Proceedings of The Physiological Society

University of Cambridge (2008) Proc Physiol Soc 11, PC138

Poster Communications

Role of immunophilin family of protein in calcium homeostasis in human platelets.

P. C. Redondo1, J. A. Pariente1, G. M. Salido1, J. A. Rosado1

1. Physiology, University of Extremadura, Cáceres, Cáceres, Spain.

Immunophilins are a large family of chaperones that binds to the N-terminus domain of protein containing proline residues. Two immunophilins groups have been described depending of their negative regulation by binding cyclosporin A (CsA, called cyclophilins) or FK506 (called immunophilins)(Adams et al.,2005; Kumar et al., 2005). Both types has been describes regulating calcium homeostasis through its bind to channel receptors, like RYR or IP3R, and calcium-dependent phosphatase, calcineurin (Cameron et al.,1995). The aim of this work is to elucidate the possible regulatory role of this family of protein on calcium homeostasis in platelets. Human platelets were isolated of blood drawn from healthy donor according to Declaration of Helsinki, and treated as previously described(Rosado et al., 2000). Incubation of fura-2 loaded platelet with CsA (10 μM) for 5 min. modified the rate of calcium release induced by the physiological agonist thrombin (0.1 U/mL) and the SERCA modulator, thapsigargin (TG, 200 nM). This modification on intracellular calcium homeostasis induced by CsA may be explained by inhibiting SERCA2b activity, while others Ca2+-ATPases, such as PMCA and SERCA3a remain unaltered. Store operated calcium entry (SOCE) evoked by thrombin or TG were significantly enhanced by incubation of platelets with FK506. Moreover treatment with CsA reported contradictory results depending which agent was used to induce SOCE activation. All together these results shown evidences for an important role of immunophilin in the regulation of calcium levels in human platelets.

Where applicable, experiments conform with Society ethical requirements