Two different mechanisms for the activation of store-operated Ca²⁺ entry (SOCE) have been described in human platelets regulated by two separate Ca²⁺ stores, the dense tubular system and the acidic stores, which can be selectively depleted by treatment with 10 nM TG or 20 mM TBHQ respectively (Rosado JA et al. J. Biol. Chem. 2004 279:29231-5). Tubulin-microtubules play a key role in platelet shape and cellular secretion. Here we analyze the role of tubulin-microtubules in SOCE.Human platelets from healthy donors were obtained according to the declaration of Helsinki.

Fura-2-loaded platelets suspended in a Ca^2+-free medium (100 mM EGTA) were incubated for 30 min with colchicine (30 mM) or paclitaxel (10 mM) and stimulated with TBHQ or TG. Colchicine reduced TBHQ-evoked SOCE by 13.3 ± 5.6% (mean ± SEM; P<0.05 Student's t test; n=8), but increased TG-evoked SOCE by 15.2 ± 5.4% (P<0.01; n=9). In contrast, paclitaxel increased TBHQ-activated SOCE by 18.5 ± 3.5% (P<0.01; n=6) while it reduced TG-activated SOCE by 19.1 ± 5.6% (P<0.01; n=8). Both agents did not modify Ca²⁺ release or extrusion. Tubulin-microtubule has a dual role on the SOCE in human platelets, by participating on two different pathways, and acting as a physical barrier that could reduces the coupling between IP3RII and TRPC conditions, or favouring it, depending on which type of agonist we employed.

Supported by the Wellcome Trust (064070). Redondo PC was supported by Consejería Infraestructura y Desarrollo Tecnológico-Junta Extremadura (POS05A003).