Compatible osmolytes modulate the response of porcine endothelial cells to hypertonicity and protect them from apoptosis

Abstract

Porcine pulmonary arterial endothelial cells accumulated myo‐inositol and taurine, as well as betaine, during adaptation to hypertonic stress. The cells grew and maintained their normal morphology during culture in hypertonic (0.5 osmol (kg H2O)−1) medium that contained osmolytes such as betaine, myo‐inositol or taurine at concentrations close to reported physiological values. The cells did not grow well in hypertonic medium depleted of potential compatible osmolytes. After a few days, cell density decreased by about 50 % and many cells rounded up and detached from the plates, their nuclei showing clear apoptotic morphology. The caspase‐3 activity of the cells also increased dramatically under these conditions, but remained negligibly low when betaine and myo‐inositol were added to the medium. Addition of betaine and myo‐inositol to hypertonic medium depleted of compatible osmolytes increased the number of colonies remaining after 12 days of culture; with each solute at 30–100 μmol l−1 the number increased about sixfold. In the absence of compatible osmolytes, increased mRNA levels and corresponding activities of betaine/γ‐aminobutyric acid transporter (BGT1) and sodium/myo‐inositol transporter (SMIT) induced by hypertonicity remained high after 72 h incubation, whereas they were down regulated in the presence of betaine and myo‐inositol. Similarly, the down regulation of the amino acid System A transporter (ATA2) was markedly slowed in the absence of compatible osmolytes. We conclude that these compatible osmolytes at concentrations close to physiological values enable the endothelial cells to adapt to hypertonic stress, protecting them from apoptosis, and also modulate the adaptation process.

Disruption of F-actin stimulates hypertonic activation of the BGT1 transporter in MDCK cells

“…The action of cytochalasin D on the cytoskeleton was established within 1 h and was maintained for up to 24 h. When included in the uptake medium, none of the tested drugs had an acute effect on BGT1 transport under hypertonic conditions, which rules out a possible direct action on the transporter. The response to cytochalasin D appeared to be selective for BGT1 because cytochalasin D did not stimulate the upregulation of Na ϩ -dependent alanine uptake after 5 h. Alanine enters MDCK cells principally via system A (ATA2), which is also upregulated by 5-6 h of hypertonic stress in both epithelial (9) and endothelial cells (1,2). The unchanged alanine transport following cytochalasin D treatment also provides indirect evidence that the drug does not interfere with maintenance of the transmembrane Na ϩ gradient.…”

Hyperosmotic Stress Induces Aquaporin-dependent Cell Shrinkage, Polyphosphate Synthesis, Amino Acid Accumulation, and Global Gene Expression Changes in Trypanosoma cruzi

“…For example, in a cell-free protein synthesis system, both initiation and elongation are inhibited by high concentrations of inorganic ions but not by compatible osmolytes (32). Compatible osmolytes protect the cells from apoptosis and modulate their adaptive responses (33,34).…”

Dose-dependent effect of FHIT-inducible expression in Calu-1 lung cancer cell line

“…Cell apoptosis was assessed both morphologically and in terms of increased caspase-3 activity as described previously (Fumarola et al, 2001;Alfieri et al, 2002).…”