Direct imaging of changes in aerosol particle viscosity upon hydration and chemical aging.

Organic aerosol particles (OA) play major roles in atmospheric chemistry, climate, and public health. Aerosol particle viscosity is highly important since it can determine the ability of chemical species such as oxidants, organics or water to diffuse into the particle bulk. Recent measurements indicate that OA may be present in highly viscous states, however, diffusion rates of small molecules such as water are not limited by these high viscosities. Direct observational evidence of kinetic barriers caused by high viscosity and low diffusivity in aerosol particles were not available until recently; and techniques that are able to dynamically quantify and track viscosity changes during atmospherically relevant processes are still unavailable for atmospheric aerosols. Here we report quantitative, real-time, online observations of microscopic viscosity changes in aerosol particles of atmospherically relevant composition, using fluorescence lifetime imaging (FLIM) of viscosity. We show that microviscosity in ozonated oleic acid droplets and secondary organic aerosol (SOA) particles formed by ozonolysis of myrcene increases substantially with decreasing humidity and atmospheric oxidative aging processes. Furthermore, we found unexpected heterogeneities of microviscosity inside individual aerosol particles. The results of this study enhance our understanding of organic aerosol processes on microscopic scales and may have important implications for the modeling of atmospheric aerosol growth, composition and interactions with trace gases and clouds.

The relationship of increased nuclear protein content induced by hyperthermia to killing of HeLa S3 cells.

The role of a heat-induced increase in nuclear protein mass in killing of cells by hyperthermia was investigated jointly by two groups that had previously reported apparently conflicting results. A correlation between the fraction of HeLa S3 cells killed and the protein content of nuclei isolated immediately after heat exposure was found. This correlation held when thermal sensitivity was modified by the sensitizers 0.41 M ethanol and 5 mM procaine or by the protector 0.6 M glycerol. However, when the HeLa cells were made thermotolerant by a priming heat exposure of 15 min at 45 degrees C followed by 5 h at 37 degrees C, the correlation no longer held. At the 10% survival level a 1.27-fold greater nuclear protein content was observed in tolerant cells relative to nontolerant cells. Thus no general correlation between initial heat-induced nuclear protein mass changes and hyperthermic cell killing exists. When heated cells were returned to 37 degrees C, a time-dependent reduction in the protein content was observed in nuclei isolated after incubation for various times at 37 degrees C. This rate of reduction in nuclear protein content was found to be accelerated in the tolerant cells. Heat-induced changes in cell-cycle progression had no significant effects on the data obtained. It is concluded from the total data base that not only the absolute increment in nuclear protein mass must be taken into account but also the duration of the binding expressed in the rate of recovery.(ABSTRACT TRUNCATED AT 250 WORDS)

Nuclear protein following heat shock: protein removal kinetics and cell cycle rearrangements.

Nuclear protein and DNA content of HeLa cells was determined as a function of time following hyperthermia by staining isolated nuclei with two fluorescent dyes: fluorescein isothiocyanate (FITC) for protein content and propidium iodide (PI) for DNA content. Bivariate FITC and PI histograms were obtained by flow cytometry. Univariate flow cytometric analysis was shown to be inadequate for this study, because some of the nuclear protein changes were due to cell cycle redistribution. Posthyperthermia cell kinetics could be divided into two distinct phases: an early phase characterized by the removal of heat-induced excess nuclear proteins with little or no cell progression through the cell cycle; and a late phase characterized by a redistribution of cells in the cell cycle resulting in an accumulation of cells in G2. The duration of these phases was dependent upon the hyperthermia dose. In the early phase, the rate of removal of excess nuclear protein was found to vary with heating time and temperature for time-temperature combinations which resulted in the same amount of excess nuclear protein. In the late phase, the cells blocked in G2 did not reduce their nuclear protein levels back to control values.

Role of RNA and protein synthesis and turnover in the heat-induced increase in nuclear protein.

The proteins which become associated with nuclei during hyperthermic exposure were characterized by labeled amino acid incorporation. Actinomycin-D (Act-D) or cycloheximide (CHM) pretreatment was used to determine whether concurrent RNA or protein synthesis is required for hyperthermia to induce the increase in nuclear protein content. Prior to heat exposure exponentially growing HeLa cells were (i) pulse labeled for 1 h, (ii) labeled for 36 h, or (iii) labeled for 24 h followed by 17 h chase. The nuclear specific activity (CPM/microgram protein) of [3H]lysine-labeled proteins did not change under any of the labeling conditions, whereas that of [3H]leucine-containing proteins increased significantly with (i) but not with (ii) or (iii), while that of [3H]tryptophan-labeled protein increased significantly with (i) and (ii) but not with (iii). Act-D treatment 1 h prior to and during heating did not affect nuclear protein increase, while CHM-treated cells showed generally less nuclear protein content (70% of control at 60 min) but nevertheless significant nuclear protein increase upon heating (60% increase at 60 min from 0 min). These results suggest that those proteins associated with nuclei following heat exposure are nonhistones with a high turnover rate, and the process dose not require the synthesis of RNA or proteins.

Cell-cycle position and nuclear protein content.

To determine the change in nuclear protein content as a function of cell cycle position, isolated HeLa nuclei were stained for protein with fluorescein isothiocyanate (FITC) and for DNA with propidium iodide (PI) and analyzed by flow cytometry (FCM). The resulting FITC versus PI histogram consisted of four definable regions, a G1 region characterized by increasing FITC and relatively constant PI (2C DNA content), an S region characterized by increasing PI with relatively constant FITC, a G2 region characterized by increasing FITC and constant PI (4C DNA content), and a region of G1 FITC staining with near G2 PI staining. The relationship between cell cycle position and these regions of the histogram was confirmed by the two following studies: 1) The distribution of labeled nuclei throughout the histogram was observed after [14C]TdR pulse labeling. 2) Exit of cells from G1 was observed in the histogram after the addition of Colcemid to the HeLa cell cultures. Nuclear protein content did not appear to increase uniformly across the cell cycle (defined by DNA content). Rather, nuclear protein content showed the largest increase during G1. Thus, dual parameter FCM analysis based on nuclear DNA and protein content provides a more complete definition of cell cycle position than DNA content alone.