Gradients of O2 concentration in hepatocytes.

1. Cytochrome P/450-dependent mixed function oxidations of hexobarbital, phenyramidol, and alprenolol in intact hepatocytes were examined at different steady state oxygen concentrations. Apparent Kmo2 values were determined to be 6.4 +/- 1.7, 3.6 +/- 0.6, and 9.8 +/- 1.2 micronM, respectively. 2. Apparent Kmo2 values for metabolism of hexobarbital and alprenolol by liver microsomes were 4.3 +/- 0.4 and 8.7 +/- 0.7 micronM, similar to the corresponding values for whole cells. Therefore, no detectable gradient of O2 concentration exists between extracellular space and endoplasmic reticulum of hepatocytes at these oxygen concentrations. 3. Steady state concentrations of ATP, ADP, AMP, lactate, and pyruvate at different steady state oxygen concentrations were used as indicators of mitochondrial oxygen dependence in intact hepatocytes. Half-maximal changes occurred at [O2] = 12.6 micronM for cytoplasmic [NAD+]/[NADH] (estimated from [lactate]/[pyruvate]), at 7.0 micronM for [ATP]/[ADP], and at 2.8 micronM for adenylate energy charge. The apparent cellular respiratory Kmo2 was 1.90 +/- 0.18 micronM. 4. Comparison of values for oxygen dependence of mitochondrial functions in isolated hepatocytes with published values for isolated mitochondria suggests that a substantial intracellular oxygen gradient exists between the outer cellular membrane and the mitochondrial inner membrane at po2 values below the critical O2 tensions.     

High concentration of DNA in condensed chromatin.

The lengths of the DNA molecules of eukaryotic genomes are much greater than the dimensions of the metaphase chromosomes in which they are contained during mitosis. From this observation it has been generally assumed that the linear packing ratio of DNA is an adequate measure of the degree of DNA compaction. This review summarizes the evidence suggesting that the local concentration of DNA is more appropriate than the linear packing ratio for the study of chromatin condensation. The DNA concentrations corresponding to most of the models proposed for the 30-40 nm chromatin fiber are not high enough for the construction of metaphase chromosomes. The interdigitated solenoid model has a higher density because of the stacking of nucleosomes in secondary helices and, after further folding into chromatids, it yields a final concentration of DNA that approaches the experimental value found for condensed chromosomes. Since recent results have shown that metaphase chromosomes contain high concentrations of the chromatin packing ions Mg2+ and Ca2+, it is discussed that dynamic rather than rigid models are required to explain the condensation of the extended fibers observed in the absence of these cations. Finally, considering the different lines of evidence demonstrating the stacking of nucleosomes in different chromatin complexes, it is suggested that the face-to-face interactions between nucleosomes may be the driving force for the formation of higher order structures with a high local concentration of DNA.     

An estimate of melanosome concentration in pigment tissues.

Concentration of melanosomes in various tissues has been unknown because of the impracticability of their direct quantification. Using an indirect approach comprising the estimation of melanin both in freeze-dried tissue samples and in isolated melanosomes, we obtained data on the amount of melanosomes in various pigment tissues. The concentrations of melanosomes found in the tissues were relatively high, not only reflecting the dark color of pigment tissues but also explaining their capacity to perform various functions ascribed to the presence of melanin.     

Protein concentration in urine of normal owl monkeys.

The excretion of urinary protein was evaluated in 62 owl monkeys using timed urine collections. The ratio of urine protein to urine creatinine concentrations (Up/c) was determined for each monkey. Linear regression analysis was used to calculate the correlation between that ratio and urine protein (mg/dl) and 24-hour urinary protein loss (mg/kg). The coefficient of determination for Up/c to urine protein and 24-hour urinary protein loss was significant (P less than or equal to 0.0001). Determination of the Up/c in a urine specimen was found to be an acceptable diagnostic technique for detection and quantitative estimation of proteinuria.     

Developmental changes in rat blood choline concentration.

1. Serum choline concentration in the newborn rat is extremely high and declines as the rat matures until adult values are attained at 20 days of age. 2. Rat milk is a rich source of choline, and rat pups denied access to milk had significantly lower serum choline concentrations than did fed littermates. We conclude that dietary intake of choline contributes to the maintenance of high serum choline concentrations in the neonatal rat. 3. In vivo, choline disappears with a half-life of 70 min. It is converted into betaine, phosphocholine and phosphatidylcholine. The rate of phosphocholine formation is identical in 3- and 10-day-old rats (3.3 mumol/h), whereas the rate of betaine formation is slower in younger animals (0.15 mumol/h at 3 days versus 0.69 mumol/h at 10 days). In vitro, choline oxidase activity [choline dehydrogenase (EC 1.1.99.1) and betaine aldehyde dehydrogenase (EC 1.2.1.8)] increased between birth and 40 days of age. The age-related acceleration in choline's conversion into betaine probably tends to diminish unesterified choline concentration in the rat.     

Sodium ion concentration vs. sweat rate relationship in humans.

The purpose of this study was to determine the effect of active heat acclimation on the sweat osmolality and sweat sodium ion concentration vs. sweat rate relationship in humans. Eight healthy male volunteers completed 10 days of exercise in the heat. The mean exercising heart rate and core temperature were significantly decreased (P < 0.05) by 18 beats/min and 0.6 degrees C, respectively, following heat acclimation. Furthermore, sweat osmolality and the sweat sodium ion concentration vs. sweat rate relationships were shifted to the right. Specifically, the slopes of the relationships were not affected by heat acclimation. Rather, heat acclimation significantly reduced the y-intercepts of the sweat osmolality and sweat sodium relationships with sweat rate by 28 mosmol/kgH(2)O and 15 mmol/l, respectively. Thus there was a significantly lower sweat sodium ion concentration for a given sweat rate following heat acclimation. These results suggest that heat acclimation increases the sodium ion reabsorption capacity of the human eccrine sweat gland.     

On-line determination of animal cell concentration.

A new approach for the indirect determination of cell concentration in the case of nonconstant metabolic rates has been developed. The specific glucose-uptake rate was shown to be nonconstant in batch cultures of free suspended and immobilized CHO SSF3 cells. Time-independent models correlating the specific rate to the limiting substrate concentration were established, thus providing a continuous determination of the specific rate through on-line measurement of the limiting substrate. The method could be applied to determine on-line cell concentration in both free suspended and immobilized cell cultures. Results were verified off-line by crystal violet nuclei counting. The predicted cell concentration was in very good agreement with the off-line reference during the whole exponential-growth phase, until the specific glucose-uptake rate tended to zero.