Effects of mevinolin,an inhibitor of cholesterol synthesis,on the morphology and function of differentiating and differentiated rat adrenocortical cells in primary culture

Summary Mevinolin, an inhibitor of cholesterol synthesis, was used to study the effect of endogenous cholesterol synthesis on the morphology and function of differentiating and differentiated fetal rat adrenocortical cells grown in primary culture. Upon adrenocorticotrophic hormone (ACTH) stimulation under conditions in which endogenous cholesterol synthesis was inhibited but exogenous (lipoprotein) cholesterol was available, the cells differentiated normally from glomerulosa-like to fasciculata-like cells; the steroid hormone secretion was maximally induced. Under conditions in which cholesterol synthesis was maximally inhibited by mevinolin and the cells had no access to exogenous cholesterol, the cells did not differentiate into fasciculata-like cells; the ACTH-induced steroid response was highly suppressed under these conditions. The addition of either human low-density lipoprotein (LDL) or high-density lipoprotein (HDL₃) to the culture medium restored the ACTH-induced differentiation and steroid secretion. Thus, in the absence of exogenous cholesterol, endogenous cholesterol synthesis was a prerequisite for differentiation. In cultures grown in the presence of exogenous cholesterol and ACTH with mevinolin-inhibited cholesterol synthesis and high steroid output, an increase in cytoplasmic lipids was evident, suggesting upregulation of LDL and HDL receptors. The results also demonstrated that induction of phenotypic differentiation from glomerulosalike into fasciculata-like cells can proceed in the presence of a cholesterol synthesis inhibitor like mevinolin; this differentiation in the absence of endogenous cholesterol synthesis is accompanied by the appearance of cytoplasmic cholesterol ester droplets, typical of fasciculata cells.     

The long-wavelength limit of plant photosynthesis

It is a common knowledge that the photosynthesis efficiency drops rapidly under the long-wavelength light excitation above 680 nm. We discovered that in sunflower leaves attached to the plant the initial fall is replaced by an unexpected increase at much longer wavelengths, so that a detectable O(2) evolution is remained till 780 nm. The quantum yield of O(2) evolution at the local maximum at 745 nm reaches almost 20% of the yield at 650 nm. We conclude that extreme long-wavelength chlorophylls may be present in the intact photosystem II antenna system, similarly to photosystem I.     

High-pressure tuning of primary photochemistry in bacterial photosynthesis: membrane-bound versus detergent-isolated reaction centers

Photosynthesis Research - While photosynthesis thrives at close to normal pressures and temperatures, it is presently well known that life is similarly commonplace in the hostile environments of...     

Single-Molecule Spectroscopy Unmasks the Lowest Exciton State of the B850 Assembly in LH2 from Rps. acidophila

We have recorded fluorescence-excitation and emission spectra from single LH2 complexes from Rhodopseudomonas (Rps.) acidophila. Both types of spectra show strong temporal spectral fluctuations that can be visualized as spectral diffusion plots. Comparison of the excitation and emission spectra reveals that for most of the complexes the lowest exciton transition is not observable in the excitation spectra due to the cutoff of the detection filter characteristics. However, from the spectral diffusion plots we have the full spectral and temporal information at hand and can select those complexes for which the excitation spectra are complete. Correlating the red most spectral feature of the excitation spectrum with the blue most spectral feature of the emission spectrum allows an unambiguous assignment of the lowest exciton state. Hence, application of fluorescence-excitation and emission spectroscopy on the same individual LH2 complex allows us to decipher spectral subtleties that are usually hidden in traditional ensemble spectroscopy.     

Biphasic effect of ACTH on growth of rat adrenocortical cells in primary culture

Summary The proliferation rate of differentiating fetal rat adrenocortical cells was studied in primary culture. In this system, stimulation with ACTH induces differentiation of zona glomerulosa-like cortical cells into zona fasciculata-like cells. Incorporation of bromodeoxyuridine (BrdU) was studied immunocytochemically by use of anti-BrdU antibody, and the proliferation rate was counted from the monolayer colonies of adrenocortical cells. After 21 days of cultivation in the absence of ACTH, the proliferation rate of zona glomerulosa-like cells was 10%. The rate slowly declined to 1% at the age of 100 days during continuous cultivation in the absence of ACTH. Stimulation with ACTH induced a strong inhibition in the proliferation rate (down to 2% during the first 24 h). Treatment with ACTH during the following 48 h led to an extremely intense proliferation of adrenocortical cells at a proliferation rate of 25%. Continuous treatment with ACTH up to 100 days led to a persistent growth of adrenocortical cells, and a proliferation rate over 2-fold higher than in control cells cultivated in the absence of ACTH. Thus, ACTH is the principal growth-promoting factor also in vitro, as has been found in in vivo studies. This growth effect is mediated by a biphasic course; at the beginning of differentiation the effect is inhibitory and is followed by a persistent stimulation of the growth of adrenocortical cells.     

Kinetic model of primary energy transfer and trapping in photosynthetic membranes

The picosecond time-domain incoherent singlet excitation transfer and trapping kinetics in core antenna of photosynthetic bacteria are studied in case of low excitation intensities by numerical integration of the appropriate master equation in a wide temperature range of 4-300 K. The essential features of our two-dimensional-lattice model are as follows: Förster excitation transfer theory, spectral heterogeneity of both the light-harvesting antenna and the reaction center, treatment of temperature effects through temperature dependence of spectral bands, inclusion of inner structure of the trap, and transition dipole moment orientation. The fluorescence kinetics is analyzed in terms of distributions of various kinetic components, and the influence of different inhomogeneities (orientational, spectral) is studied.

A reasonably good agreement between theoretical and experimental fluorescence decay kinetics for purple photosynthetic bacterium Rhodospirillum rubrum is achieved at high temperatures by assuming relatively large antenna spectral inhomogeneity: 20 nm at the whole bandwidth of 40 nm. The mean residence time in the antenna lattice site (it is assumed to be the aggregate of four bacteriochlorophyll a molecules bound to proteins) is estimated to be ~12 ps. At 4 K only qualitative agreement between model and experiment is gained. The failure of quantitative fitting is perhaps due to the lack of knowledge about the real structure of antenna or local heating and cooling effects not taken into account.

     

A study of bovine mastitis, milking procedures and management practices on 25 Estonian dairy herds

Background  

Mastitis prevalence, milking procedures and management practices were investigated in 25 big dairy herds supplying milk to an Estonian dairy company. The aim of the study was to provide information for the company to be used in their new udder health improvement program to be set up after the completion of this study.