entry than did TRPM4(+/+) cells after FcepsilonRI stimulation. Consequently, Trpm4(-/-) bone marrow-derived mast cells had augmented degranulation and released more histamine, leukotrienes and tumor necrosis factor. Trpm4(-/-) mice had a more severe IgE-mediated acute passive cutaneous anaphylactic response, whereas late-phase passive cutaneous anaphylaxis was not affected. Our results establish the physiological function of TRPM4 channels as critical regulators of Ca(2+) entry in mast cells.     

The heterozygous LMNA mutation p.R471G causes a variable phenotype with features of two types of familial partial lipodystrophy

We report on a novel LMNA mutation (p.R471G) in a proband affected by a syndrome comprising partial lipodystrophy, insulin-resistant diabetes, acanthosis nigricans, liver steatosis, muscle weakness, and contractures. This phenotype has features of both types 1 and 2 familial partial lipodystrophy. The sister and father of the proband had the same mutation. The sister was more mildly affected and the father was apparently unaffected, demonstrating variable expressivity and reduced penetrance for this mutation.     

Oxidant-induced cardiomyocyte injury: identification of the cytoprotective effect of a dopamine 1 receptor agonist using a cell-based high-throughput assay

Myocyte injury due to myocardial reperfusion injury plays a crucial role in the pathogenesis of acute myocardial infarction even after successful coronary revascularization. Identification of compounds that reduce reperfusion-associated myocyte death is important. Therefore, we developed an in vitro model of myocardial reperfusion injury in H9c2 rat cardiomyocytes and applied a cell-based high-throughput approach to screen a standard library of pharmacologically active compounds (LOPAC) in order to identify drugs with cardioprotective effects. Oxidative stress was induced with hydrogen peroxide (H2O2) treatment, which resulted in approximately 50% reduction in cell viability. Test compounds were added at a 3-microM final concentration as a pretreatment or in a delayed fashion (30 min after the peroxide challenge in order to imitate pharmacological treatment following angioplasty). Cells were cultured for 3 or 24 h. Viability was quantitated with the methylthiazolyldiphenyl-tetrazolium bromide method. Cytotoxicity and cytoprotection were also evaluated by measuring the lactate dehydrogenase activity in the cell culture supernatant. The screening identified a number of compounds with cytoprotective action, including molecules that are known to interfere with components of DNA repair and cell cycle progression, e.g. poly(ADP-ribose) polymerase (PARP) inhibitors, topoisomerase inhibitors, and cyclin dependent kinase inhibitors, or reduce energy consumption by interfering with cardiac myofilament function. A number of dopamine D1 receptor agonists also provided significant cytoprotection at 3 h, but only three of them showed a similar effect at 24 h: chloro- and bromo-APB and chloro-PB hydrobromide. Chloro-APB hydrobromide significantly reduced peroxide-induced PARP activation in the myocytes independently of its action on dopamine D1 receptors, but lacked PARP inhibitor capacity in a cell-free PARP assay system. In conclusion, the pattern of cytoprotective drugs identified in the current assay supports the overall validity of our model system. The findings demonstrate that cytoprotective agents, including novel indirect inhibitors of cellular PARP activation can be identified with the method, chloro-APB hydrobromide being one such compound. The current experimental setting can be employed for cell-based high-throughput screening of various compound libraries.     

Thoracic organ transplantation may not increase the risk of bacterial transmission in intensive care units

A transmission study was performed to investigate whether organ recipients suffer more transmissions of bacteria than do non-transplanted patients. We chose enterococci for molecular typing because of their high prevalence, transmissibility, and predominance in causing nosocomial infections. Patients staying longer than 48h in a cardiovascular surgery intensive care unit (ICU) were included in our one-year prospective cohort study. Enterococci identified from clinical or surveillance isolates were collected and typed by PFGE. Episodes of transmission were defined by the identification of genetically indistinguishable isolates in two or more patients who were treated during overlapping intervals or within a 9-day window period in the same ICU. Risk factor analysis was performed. Out of 585 patients microbiological specimens were cultured from 336 patients. From 187 of these, enterococci were isolated. From 81 patients 186 enterococci isolates were typed. Out of 105 different enterococci strains, 16 cluster strains were detected and 30 episodes of transmissions occurred. The transmission rate was 7.8 per 1000 patient days. No significant association was found between "being cluster member "and "patient organ transplanted" (OR 1.5, CI(95%) 0.58; 3.98, p=0.38) or "patient treated in a single-room only" (OR 1.06, CI(95%) 0.36;3, 12, p=0.91), respectively. In contrast, "being cluster member" was associated with a prolonged length of stay (OR per additional days of stay 1.05, CI(95%) 1.01-1.09, p<0.01). Thoracic organ transplantation was not found to be a risk factor for bacterial transmission, but transmission was associated with a prolonged length of stay.