Anaerobic and aerobic chemostat cultures of Saccharomyces cerevisiae were performed at a constant dilution rate of 0.10 h ؊1 . The glucose concentration was kept constant, whereas the nitrogen concentration was gradually decreasing; i.e., the conditions were changed from glucose and energy limitation to nitrogen limitation and energy excess. This experimental setup enabled the glycolytic rate to be separated from the growth rate. There was an extensive uncoupling between anabolic energy requirements and catabolic energy production when the energy source was present in excess both aerobically and anaerobically. To increase the catabolic activity even further, experiments were carried out in the presence of 5 mM acetic acid or benzoic acid. However, there was almost no effect with acetate addition, whereas both respiratory (aerobically) and fermentative activities were elevated in the presence of benzoic acid. There was a strong negative correlation between glycolytic flux and intracellular ATP content; i.e., the higher the ATP content, the lower the rate of glycolysis. No correlation could be found with the other nucleotides tested (ADP, GTP, and UTP) or with the ATP/ADP ratio. Furthermore, a higher rate of glycolysis was not accompanied by an increasing level of glycolytic enzymes. On the contrary, the glycolytic enzymes decreased with increasing flux. The most pronounced reduction was obtained for HXK2 and ENO1. There was also a correlation between the extent of carbohydrate accumulation and glycolytic flux. A high accumulation was obtained at low glycolytic rates under glucose limitation, whereas nitrogen limitation during conditions of excess carbon and energy resulted in more or less complete depletion of intracellular storage carbohydrates irrespective of anaerobic or aerobic conditions. However, there was one difference in that glycogen dominated anaerobically whereas under aerobic conditions, trehalose was the major carbohydrate accumulated. Possible mechanisms which may explain the strong correlation between glycolytic flux, storage carbohydrate accumulation, and ATP concentrations are discussed.The yeast Saccharomyces cerevisiae is an organism with a remarkable metabolic flexibility. It is one of the few yeasts which are able to grow fermentatively under strictly anaerobic conditions (40). It is also capable of using an entirely respiratory metabolism when sufficient oxygen is available. These two types of catabolism are, however, often used simultaneously. Respiration is the more efficient pathway in terms of ATP production per substrate utilized, but apparently with a limited capacity for high rates compared with fermentation. For instance, by gradually increasing the dilution rate in chemostat cultures, it has been demonstrated that S. cerevisiae uses a strictly respiratory metabolism at low dilution rates whereas at high dilution rates, fermentation is used in addition to respiration (19,29,41).The rates of energy production in these catabolic pathways are not always correlated with the anabolic ene...

Neonatal angiotensin-converting enzyme inhibition or angiotensin II type-1 receptor blockade induces irreversible renal histological abnormalities and an impaired urinary concentrating ability in the rat. The aim of the present study was to determine the pathophysiological mechanisms underlying the defect in urine concentration in adult rats treated neonatally with enalapril. Male Wistar rats received daily intraperitoneal injections of enalapril (10 mg kg(-1)) or saline vehicle from 3 to 24 days of age. Assessments of fluid handling and maximal urine osmolality (Uosm(max)), renal function and tubular free water reabsorption (T(c)H2O) under pentobarbital anaesthesia, renal tissue solute concentrations, renal aquaporin-2 (AQP2) expression, and kidney histology, were performed in 12-16-week-old rats. Uosm(max) (1488 +/- 109 vs. 2858 +/- 116 mosm kg(-1), P < 0.05) and maximal T(c)H2O were reduced in enalapril- vs. vehicle-treated rats after administration of 1-desamino-8-D-arginine vasopressin. Neonatally enalapril-treated rats showed marked papillary atrophy, a decrease in medullary tissue solute concentrations, and a reduction in AQP2 expression specifically in the inner medulla. Glomerular filtration rate, renal plasma flow and urinary excretion rates of sodium, potassium and chloride did not differ between groups. In conclusion, adult rats treated neonatally with enalapril showed a urinary concentrating defect of renal origin which primarily could be explained by the papillary atrophy. However, an impaired ability to generate medullary interstitial hypertonicity, and a decrease in inner medullary AQP2 expression, also seem to contribute to this defect.

Seven different strains of Saccharomyces cerevisiae were tested for the ability to maintain their fermentative capacity during 24 h of carbon or nitrogen starvation. Starvation was imposed by transferring cells, exponentially growing in anaerobic batch cultures, to a defined growth medium lacking either a carbon or a nitrogen source. After 24 h of starvation, fermentative capacity was determined by addition of glucose and measurement of the resulting ethanol production rate. The results showed that 24 h of nitrogen starvation reduced the fermentative capacity by 70 to 95%, depending on the strain. Carbon starvation, on the other hand, provoked an almost complete loss of fermentative capacity in all of the strains tested. The absence of ethanol production following carbon starvation occurred even though the cells possessed a substantial glucose transport capacity. In fact, similar uptake capacities were recorded irrespective of whether the cells had been subjected to carbon or nitrogen starvation. Instead, the loss of fermentative capacity observed in carbon-starved cells was almost surely a result of energy deprivation. Carbon starvation drastically reduced the ATP content of the cells to values well below 0.1 mol/g, while nitrogen-starved cells still contained approximately 6 mol/g after 24 h of treatment. Addition of a small amount of glucose (0.1 g/liter at a cell density of 1.0 g/liter) at the initiation of starvation or use of stationary-phase instead of log-phase cells enabled the cells to preserve their fermentative capacity also during carbon starvation. The prerequisites for successful adaptation to starvation conditions are probably gradual nutrient depletion and access to energy during the adaptation period.

A comparison of catabolic capacity was made between S. cerevisiae cells subjected to 24 h carbon or nitrogen starvation. The cells were shifted to starvation conditions at the onset of respiratory growth on ethanol in aerobic batch cultures, using glucose as the carbon and energy source. The results showed that the catabolic capacity was preserved to a much larger extent during carbon compared to nitrogen starvation. Nitrogen starvation experiments were made in the presence of ethanol (not glucose) to exclude the effect of glucose transport inactivation (Busturia and Lagunas, 1986). Hence, the difference in catabolic capacity could not be attributed to differences in glucose transport capacity during these conditions. In order to understand the reason for this difference in starvation response, measurement of protein composition, adenine nucleotides, inorganic phosphate, polyphosphate and storage carbohydrates were performed. No clear correlation between any of these variables and catabolic capacity after starvation could be obtained. However, there was a positive correlation between total catabolic activity and intracellular ATP concentration when glucose was added to starved cells. The possible mechanism for this correlation, as well as what determines the ATP level, is discussed.

An intact renin-angiotensin system (RAS) during nephrogenesis is essential for normal renal development. We have shown previously that neonatal inhibition of the RAS, either with ANG II type 1-receptor blockade or angiotensin-converting enzyme (ACE) inhibition, induces irreversible renal abnormalities. The aim of the present study was to investigate whether an interrupted RAS can be compensated for by exogenous administration of another important renal growth-promoting factor, the insulin-like growth factor-I (IGF-I). Rats were treated daily with either the ACE inhibitor enalapril (10 mg/kg), recombinant human IGF-I (3 mg/kg), or the combination enalapril + IGF-I from perinatal day 3 to 13. Urinary concentrating ability, renal function, and renal morphology were assessed at adult age. The gene expression and localization of IGF-I, its receptor, and the growth hormone receptor (GHR) were investigated during ongoing ACE inhibition. The present study demonstrates normalized renal function and histology in enalapril + IGF-I-treated animals. Ongoing ACE inhibition suppressed the medullary IGF-I mRNA expression and altered the local distribution of both IGF-I and GHR. Thus the present study provides evidence for an interaction between the RAS and GH/IGF-I axis in renal development.