Endothelin-1 improves the impaired filterability of red blood cells through the activation of protein kinase C.

We previously showed that the deformability of human red blood cells (RBCs) is affected by intracellular signaling pathways by examining the effects of Ca2+ influx and the intracellular cAMP level on mechanically-impaired RBC filterability. In the present study, we investigated whether protein kinase C (PKC) participates in the regulation of RBC deformability by affecting membrane properties. The filterability of mechanically-stressed RBCs showed a V-shaped curve depending on the extracellular Ca2+ concentration; the maximum decrease was achieved at 20-40 microM. The PKC activity, as measured in the membrane-rich fraction by an ELISA method using an antibody for the phosphorylated PKC substrate, maximally increased at the extracellular Ca2+ concentration where the filterability showed a marked improvement following the bottom of the V-shaped curve of the impaired filterability. At this Ca2+ concentration, the PKC activator endothelin-1 increased the PKC activity, and a PKC inhibitor (calphostin C) decreased it. Endothelin-1 improved and calphostin C worsened the impaired filterability. A specific type-B endothelin receptor agonist (IRL 1620) also improved the impaired filterability. A Western blot analysis revealed the presence of endothelin receptors in the RBC membrane. These results indicate that PKC improves the impaired filterability and that RBCs are the target of endothelin-1.