The dependence of twitch relaxation on sodium ions and on internal Ca2+ stores in voltage clamped frog atrial fibres

Frog heart relaxation was analyzed under voltage clamp conditions as the tension decay observed after the membrane potential had been returned to its resting value. The tension decayed exponentially with a time constant of 188±3.8 ms SEM. The relaxation rate decreased with the external Na concentration. It fell to about one tenth in a Na-free solution. Increasing the intracellular Na-content by an application of veratrine also decreased the relaxation rate. Thus relaxation seems dependent on the Na gradient. The relaxation rate decreased within one second upon switching from a high to a low Na-containing solution. The relaxation rate reached a minimum before rising slightly to a new steady state value. This rebound may reflect the partial recovery of the Na gradient since a fast variation in [Na]_i follows alteration of [Na]_o. Mn and La ions also slowed relaxation. In a Na-free solution, adrenaline accelerated tension decay, an effect not noticeable in frog heart contained in Ringer solution. Other cAMP-promoting agents, such as dibutyryl-cAMP and aminophylline, also increased relaxation rate.It is concluded that in frog myocardium, part of the decrease of the intracellular Ca²⁺-concentration which occurs during each cardiac cycle could be dependent on a Na–Ca exchange mechanism. The relative importance of this mechanism, versus internal Ca sequestration, in the relaxation of tension may well be greater in contractile tissues whose cells have a large surface/volume ratio.     

Overloaded training increases exercise-induced oxidative stress and damage.

We hypothesized that overloaded training (OT) in triathlon would induce oxidative stress and damage on muscle and DNA. Nine male triathletes and 6 male sedentary subjects participated in this study. Before and after a 4-week OT, triathletes exercised for a duathlon. Blood ratio of reduced vs. oxidized glutathione (GSH/GSSG), plasma thiobarbituric acid reactive substances (TBARS), leukocyte DNA damage, creatine kinase (CK), and CK-MB mass in plasma, erythrocyte superoxide dismutase (SOD) activity, erythrocyte and plasma glutathione peroxidase (GSH-Px) activities, and plasma total antioxidant status (TAS) were measured before and after OT in pre- and postexercise situations. Triathletes were overloaded in response to OT. In rest conditions, OT induced plasma GSH-Px activity increase and plasma TAS decrease (both p < 0.05). In exercise conditions, OT resulted in higher exercise-induced variations of blood GSH/GSSG ratio, TBARS level (both p < 0.05), and CK-MB mass (p < 0.01) in plasma; and decreased TAS response (p < 0.05). OT could compromise the antioxidant defense mechanism with respect to exercise-induced response. The resulting increased exercise-induced oxidative stress and further cellular susceptibility to damage needs more study.     

Pharmacokinetic consequences of a citalopram treatment discontinuation.

In this pilot study, the pharmacokinetics of citalopram (CIT) were examined in five hospitalized depressed patients after an abrupt discontinuation of a treatment with 40 mg/d of this selective serotonin reuptake inhibitor (SSRI). During the 8-day study period, clinical ratings were regularly carried out. Between days 5 and 8, the patients were treated with clomipramine (75 mg/d). The enantiomers of CIT and its metabolites, demethyl-CIT (DCIT) and CIT-propionic acid derivative (CIT-PROP), were measured repeatedly from day 0 to day 8 by a stereoselective high-performance liquid chromatography (HPLC) procedure. The following drug plasma half-lives were measured (means +/- SD): R-CIT: 66+/-11 h; S-CIT: 42+/-13 h; R-DCIT: 228+/-148 h; S-DCIT: 93+/-35 h; R-CIT-PROP: 82+/-31 h; S-CIT-PROP: 186+/-93 h.     

Associations Between Environmental Characteristics and Active Commuting to School Among Children: a Cross-sectional Study

Background

Active commuting to school can contribute to active living among children, and environmental characteristics might be related to transportation mode to school.

Purpose

The purpose of this study is to explore the association between physical and social environmental characteristics in the home, neighborhood, and school environment and walking and bicycling to school.

Method

Data were collected among parents (n?=?5,963) of children of primary schools in four Dutch cities. Parents reported mode of transportation to school, and individual, home environmental, neighborhood, and school environmental characteristics. Social as well as physical characteristics were included for the home and neighborhood environment. Multilevel multinomial logistic regression analyses were conducted to quantify the association between environmental characteristics and walking and bicycling to school.

Results

Three quarter of all children usually commute to school by active transportation, but age and distance from home to school were important prerequisites. Besides home environmental characteristics, lower neighborhood socioeconomic status was negatively associated with walking [odds ratio (OR)?=?0.51] and bicycling (OR?=?0.86). Perceived social safety was positively related to walking and bicycling (OR?=?1.04 for both), as was perceived social cohesion (OR?=?1.04 and 1.02 for walking and bicycling). Living in the city center was positively associated with walking (OR?=?1.91), whereas living in a city green neighborhood was negatively associated with walking and bicycling (OR?=?0.48 and 0.76, respectively). Traffic safety as perceived by school boards was positively associated with bicycling (OR?=?1.25).

Conclusion

This study shows that there is a relation between several characteristics in the home, neighborhood, and school environment and walking and bicycling to school among Dutch primary school children. Especially the social neighborhood characteristics were related to active commuting. Therefore, apart from providing a physical infrastructure that facilitates safe and convenient active commuting to school, policy makers should be aware of opportunities to facilitate active commuting by social initiatives in local communities.     

Hockey Games and the Incidence of ST-Elevation Myocardial Infarction

Background

The association between diagnosed acute ST-elevation myocardial infarction (STEMI) and hockey games in the Canadian population is unknown.

Guiding Breast-Conserving Surgery in Patients After Neoadjuvant Systemic Therapy for Breast Cancer: A Comparison of Radioactive Seed Localization with the ROLL Technique

Background

Radioguided occult lesion localization (ROLL) with technetium-99 m colloid (ROLL-^99mTc) is commonly used to perform breast-conserving surgery in patients with nonpalpable breast tumors. Radioactive seed localization is a relatively new technique that localizes the tumor with a radioactive iodine-125 (¹²⁵I) seed. The feasibility and outcome of these techniques after neoadjuvant systemic treatment has not been widely investigated.

Methods

All patients treated with neoadjuvant systemic treatment between 2007 and 2010 in the Netherlands Cancer Institute who underwent breast-conserving surgery with the ROLL-^99mTc technique (n = 83) or with ¹²⁵I seed localization (n = 71) were analyzed. The weight of the resected specimen, the margins, and the percentage of patients requiring a second surgical intervention as a result of positive margins were assessed.

Results

Patient and tumor characteristics and systemic treatment regimens were comparable between both groups. The median weight of the resected specimen (53 vs. 48 g), the median smallest margin (3.5 vs. 3.0 mm), and the risk for additional surgery for incomplete resections (7 vs. 8 %) did not differ significantly between patients treated with the ROLL-^99mTc technique and ¹²⁵I seed localization.

Conclusions

The ROLL-^99mTc technique and ¹²⁵I seed localization demonstrate comparable results when used to perform breast-conserving surgery after neoadjuvant systemic treatment. Because ¹²⁵I seed localization does not require additional radiological localization shortly before surgery, it simplifies surgery scheduling. Therefore, we prefer ¹²⁵I seed localization to perform breast-conserving surgery after neoadjuvant systemic treatment.     

Early Assessment of Axillary Response with 18F-FDG PET/CT during Neoadjuvant Chemotherapy in Stage II–III Breast Cancer: Implications for Surgical Management of the Axilla

Background

If all initially node-positive patients undergo axillary lymph node dissection (ALND) after neoadjuvant chemotherapy (NAC), overtreatment may occur in patients with complete response. Positron emission tomography–computed tomography (PET/CT) during NAC may predict axillary response and select patients appropriate for less invasive treatment after NAC. We evaluated the value of sequential ¹⁸F fluorodeoxyglucose (FDG) PET/CTs during NAC for axillary response monitoring in stage II–III breast cancer.

Methods

A total of 219 PET/CTs were performed in 80 patients with cytology-proven, node-positive disease at baseline (PET/CT1, n = 80) and twice during NAC (PET/CT2 n = 62, PET/CT3, n = 77). The relative changes in maximum standardized uptake value (SUV_max) of axillary nodes were examined for their ability to assess pathological response. All patients underwent ALND after chemotherapy, and complete axillary response (pCR), defined as absence of isolated tumor cells and of micro- and macrometastases, served as the reference standard.

Results

A total of 32 (40 %) patients experienced axillary pCR. The relative decrease in SUV_max was significantly higher in patients with pCR than in those without, both on PET/CT2 (p < 0.001) and PET/CT3 (p = 0.025). The area under the receiver operating characteristic curve values for PET/CT2 and PET/CT3 were 0.80 (95 % confidence interval 0.68–0.92) and 0.65 (95 % confidence interval 0.52–0.79), respectively. A relative decrease of ≥60 % on PET/CT2 had an excellent specificity (35 of 37, 95 %), a high positive predictive value (12 of 14, 86 %), and a sensitivity of 48 %—that is, it accurately identified histologic pCR in 12 of 25 patients with disease that responded to therapy.

Conclusions

¹⁸F-FDG PET/CT early during NAC is useful for axillary response monitoring in cytology-proven node-positive breast cancer because it identifies pathological response, thus permitting ALND to be spared.