Sodium pumps in the Malpighian tubule of Rhodnius sp.

Malpighian tubule of Rhodnius sp. express two sodium pumps: the classical ouabain-sensitive (Na+ + K+)ATPase and an ouabain-insensitive, furosemide-sensitive Na+-ATPase. In insects, 5-hydroxitryptamine is a diuretic hormone released during meals. It inhibits the (Na+ + K+)ATPase and Na+ -ATPase activities indicating that these enzymes are involved in fluid secretion. Furthermore, in Rhodnius neglectus, proximal cells of Malpighian tubule exposed to hyperosmotic medium, regulate their volume through a mechanism called regulatory volume increase. This regulatory response involves inhibition of the (Na+ + K+)ATPase activity that could lead to accumulation of active osmotic solute inside the cell, influx of water and return to the normal cell volume. Adenosine, a compound produced in stress conditions, also inhibits the (Na+ + K+)ATPase activity. Taken together these data indicate that (Na+ + K+)ATPase is a target of the regulatory mechanisms of water and ions transport responsible for homeostasis in Rhodnius sp

The Cystic Fibrosis Transmembrane Regulator (CFTR) in the kidney

The cystic fibrosis transmembrane regulator (CFTR) is a Cl- channel. Mutations of this transporter lead to a defect of chloride secretion by epithelial cells causing the Cystic Fibrosis disease (CF). In spite of the high expression of CFTR in the kidney, patients with CF do not show major renal dysfunction, but it is known that both the urinary excretion of drugs and the renal capacity to concentrate and dilute urine is deficient. CFTR mRNA is expressed in all nephron segments and its protein is involved with chloride secretion in the distal tubule, and the principal cells of the cortical (CCD) and medullary (IMCD) collecting ducts. Several studies have demonstrated that CFTR does not only transport Cl- but also secretes ATP and, thus, controls other conductances such as Na+ (ENaC) and K+ (ROMK2) channels, especially in CCD. In the polycystic kidney the secretion of chloride through CFTR contributes to the cyst enlargement. This review is focused on the role of CFTR in the kidney and the implications of extracellular volume regulators, such as hormones, on its function and expression

Entamoeba histolytica : ouabain-insensitive Na+-ATPase activity

6 p. : il.Our aim was to determine the presence of sodium pumps in Entamoeba histolytica. It is shown through the measurement of ouabainsensitive ATPase activity and immunoblotting that E. histolytica does not express (Na++K+)ATPase. On the other hand, we observed a Na+-ATPase with the following characteristics: (1) stimulated by Na+ or K+, but these effects are not addictive; (2) the apparent affinity is similar for Na+ and K+ (K0.5 = 13.3 ± 3.7 and 15.4 ± 3.1 mM, respectively), as well as the Vmax (24.9 ± 1.5 or 27.5 ± 1.6 nmol Pi mg 1 min 1, respectively); (3) insensitive up to 2 mM ouabain; and (4) inhibited by furosemide with an IC50 of 0.12 ± 0.004 mM. Furthermore, this enzyme forms a Na+- or K+-stimulated, furosemide- and hydroxylamine-sensitive ATP-driven acylphosphate phosphorylated intermediate