The permeability of the human erythrocyte to sodium and potassium

Measurements have been made on the permeability of the human erythrocyte to Na and K in vitro, using radioactive tracers to observe the system in the steady state. The average inward K flux is 1.67 m.eq./liter cells hour, and the apparent activation energy is 12,300 ± 1300 calories/mol. The inward K flux is independent of the external K concentration in the range of concentrations studied (4 to 16 m.eq. K/liter plasma). Rb appears to compete with K for transport into the cell, whereas Na and Li do not. The average inward Na flux is 3.08 ± 0.57 m.eq. Na/liter cells hour, and the apparent activation energies are 20,200 ± 2700 calories/mol for inward transport, and 14,900 ± 3,400 calories/mol for outward transport. The inward Na flux is dependent on the external Na concentration, but not in a linear fashion. Li appears to compete with Na for inward transport, whereas K and Rb do not. An approximate maximum estimate shows that the energy required for cation transport is only 8.8 calories/mol liter cells hour of the 110 calories/mol liter cells hour available from the consumption of glucose. A working hypothesis for the transport of Na and K is presented.     

Adaptive spatiotemporal distribution of soil microfungi in 'Evolution Canyon' II, Lower Nahal Keziv, western Upper Galilee, Israel

We describe and interpret spatiotemporal micromycete community structure and adaptive complexes in contrasting xeric and mesic microclimates in the soils of 'Evolution Canyon' II, Lower Nahal Keziv, western Upper Galilee, Israel. A total of 192 species from 60 genera belonging to Zygomycota (nine species), Ascomycota (13 species), and mitosporic fungi (170 species) were isolated. The fungal communities on the south-facing, xeric, 'African' slope (AS) demonstrated significantly greater diversity than on the north-facing, mesic, 'European' slope (ES) and the valley bottom (VB). Seasonally, winter slope communities were less heterogeneous. Forest localities on the ES and the VB in all seasons and the shady localities on the AS in the winter were overwhelmingly dominated by mesophilic Penicillium species. The sunny locality on the AS was characterized by a dominance of melanin-containing micromycetes that was most pronounced in the summer and by high occurrence and abundance of thermotolerant and thermophilic Aspergillus and Fusarium species. Ascomycetes and zygomycetes were the minor components in all local mycobiota studied; sexual ascomycetes, being stress-selected fungi, were more than ten times more abundant in the soil of the AS than in that of the ES, with the peak of abundance in the sunny summer community. The results demonstrated a microscale adaptive spatiotemporal inter- and intraslope divergence in soil mycobiota structure. Microclimatic natural selection appears to be the major factor affecting soil fungus diversity patterns.  © 2003 The Linnean Society of London . Biological Journal of the Linnean Society , 2003, 78, 527–539.     

Effect of Anionic Salt and Highly Fermentable Carbohydrate Supplementations on Urine pH and on Experimentally Induced Hypocalcaemia in Cows

The objective of this experiment was to determine the effect of dietary grain on calcium homeostasis. Six rumen-fistulated dairy cows with 3 or more previous lactations and no history of parturient paresis were randomly assigned to a sequence of diets in a crossover study with 4 periods of 10 days each. Dietary treatments were: A control ration consisting of wrap grass silage alone (1), the control ration supplemented with ammonium chloride and ammonium sulphate salt solution (2), control ration following a period with supplementation (3) and control ration supplemented with increasing amounts of barley from 4 to 10 kg/cow per day, expected to produce subclinical rumen acidosis (4). Daily intake of the diets was adjusted to 14 kg DM/cow per day. On day 11, the calcium-regulating mechanisms in cows were challenged until recumbency by a standardized intravenous EDTA infusion and cows were left to recover spontaneously. Anion supplementation and the feeding of highly fermentable carbohydrate lowered urine pH below 7.0 due to subclinical acidosis. During spontaneous recovery from EDTA induced hypocalcaemia, the cows more quickly regained a whole blood free calcium concentration of 1.00 mmol/L if they had most recently been supplemented with either anionic salts or with increasing amounts of barley, as compared to the basic ration. It is concluded that so-called slug-feeding or 'steaming up' with highly fermentable carbohydrates before parturition in milk fever susceptible cows enhanced calcium homeostasis similar to the effect seen in cows on anionic diets.     

The effect of ACTH and adrenal steroids on K transport in human erythrocytes

The effect of ACTH and adrenal steroids on K transport in human erythrocytes has been studied. A new method of calculation has revealed that in normal human erythrocytes the K transport is not independent of external K concentration as had previously been thought. The equation describing the relationship is, K influx (m.eq./liter cells hour) = [K]_pi/(0.697 + 0.329 [K]_pi) in which [K]_pi refers to the plasma K concentration at the beginning of the experiment. At the physiological plasma K concentration of 4.65 m.eq./liter, K influx is 2.09 m.eq./liter cells hour; K efflux is 1.95 m.eq./liter cells hour and is independent of plasma K concentration. The effect of the infusion of ACTH and adrenal steroids on the K content of the erythrocytes was also studied. Infusions of ACTH or cortisone do not cause the expected loss in erythrocyte K content and may well cause a gain. Infusions of ACTH and cortisone decrease the rate of K influx and efflux slightly at all stages of the infusion, as measured in vitro in blood samples drawn at various times during and following the infusion. However, the erythrocytes incubated in vitro do not exhibit the same changes in K content as are found in vivo. Hydrocortisone added to normal cells in vitro also decreases both influx and efflux of K, without affecting the K content of the cells.