Effects of pentoxifylline on Ca2+-dependent transglutaminase in rat erythrocytes

We have examined the effects of pentoxifylline, a drug used to improve peripheral blood flow in patients with chronic vascular disorders, on shear-induced Ca2+ entry and Ca2+-dependent protein crosslinking in the erythrocyte. Cells were washed in isosmotic bicarbonate buffer, pH 7.5, and brought to a 20% suspension. 5 ml samples were sheared by swirling them for seconds; 45Ca2+ uptake, activation of Ca2+-dependent transglutaminase, and products of the crosslinking reaction were measured. A 5 second shear promoted 45Ca2+ entry, activation of Ca2+-dependent transglutaminase and crosslinking of proteins in the membrane-cytoskeletal fraction. Pentoxifylline, a drug that promotes erythrocyte deformability, diminished Ca2+ entry and inhibited activation of Ca2+-dependent transglutaminase, and had a prophylactic role on the effects of Ca2+ entry due to shear. Incubation of cells with 2.5 mM pentoxifylline before swirling minimized the effects of shear on 45Ca2+ entry, Ca2+-dependent transglutaminase and crosslinking of proteins. This study indicates that pentoxifylline promotes erythrocyte flexibility by minimizing shear-induced Ca2+ entry and Ca2+-dependent crosslinking.