Acute saline infusion induces extracellular acidification and activation of the Na+/H+ exchanger in man.

The effect of acute expansion of the extracellular fluid volume (ECV) with isotonic (0.9%) saline on the activity of the lymphocyte Na+/H+ antiport (NHE) was studied in a total of 18 healthy volunteers. Saline was infused at a constant rate so that 4 mmol kg-1 b.w. was administered over 2 h. NHE activity was measured by quantifying cytosolic pH (pHi) recovery following acidification of the cells with propionic acid and by pH clamping at various pHi values between 7.2 and 5.8 using nigericin. Both methods demonstrate NHE activation associated with intravenous saline infusion, the kinetic difference being a marked decrease in the Hill coefficient n from 3.28 +/- 0.21 (SEM) to 2.22 +/- 0.11 in the absence of changes in baseline pHi (7.14 +/- 0.02 vs. 7.08 +/- 0.02; P = 0.15), Vmax (42.8 +/- 2.7 vs. 48.1 +/- 2.8 mmol L-1 min-1; P = 0.08) and pK (6.32 +/- 0.04 vs. 6.35 +/- 0.02). NHE activation was associated with significant decreases in serum chloride (P = 0.016), calcium (P = 0.008), total cholesterol (P = 0.008), low-density lipoproteins (P = 0.016) and high-density lipoproteins (P = 0.008). Moreover, saline infusion induced extracellular acidification with a decrease in pH from 7.39 +/- 0.01 to 7.37 +/- 0.01 (P = 0.016), HCO3- from 23.3 +/- 0.43 mmol L-1 to 21.3 +/- 0.25 mmol L-1 (P = 0.008) and base excess from -1.03 +/- 0.38 mmol L-1 to -3.00 +/- 0.31 mmol L-1 (P = 0.008). Our results show for the first time that acute ECV expansion with isotonic saline is followed by an activation of the lymphocyte NHE. The underlying mechanism(s) remain to be investigated. However, the demonstration in our study of marked changes in acid-base balance induced by acute saline points to a possible inter-relationship of antiporter activation and extracellular acidification.

Oocyte maturation in the mummichog (Fundulus heteroclitus): effects of steroids on germinal vesicle breakdown of intact follicles in vitro.

The effects of several steroids on the maturation of follicle-enclosed oocytes of the mummichog Fundulus heteroclitus in vitro were examined. At a relatively high concentration (1.0 microgram/ml), a number of different steroids, including pregnenolone, 17 alpha-hydroxypregnenolone, corticosterone, cortisol, 11-deoxycorticosterone, 11-deoxycortisol, androstenedione, testosterone, progesterone, 17 alpha-hydroxyprogesterone, 20 beta-dihydroprogesterone, and 17 alpha-hydroxy-20 beta-dihydroprogesterone, were able to induce germinal vesicle breakdown (GVBD) in prematuration oocytes. Cholesterol, 17 beta-estradiol, 11-ketotestosterone, and 11 beta-hydroxytestosterone were totally ineffective. In general, 11-oxysteroids tended to be less effective than their 11-deoxysteroid counterparts. Two 20 beta-dihydroprogestins--17 alpha-hydroxy-20 beta-dihydroprogesterone and 20 beta-dihydroprogesterone--were the most potent maturation-inducing steroids, initiating 50% GVBD at 1 ng/ml in follicles obtained from ovaries containing mature or maturing follicles in vivo, or at 2.5-4.0 ng/ml in follicles from ovaries lacking mature or maturing oocytes in vivo. These results are consistent with several previous studies involving salmonids and various other teleosts, and suggest a possible physiological role for a 20 beta-dihydroprogestin in the resumption of meiotic maturation in F. heteroclitus.

Freeze-fracture studies of human blood platelets activated by thrombin using rapid freezing.

In this study the influence of thrombin activation on human blood platelets has been followed by freeze-fracturing electron microscopy using rapid freezing in order to catch the initial changes in shape and the morphological alterations during the process of exocytosis of secretory granules. We found that isolation of the platelets by itself leads to some degree of shape change, which made it impossible to study the resting discoid platelet by rapid freezing. Activation of the platelets by thrombin induced dilation of the "surface connecting system (SCS)" with formation of large vacuoles as a result of fusion of the secretory granules with SCS. No intermediary fusion stages or structures were observed even using rapid freezing. Volcano-like protrusions and the corresponding complementary pits were seen at the SCS. These structures were interpreted by us as fractures through protoplasmic channels crossing the SCS. These channels originate during the swelling of the SCS as a result of the fusion of secretory granules with the SCS.

Unstructured model for growth of mycelial pellets in submerged cultures.

An unstructured model is presented to describe growth of mycelial pellets in submerged cultures. This model integrates growth kinetics at the scale of the hyphae with the physical mechanisms of mass-transfer processes at the scale of the pellets and the fermentor. The main elements of the model are biomass, substrate, and oxygen balances for the liquid phase and the pellets. The possible occurrence of oxygen limitation in the pellets is introduced in analogy with catalyst theories by means of an effectiveness factor. To simulate the growth of pellets the model is transferred into a computer program. The model is tested by means of fermentation experiments in a bubble column. Results of the growth experiments compare favorably with the outcome of computer simulations.