Biomedical subjects

R Häsler

Publications and source records attributed to R Häsler.

7 recordsLinked to original sources

PubMed2006

Acquired chemoresistance in pancreatic carcinoma cells: induced secretion of IL-1beta and NO lead to inactivation of caspases.

Pancreatic cancer exhibits profound chemoresistance resulting either from pre-existing (intrinsic) mechanisms, or from anticancer drug treatment itself (acquired chemoresistance). To identify molecular alterations leading to acquired chemoresistance, the chemosensitive pancreatic carcinoma cell line PT45-P1 was exposed to low-dose treatment with etoposide for 6 weeks. Afterwards, these cells (PT45-P1res) were much more resistant to high-dose treatment with anticancer drugs than parental cells. Among several differentially expressed genes in PT45-P1res cells, IL-1beta was most significantly upregulated, a finding in line with our previous observation that IL-1beta accounts for intrinsic chemoresistance of pancreatic carcinoma cells. Elevated IL-1beta expression in PT45-P1res cells was confirmed by real-time PCR and ELISA, and treatment with the IL-1 receptor antagonist restored drug-induced apoptosis. The increased IL-1beta secretion was accompanied by an elevated formation of nitric oxide (NO) and a NO-dependent inhibition of the etoposide-induced caspase-3/-7/-8/-9 activity. Caspase activation was restored either by the iNOS inhibitor 1400W, the reducing agent dithiothreitol or the IL-1 receptor antagonist, resulting in greater sensitivity towards anticancer drug treatment. Conversely, IL-1beta or the NO-donor SNAP decreased caspase activation and apoptosis in etoposide-treated PT45-P1 cells. These data confirm IL-1beta and NO as determinants of chemoresistance in pancreatic cancer, and indicate that the intrinsic and acquired chemoresistance rely to some extent on common molecular targets beneficial for improved therapeutical strategies.

Antineoplastic Agents↗

PubMed2002

Midday stomatal closure in Norway spruce--reactions in the upper and lower crown.

We used local microclimatic conditions and twig sap flow rates to interpret midday stomatal closure in the canopies of two 250-year-old Norway spruce (Picea abies (L.) Karst.) trees at a subalpine site in the Swiss Alps (1,650 m a.s.l.). Both trees showed midday stomatal closure on most clear summer days, despite the permanently wet soil. We used a modified Penman-Monteith formula to simulate potential transpiration of single twigs (ET(T)) based on high-resolution temporal and spatial microclimate data obtained both inside and outside the crowns. Comparison of calculated ET(T) values and measured twig sap flow rates enabled us to pinpoint the occurrence of midday stomatal closure and the microclimatic conditions present at that time. We found that vapor pressure deficit (and for upper-crown twigs, ET(T)) largely explained the timing of initial midday stomatal closure but gave no explanation for the different patterns of stomatal behavior after initial closure in upper- and lower-crown twigs. After the initial stomatal closure, upper-crown twigs maintained high transpiration rates by continuously regulating stomatal aperture, whereas stomatal aperture decreased rapidly in lower-crown twigs and did not increase later in the day. Midday stomatal closure in lower-crown twigs occurred on average 1 h later than in upper-crown twigs. However, the microclimate at the time of initial stomatal closure was similar at both crown locations except that lower-crown twigs received significantly less solar radiation than upper-crown twigs both at the time of initial stomatal closure and afterwards. High rates of sap flow in twigs did not always lead to stomatal closure and therefore could not explain the phenomenon. We conclude that stomatal conductance can be modeled accurately only when both local microclimatic conditions and tree water status are known. Further, we hypothesize that both the quantity and quality of light play an important role in the reopening of closed stomata during the day.

Biomass↗

PubMed2001

Link between diurnal stem radius changes and tree water relations.

Internal water reserves are depleted and replenished daily, not only in succulent plants, but also in trees. The significance of these changes in tissue water storage for tree water relations was investigated by monitoring diurnal fluctuations in stem radius. In 6-year-old potted Norway spruce (Picea abies (L.) Karst.) trees, whole-tree transpiration rate (T), sap flow at the stem base and fluctuations in stem radius were measured at 10-min intervals over eight successive weeks. The dynamics of diurnal water storage in relation to the daily course of water movement was simulated and the contribution of stored water to T quantified. The finding that, in P. abies, the course of bark water content is linearly coupled to stem radius fluctuations provided the basis for linking stem radius changes to a functional flow and storage model for tree water relations. This model, which consists of physical functions only and is driven by a single input variable (T), accurately simulates the diurnal course of changes in stem radius and water storage of the tree crown and stem. It was concluded that fluctuations were mainly determined by the course of transpiration. The availability of soil water and the degree to which storage tissues were saturated were also factors affecting the diurnal course of stem radius changes. Internally stored water contributed to daily transpiration even in well-watered trees, indicating that stored water plays an important role not only during periods of drought, but whenever water transport occurs within the tree. Needle and bark water reserves were most heavily depleted during transpiration. Together they supplied approximately 10% of daily T on sunny days, and up to 65% on cloudy days. On a daily basis, the crown (mainly needles) contributed approximately eight times more water to T than the stem (mainly bark). The depletion of the two storage pools and the water movements observed in the trees always occurred in the same sequence. In the morning, T first caused a depletion of the water stored in the crown. It then caused depletion of bark storage tissues at ever increasing distances from the needles. Up to 75% of the transpired water could be withdrawn from storage tissues when the increase in T reached a maximum.

Circadian Rhythm↗

PubMed2001

Dynamics of water storage in mature subalpine Picea abies: temporal and spatial patterns of change in stem radius.

Internal water reserves in bark and foliage of trees contribute to transpiration (T) and play an essential role in optimizing water transport by buffering extreme peaks of water consumption. We examined patterns of stem shrinkage and their relationship to tree water dynamics. We measured fluctuations in root radius and stem radius at different stem heights, T of twigs at the top of the crown and sap flow velocities in stem sections of mature subalpine Norway spruce (Picea abies (L.) Karst.) trees over 2 years. The output of each sensor was coupled by physical functions to a mechanistic flow and storage model of tree water relations. The data verified the model-predicted lag in water storage depletion in response to the onset of transpiration and the lag increased with increasing distance from the crown periphery. Between the crown and stem base, the delay ranged from a few minutes to several hours, depending on microclimatic conditions and tree water status. Stem volume changes were proportional to the amount of water exchanged between the elastic tissues of the bark and the rigid xylem, indicating that the "peristaltic" wave of stem contraction along the flow path represented depletion of water stored in bark. On a daily basis, stems lost between 0.2 and 0.5% of their volume as a result of bark dehydration, corresponding to about 2 to 5 l of water. This water contributed directly to T. According to the model based on hydraulic principles, there are three main components underlying the dynamics of water storage depletion: flow resistance, storage capacities of needles and bark, and T of each tree section. The resistances and capacities were proportional to the response delay, whereas T in the lower parts of the tree was inversely proportional. The pattern of T within the crown depended on water intercepted by the branches. Because of these weather-dependent factors, there was no time constant for the response delay along the flow path. Nevertheless, the upper crown and the root section tended to have longer response delays per meter of flow path than the stem. The diurnal course of stem radius fluctuations represents the sum of all external and internal conditions affecting tree water relations; stem radius fluctuations, therefore, provide a sensitive measure of tree water status.

Picea↗

PubMed2000

Role of climate, crown position, tree age and altitude in calculated ozone flux into needles of Picea abies and Pinus cembra: a synthesis.

Ozone (O(3)) flux into Norway spruce (Picea abies) and cembran pine (Pinus cembra) needles was estimated under ambient conditions at six rural sites between 580 and 1950 m a.s.l. We also assessed age-related differences in O(3) flux by examining changes in leaf conductance across the life span of Norway spruce. At the leaf level O(3) flux into the needles was effectively controlled by stomatal conductance and, hence by factors such as temperature, irradiance and humidity, which control stomatal conductance. Seasonal variations in O(3) flux were mainly attributed to the course of the prevailing temperature. During the growing season, however, data have emphasised leaf-air vapour pressure difference as the environmental factor most likely to control stomatal conductance and O(3) flux into the needles. In the sun crown stomatal conductance averaged over the growing season decreased with increasing tree age from 42.0+/-3.5 mmol O(3) m(-2) s(-1) in 17-year-old trees to 7.1+/-1.0 mmol O(3) m(-2) s(-1) in 216-year-old trees, indicating that O(3) concentration in the substomatal cavities is higher in young than in old trees. Independent from tree age stomatal conductance and O(3) flux were approximately 50% lower in shade needles as compared to sun-exposed needles. Stomatal conductance was also greater in the current flush (24+/-5.6 mmol O(3) m(-2) s(-1)) and in 1-year old needles (16+/-4 mmol O(3) m(-2) s(-1)) than in older needle age classes (12+/-1 mmol O(3) m(-2) s(-1), averaged across the four older needle age classes). In trees similar in age (60-65 years old) average O(3) flux into sun needles increased from 0.55+/-0.36 nmol m(-2) s(-1) at the valley floor to 0.9 nmol m(-2) s(-1) in 1950 m a.s.l. Cumulative O(3) uptake during the vegetation period increased from 11.4+/-1.7 mol m(-2) in the valley to 14 mol m(-2) at the alpine timberline. Although stomatal conductance provides the principal limiting factor for O(3) flux, additional field research is necessary in order to improve our understanding concerning the quantitative 'physiological threshold dose' which internally can be active and can have adverse effects of O(3) on forest trees.

Journal Article↗

PubMed2000

The effect of a maxillary lip bumper on tooth positions.

The effect of the use of a lip bumper with anterior vestibular shields on the maxilla was studied in twenty-two 9-14-year-old children with a space deficiency in the maxillary dental arch. The lip bumper was used for 1 year. The effect of the treatment was evaluated from dental casts and profile cephalograms made before and after treatment. Both the width of the maxillary dental arch at the premolars and the length of the arch increased significantly by about 2 mm. The effect of the treatment on the antero-posterior position of the first molars was small. In one subject the molar was distalized 2.8 mm. The average effect was, however, a reduction in the anterior movement of the molar within the face by about 0.5 mm, i.e. the maxilla moved anteriorly 1 mm, but the molar only 0.4 mm. No skeletal effects were found when the group of subjects treated with a lip bumper was compared with a reference sample of untreated individuals. The main effects of a maxillary lip bumper thus seem to be a widening of the dental arch across the premolars, a moderate increase in arch length due to eruption and slight proclination of the incisors, and moderate distal tipping of the first molars.

Adolescent↗

PubMed1997

A clinical comparison of the rate of maxillary canine retraction into healed and recent extraction sites--a pilot study.

The rate of movement of the maxillary canines into the healed or recent extraction alveolus of the first premolar was measured in 22 patients aged 10-27 years. On one side of the dental arch, the first premolar was extracted. After a median time of 86 days, the contralateral first premolar was extracted and the distalization of both canines started using Gjessing canine retraction springs. The experiment was ended when one of the two canines had been sufficiently distalized. Recordings of the positions of the canines at the beginning of the study, at the start of the distalization and at the end were made from dental casts and standardized intraoral radiographs. The canine on the recent extraction side moved faster than that on the healed side, but also tipped somewhat more. The reasons for the increased tipping and the faster movement are discussed.

Adolescent↗