Cooperative Cargo Transport by Several Molecular Motors

The transport of cargo particles which are pulled by several molecular motors in a cooperative manner is studied theoretically. The transport properties depend primarily on the maximal number, $N$, of motor molecules that may pull simultaneously on the cargo particle. Since each motor must unbind from the filament after a finite number of steps but can also rebind to it again, the actual number of pulling motors is not constant but varies with time between zero and $N$. An increase in the maximal number $N$ leads to a strong increase of the average walking distance (or run length) of the cargo particle. If the cargo is pulled by up to $N$ kinesin motors, e.g., the walking distance is estimated to be $5^{N-1}/N$ micrometers which implies that seven or eight kinesin molecules are sufficient to attain an average walking distance in the centimeter range. If the cargo particle is pulled against an external load force, this force is shared between the motors which provides a nontrivial motor-motor coupling and a generic mechanism for nonlinear force-velocity relationships. With increasing load force, the probability distribution of the instantenous velocity is shifted towards smaller values, becomes broader, and develops several peaks. Our theory is consistent with available experimental data and makes quantitative predictions that are accessible to systematic in vitro experiments.Comment: 24 pages, latex, 6 figures, includes Supporting Tex

Perspectives of staff nurses of the reasons for and the nature of patient-initiated call lights: an exploratory survey study in four USA hospitals

<p>Abstract</p> <p>Background</p> <p>Little research has been done on patient call light use and staff response time, which were found to be associated with inpatient falls and satisfaction. Nurses' perspectives may moderate or mediate the aforementioned relationships. This exploratory study intended to understand staff's perspectives about call lights, staff responsiveness, and the reasons for and the nature of call light use. It also explored differences among hospitals and identified significant predictors of the nature of call light use.</p> <p>Methods</p> <p>This cross-sectional, multihospital survey study was conducted from September 2008 to January 2009 in four hospitals located in the Midwestern region of the United States. A brief survey was used. All 2309 licensed and unlicensed nursing staff members who provide direct patient care in 27 adult care units were invited to participate. A total of 808 completed surveys were retrieved for an overall response rate of 35%. The SPSS 16.0 Window version was used. Descriptive and binary logistic regression analyses were conducted.</p> <p>Results</p> <p>The primary reasons for patient-initiated calls were for toileting assistance, pain medication, and intravenous problems. Toileting assistance was the leading reason. Each staff responded to 6 to 7 calls per hour and a call was answered within 4 minutes (estimated). 49% of staff perceived that patient-initiated calls mattered to patient safety. 77% agreed that that these calls were meaningful. 52% thought that these calls required the attention of nursing staff. 53% thought that answering calls prevented them from doing the critical aspects of their role. Staff's perceptions about the nature of calls varied across hospitals. Junior staff tended to overlook the importance of answering calls. A nurse participant tended to perceive calls as more likely requiring nursing staff's attention than a nurse aide participant.</p> <p>Conclusions</p> <p>If answering calls was a high priority among nursing tasks, staff would perceive calls as being important, requiring nursing staff's attention, and being meaningful. Therefore, answering calls should not be perceived as preventing staff from doing the critical aspects of their role. Additional efforts are necessary to reach the ideal or even a reasonable level of patient safety-first practice in current hospital environments.</p

The effects of xylanase on grower pig performance, concentrations of volatile fatty acids and peptide YY in portal and peripheral blood

Non-starch polysaccharides (NSP) present in wheat and barley can act as anti-nutrients leading to an increase in digesta viscosity and a reduction in nutrient digestibility. Xylanase, an NSP-degrading enzyme, has been shown to increase nutrient digestibility in pigs. The objectives of this study were: (1) to identify the optimum inclusion level of xylanase in grower pig diets by measuring the effect of increasing enzyme levels on growth performance, the concentration of volatile fatty acids (VFA) and peptide YY concentration in portal and peripheral blood of grower pigs and (2) to increase our understanding of the interrelationships between xylanase inclusion, VFA production and peptide YY secretion. A total of 512 grower pigs ((Large White×Landrace)×MAXGRO) were allocated to pens creating 32 replicates of four pigs per pen per treatment. Pigs were allocated to trial weighing 14.2±0.31 kg and remained on trial until ~41.5±3.31 kg. The experiment was a dose response design with four inclusion levels (0, 8000, 16 000 or 32 000 BXU/kg) of xylanase (Econase XT). Diets were cereal-based wheat, barley mix formulated to meet or exceed the nutrient requirements of grower pigs. Body weight and feed intake were recorded to calculate growth performance. Pen faecal samples were collected to estimate DM, organic matter (OM) and crude fibre (CF) apparent total-tract digestibility. At the end of the trial 16 pigs per treatment were euthanised by schedule 1 procedures. Peripheral and portal blood samples were collected for peptide YY and VFA analysis. The addition of xylanase to the diet had no effect on growth performance, DM, OM or CF total-tract digestibility; however, xylanase tended to have a quadratic effect on ileum pH with higher pH values recorded for pigs fed a diet supplemented with 8000 and 16 000 BXU/kg xylanase (P<0.1). Xylanase had no effect on peptide YY levels or VFA concentration. Total VFA concentration was higher in portal compared with peripheral blood (P<0.05). In conclusion, the addition of xylanase had no effect on grower pig performance, nutrient digestibility, VFA concentration or peptide YY concentration when fed up to 32 000 BXU/kg over a 35-day period. Pig performance was good for all treatments throughout the trial suggesting that diet quality was sufficient thus there were no beneficial effects of adding xylanase

Malignant hypertension and acute aortic dissection associated with caffeine-based ephedra-free dietary supplements: a case report

The use of weight loss dietary supplements is prevalent in the United States, and over the past decade, there has been tremendous growth of the use of these products. It is well documented that ephedra-based products are associated with various cardiovascular adverse effects. With new restrictions placed on such products, companies are now manufacturing caffeine-based ephedra-free herbal supplements. We present the case of 36-year old, previously healthy female who developed malignant hypertension and aortic dissection while taking various caffeine-based dietary supplements. Given the lack of research studies in regards to their safety and efficacy, judicious care should be taken with the use of dietary supplements, including those designated as ephedra-free

Effect of oral progesterone and caffeine at the end of gestation on farrowing duration and piglet growth and survival

The profitability of pig production is constrained by high incidences of peri-parturient and pre-weaning piglet mortality. Supplementing sows with either progesterone or caffeine during the last week of gestation can reduce stillbirths and improve piglet performance. However, the consequences of combining these two substances has not been investigated. The aim of the current study was to determine the effect of oral supplementation of sows with progesterone (regumate) and caffeine at the end of gestation on the timing and progression of farrowing, as well as piglet survival and growth to weaning. From days 111 to 113 of gestation, 20 Large White pregnant sows (parity 3.0±0.45) received 5 ml of Regumate Porcine (0.4 w/v oral solution; MSD Animal Health) daily on top of their morning ration. Sows were stratified according to parity and predicted farrowing date, and allocated at random to receive a diet supplemented with either 0 g caffeine/kg diet (CONT) or 2.4 g of caffeine/kg diet (CAFF) from day 113 of gestation until parturition (n=10 sows/treatment). Treatment did not affect total litter size; however, CONT sows gave birth to more live and fewer dead piglets compared with CAFF sows; 14.5±0.73 v. 11.7±1.03 and 0.7±0.20 v. 3.2±0.77; P<0.05). Mean, minimum and maximum piglet birthweight were unaffected by treatment. Compared with the control, caffeine increased the proportion of piglets with a birthweight <1 kg (0.16±0.05 v. 0.05±0.02; P=0.072) and decreased the proportion of live born piglets surviving to day 5 postpartum (0.77±0.06 v. 0.90±0.02; P<0.05) and to weaning (0.74±0.06 v. 0.90±0.02; P<0.05). Overall, the current data provided the first evidence that caffeine supplementation of sows receiving progesterone to prevent premature farrowing impaired piglet survival during, and shortly after parturition. This negative outcome may be linked to extended farrowing durations and an increase in the proportion of very light piglets at birth. These data provide compelling, albeit preliminary, evidence that caffeine and progesterone should not be used together at the end of gestation