No abstract

We have investigated changes in plasma-membrane fluidity in relation to NaCl concentrations in yeasts and yeast-like fungi that were isolated from either subglacial ice or hypersaline waters. In both of these natural environments, these organisms are exposed to low water activity, due to either high NaCl concentrations or low temperatures. Our data indicate that the fluidity of the plasma membrane can be used as an indicator of fitness for survival in extreme environments. Fungi that can survive in such extreme environments, such as Hortaea werneckii in the hypersaline waters of salterns, and Cryptococcus liquefaciens in subglacial environments, showed similar profiles of plasma-membrane fluidity in response to raised salinity. The same was seen for ubiquitous fungi, which are generally adapted for different types of stress, such as Aureobasidium pullulans and Rhodotorula mucilaginosa. Representatives of both of these groups modulated their plasma-membrane fluidity differently. When salinity exceeded their optimal range, the ubiquitous stress-tolerant species (A. pullulans, Rh. mucilaginosa) showed increased plasma-membrane fluidity, whereas in the dominant extremophiles (H. werneckii, Cr. liquefaciens), it decreased. On the other hand, the plasma membranes of the fungi with a narrow ecological amplitude (Arctic A. pullulans and Rhodosporium diobovatum) showed different responses.

We sought to reduce tumor hypoxia by topical application of a vasodilator, benzyl nicotinate (BN), and investigated its effect on the growth of tumors irradiated at times when tumor pO 2 increased. EPR oximetry was used to follow the changes in the tissue pO 2 of subcutaneous radiation-induced fibrosarcoma (RIF-1) tumors during topical applications of 1.25-8% BN formulations for 5 consecutive days. The RIF-1 tumors were hypoxic with a tissue pO 2 of 4.6-7.0 mmHg. A significant increase in tumor pO 2 occurred 10-30 min after BN application. The formulation with the minimal BN concentration that produced a significant increase in tumor pO 2 was used for the radiation study. The tumors were irradiated (4 Gy × 5) at the time of the maximum increase in pO 2 observed with the 2.5% BN formulation. The tumors with an increase in pO 2 of greaterthan 2 mmHg from the baseline after application of BN on day 1 had a significant growth inhibition compared to the tumors with an increase in pO 2 of less than 2 mmHg. The results indicate that the irradiation of tumors at the time of an increase in pO 2 after the topical application of the 2.5% BN formulation led to a significant growth inhibition. EPR oximetry provided dynamic information on the changes in tumor pO 2 , which could be used to identify responders and non-responders and schedule therapy during the experiments.

This study was focused on the relationship between the plasma-membrane localization of neurokinin-1 receptor (NK1-R) and its endocytic and signaling properties. First, we employed electron paramagnetic resonance (EPR) to study the domain structure of HEK-293 cells and NK1-R microlocalization. EPR spectra and the GHOST condensation routine demonstrated that NK1-R was distributed in a well-ordered domain of HEK-293 cells possibly representing lipid raft/caveolae microdomains, whereas the impairment of caveolae changed the NK1-R plasma-membrane distribution. Internalization and second messenger assays combined with bioluminescence resonance energy transfer were employed subsequently to evaluate the functional importance of the NK1-R microlocalization in lipid raft/caveolae microdomains. The internalization pattern was delineated through the use of dominant-negative mutants (DNM) of caveolin-1 S80E (Cav1 S80E), dynamin-1 K44A (Dyn K44A), and beta-arrestin (beta-arr 319-418) and by means of cell lines that expressed various endogenous levels of beta-arrestins. NK1-R displayed rapid internalization that was substantially reduced by DNMs of dynamin-1 and beta-arrestin and even more profoundly in cells lacking both beta-arrestin1 and beta-arrestin2. These internalization data were highly suggestive of the predominant use of the clathrin-mediated pathway by NK1-R, even though NK1-R tended to reside constitutively in lipid raft/caveolae microdomains. Evidence was also obtained that the proper clustering of the receptor in these microdomains was important for effective agonist-induced NK1-R signaling and for its interaction with beta-arrestin2.