The effects of sodium and magnesium-ion interactions on chromatin structure and solubility

The effects of sodium and magnesium-ion interactions on chromatin structure and solubility were examined in isolated mouse liver nuclei. To facilitate this study, a simple assay of chromatin structure was developed, based on the absorbances at 260 nm (A260) and 320 nm (A320) of nuclei in test solutions. By subtracting the A320 from the A260, a single "spectral index" was obtained which served as a useful, but not absolute, indicator of chromatin structure. Electron microscopy verified the validity of this approach. The results indicate that either 200 mM NaCl or 0.5 mM MgCl2 were capable of preserving the native 20 to 30 nm chromatin fiber structure. Below 200 mM NaCl, the native fiber progressively uncoiled to the 10 nm unit fiber. The presence of 0.5 mM MgCl2 inhibited this uncoiling. Only divalent cations stabilized condensed chromatin (heterochromatin) within the nucleus. Monovalent and divalent cations interacted with one another at critical concentrations and modified their individual effects on chromatin structure; e.g., 10 to 25 mM NaCl interfered with the action of 0.5 to 1.5 mM MgCl2, causing a complete loss of condensed chromatin. Maximum solubility of micrococcal nuclease-digested chromatin occurred at 10 mM NaCl, which treatment allowed the chromatin to unfold to the 10 nm fiber. However, ionic conditions that disrupted condensed chromatin but maintained the native chromatin fiber morphology still resulted in relatively high yields of soluble chromatin. Minimum solubility occurred under conditions which preserved the structure of condensed chromatin.     

Obesity: new insight into the anthropometric classification of fat distribution shown by computed tomography.

Twenty eight women presenting for routine computed tomography had their waist, hip, and thigh circumferences measured. The ratio of the area of intra-abdominal fat to the area of subcutaneous fat shown in the computed tomogram taken at the umbilical level was calculated and found to correlate highly significantly with the ratio of waist to hip circumference. The correlation between these two ratios remained significant after allowing for the degree of obesity (weight (kg)/height (m)2) and age. In contrast, there was no significant correlation between the ratio of intra-abdominal to subcutaneous fat and degree of obesity. A high ratio of waist to hip circumference has been shown to be associated with a high proportion of intra-abdominal fat. Thus women with a centralised distribution of fat (high waist to hip ratio: "apples") tend to have a greater proportion of their fat in the intra-abdominal depot than do women with a peripheral fat distribution (low waist to hip ratio: "pears"). The metabolic complications of obesity, which are associated with a high ratio of waist to hip circumference, may therefore relate specifically to the amount of intra-abdominal fat.     

Fatal myocarditis in mice fed rancid purified feed

An outbreak of disease characterized by diarrhea, severe myocarditis, and high mortality occurred in a group of 800 male B6C3F1/ Har mice fed powdered purified diets. A total of 292 animals died. No evidence of an infectious agent was found, and the disease was reproduced in healthy mice by feeding the purified diets, suggesting a nutritional deficiency or toxicity. Analysis of the feed revealed adequate levels of vitamin E, reduced levels of thiamine, and elevated levels of lipoperoxide. It was concluded that mortality was due to myocarditis associated with the ingestion of rancid feed.     

Secretogogue-stimulated phosphatidylinositol breakdown in the exocrine pancreas liberates arachidonic acid, stearic acid, and glycerol by sequential actions of phospholipase C and diglyceride lipase

When mouse pancreatic "minilobules" prelabeled with either [14C]arachidonic acid (AA), [14C]stearic acid (SA), or [3H]glycerol were stimulated with the secretogogue, caerulein, there was a 60-70% loss in radioactivity in phosphatidylinositol (PI) at 30 min. This loss was accompanied by the formation of [14C] phosphatidic acid (PA), [14C]diacylglycerol (DG), [14C] triacylglycerol (TG), and free [14C]AA, [14C]SA, and [3H]glycerol. The loss in radioactive PI was the same as the loss in chemically measured PI-phosphorus. Thirty to fifty per cent of the caerulein-induced loss of prelabeled PI could be accounted for as free [14C]AA, [14C]SA, or [3H]glycerol. Increased incorporation of fatty acid or glycerol residues into DG, PA, and TG accounted for the balance of the loss in PI. The specific DG-lipase inhibitor, RHC 80267, markedly inhibited the caerulein-stimulated release of [14C]AA, [14C]SA, and [3H]glycerol and roughly doubled the caerulein-induced increment in [14C]AA-, [14C]SA-, or [3H]glycerol-labeled DG, showing that the source of the caerulein-induced increment in fatty acids and glycerol was DG. When the PI was prelabeled with either [32P] orthophosphate, [3H]myoinositol, or [3H]glycerol, only 1% or less of the radioactivity in PI was in lysophosphatidylinositol (LPI), and there was no increase in radioactivity in LPI on stimulation with caerulein. These observations, taken together, argue strongly for a phospholipase C-catalyzed breakdown of PI followed by DG-lipase and argue against any significant involvement of phospholipase A2 in PI degradation in mouse pancreas. The formation of substantial amounts of free [14C]AA on stimulation supports the view that, among other things, the phosphoinositide effect in the exocrine pancreas serves to generate arachidonate (and its metabolites). The release of appreciable amounts of free fatty acids and glycerol shows that a significant portion of the DG formed as a result of caerulein-stimulated PI breakdown is not conserved in the phosphoinositide cycle.     

Cavitation Events in Thuja occidentalis L.? : Utrasonic Acoustic Emissions from the Sapwood Can Be Measured

Ultrasonic acoustic emissions (AE) in the frequency range of 0.1 to 1 megahertz appear to originate in the sapwood of Thuja occidentalis L. The AE are vibrations of an impulsive nature. The vibrations can be transduced to a voltage waveform and amplified. The vibrations of each AE event begin at a large amplitude which decays over 20 to 100 microseconds. Strong circumstantial evidence indicates that the ultrasonic AE result from cavitation events because: (a) they occur only when the xylem pressure potential Ψ_xp is more negative than a threshold level of about —1 megapascal; (b) the rate of AE events increases as Ψ_xp decreases and when the net rate of water loss increases; (c) the AE can be stopped by raising Ψ_xp above —1 megapascal. Ultrasonic AE have been measured in whole terminal shoots allowed to dry in the laboratory, in isolated pieces of sapwood as they dried in the laboratory, and in whole terminal shoots in a pressure bomb when Ψ_xp was decreased by lowering the gas pressure in the pressure bomb.     

The Changing Alaskan Experience—Health Care Services and Cultural Identity

Before Western contact, Alaskan Native populations were self-sufficient in their health practices. Slowly, the Native health care system was replaced by a Western one which was highly effective in treating infectious diseases. As infectious diseases were brought under control by the Indian Health Service, the emergent leading health problems were related to violence, attributed in part to cultural disintegration. New types of Native health providers and new Native-controlled institutions evolved to provide culturally appropriate health and mental health services and to promote a stronger cultural identity.     

Accommodation of pyrimidine dimers during replication of UV-damaged simian virus 40 DNA.

UV irradiation of simian virus 40-infected cells at fluences between 20 and 60 J/m2, which yield one to three pyrimidine dimers per simian virus 40 genome, leads to a fluence-dependent progressive decrease in simian virus 40 DNA replication as assayed by incorporation of [3H]deoxyribosylthymine into viral DNA. We used a variety of biochemical and biophysical techniques to show that this decrease is due to a block in the progression of replicative-intermediate molecules to completed form I molecules, with a concomitant decrease in the entry of molecules into the replicating pool. Despite this UV-induced inhibition of replication, some pyrimidine dimer-containing molecules become fully replicated after UV irradiation. The fraction of completed molecules containing dimers goes up with time such that by 3 h after a UV fluence of 40 J/m2, more than 50% of completed molecules contain pyrimidine dimers. We postulate that the cellular replication machinery can accommodate limited amounts of UV-induced damage and that the progressive decrease in simian virus 40 DNA synthesis after UV irradiation is due to the accumulation in the replication pool of blocked molecules containing levels of damage greater than that which can be tolerated.