Effect of acute metabolic acidosis on transmembrane electrolyte gradients in individual renal tubule cells

NADPH oxidases and oxidase crosstalk in cardiovascular diseases: novel therapeutic targets

Reactive oxygen species (ROS)-dependent production of ROS underlies sustained oxidative stress, which has been implicated in the pathogenesis of cardiovascular diseases such as hypertension, aortic aneurysm, hypercholesterolaemia, atherosclerosis, diabetic vascular complications, cardiac ischaemia-reperfusion injury, myocardial infarction, heart failure and cardiac arrhythmias. Interactions between different oxidases or oxidase systems have been intensively investigated for their roles in inducing sustained oxidative stress. In this Review, we discuss the latest data on the pathobiology of each oxidase component, the complex crosstalk between different oxidase components and the consequences of this crosstalk in mediating cardiovascular disease processes, focusing on the central role of particular NADPH oxidase (NOX) isoforms that are activated in specific cardiovascular diseases. An improved understanding of these mechanisms might facilitate the development of novel therapeutic agents targeting these oxidase systems and their interactions, which could be effective in the prevention and treatment of cardiovascular disorders.

Intracellular Na concentration and Rb uptake in proximal convoluted tubule cells and abundance of Na/K-ATPase alpha1-subunit in NHE3-/- mice

Proximal solute and fluid absorption is greatly reduced in mice in which the gene encoding the Na/H exchanger isoform 3 has been ablated (NHE3-/-). To obtain information on the intracellular functional consequences of such selective NHE3 deficiency, Na, Cl and K concentrations and cell Rb uptake were measured using electron microprobe analysis after a 30-s infusion of Rb (an index of basolateral Na/K-ATPase activity) in proximal convoluted tubule (PCT) cells of NHE3-/- and wild-type (NHE3+/+) mice. In addition, the relative abundance of the alpha1-subunit of the Na/K-ATPase in the outer cortex was determined by Western blot analysis. PCT cell Na concentration in NHE3-/- mice was slightly but significantly lower than in NHE3+/+ [13.1+/-0.6 ( n=64) vs. 14.9+/-0.6 ( n=62) mmol/kg wet wt.; means +/-SEM]. The lower intracellular Na concentration was associated with significantly reduced Rb uptake rates [9.7+/-0.6 ( n=59) vs. 14.8+/-0.8 ( n=50) mmol/kg wet wt./30 s], but the abundance of the alpha1-subunit of the Na/K-ATPase was not different between NHE3-/- and NHE3+/+ mice. Intracellular Cl concentration was higher (14.2+/-0.4 vs. 12.8+/-0.4 mmol/kg wet wt.) and K concentration unchanged (122.7+/-2.7 vs. 121.6+/-2.5 mmol/kg wet wt.) in PCT cells in NHE3-/- compared with NHE3+/+ mice. These findings suggest that the elimination of apical NHE3 in PCT cells of NHE3-/- mice reduces apical Na entry and, due to lower cell Na concentrations, Na/K-ATPase activity. The observed changes in intracellular Na concentration did not affect the expression of Na/K-ATPase in the renal cortex of NHE3-/- mice. There were no significant changes of cell Na concentration and Rb uptake in distal convoluted tubule, connecting tubule, principal and intercalated cells.

Ammonium chloride metabolic acidosis and the activity of renin-angiotensin-aldosterone system in children

The present study was undertaken to assess the effects of acute metabolic acidosis on the activity of the renin-angiotensin-aldosterone system in 12 children with a mean age of 8.9 years who underwent NH4Cl loading test. Ammonium chloride was given in a dose of 0.15 g/kg per day for 3 consecutive days to evaluate renal acidification. Prior to and following NH4Cl administration blood acid-base parameters, plasma and urine electrolytes, creatinine and aldosterone concentrations as well as plasma renin activity (PRA), urine flow rate and net H+ excretion were measured. Ammonium chloride administration significantly depressed blood pH (P less than 0.05), bicarbonate (P less than 0.01) and base excess (P less than 0.01) and resulted in a slight, but significant elevation of plasma potassium concentration (P less than 0.05). Furthermore, NH4Cl ingestion induced a marked increase in urine flow rate (P less than 0.01) and urinary sodium, potassium and chloride excretion (P less than 0.01). In response to NH4Cl metabolic acidosis, PRA doubled (4.72 +/- 1.18 vs 8.13 +/- 1.02 ng/ml per hour, P less than or equal to 0.05) and there was a nearly four-fold increase in plasma aldosterone level (0.49 +/- 0.12 vs 1.52 +/- 0.24 ng/ml, P less than 0.01) and in urinary aldosterone excretion (19.2 +/- 4.3 vs 71.8 +/- 13.8 micrograms/day, P less than 0.01). The elevated aldosterone production observed in this study is assumed to be mediated by the combined effect of sodium and water diuresis-related increased PRA, hyperkalaemia and the direct stimulation of adrenal steroidogenesis by metabolic acidosis.

Effect of ammonium-chloride-induced metabolic acidosis on renal electrolyte handling in human neonates

The present study was undertaken to determine the relative contribution of altered glomerular and tubular functions to the metabolic-acidosis-induced increase of renal electrolyte excretion in healthy preterm and full-term neonates and in older infants. Studies were performed in 10 premature infants (mean birth weight 1618 g, gestational age 30.8 weeks) weekly for 6 consecutive weeks, in 11 full-term neonates (mean birth weight 3085 g, gestational age 38.6 weeks) on the 7th day of life and in 25 older control infants (mean age 6.5 months, body weight 6802 g), before and after NH4Cl loading. Blood acid-base parameters, plasma and urine electrolyte and creatinine concentrations were measured, endogenous creatinine clearance and fractional electrolyte excretion (FE) calculated. It was demonstrated that the significant reduction in blood pH and total CO2 content induced by NH4Cl administration was associated with significant increases in glomerular filtration rate (GFR), urine flow rate, FENa and FECl, in each group studied, irrespective of maturity, postnatal age or pre load values. FEK also tended to increase, but the change reached statistical significance only in older infants and in premature babies during the 1st, 2nd and 5th week of post-natal life. FECa and FEPO4 increased slightly in preterm and full-term newborns and became significant in older infants. Prior to NH4Cl administration, FECa correlated positively with FENa in each group. NH4Cl metabolic acidosis, however, dissociated FECa from FENa in the full-term newborns and older infants but not in the preterm neonates.(ABSTRACT TRUNCATED AT 250 WORDS)