Rapid agonist-evoked coupling of type II Ins(1,4,5)P3 receptor with XXXX transient receptor potential ( @entity7012 ) channels in @entity1 platelets.

@entity1 @entity8580 @entity3281 @entity7012 @entity593 @entity141
Depletion of intracellular @entity141 stores results in the activation of SMCE (store-mediated @entity141 entry) in many cells. The mechanism of activation of SMCE is poorly understood. In @entity1 platelets, a secretion-like coupling model may be involved. This proposes that store depletion results in trafficking of portions of the endoplasmic reticulum to the plasma membrane, enabling coupling between proteins in the two membranes. In support of this, we have shown that, in @entity1 platelets, agonist-evoked @entity141 store depletion results in de novo and reversible coupling of the Ins P3RII [type II @entity8580 (1,4,5)trisphosphate receptor] with the putative @entity141 entry channel @entity7012 [ @entity1 canonical transient receptor potential 1 (protein); Rosado, Brownlow and Sage (2002) J. Biol. Chem. 277, 42157-42163]. A crucial test of the hypothesis that this coupling activates SMCE is that it should occur rapidly enough to account for agonist-evoked @entity141 entry. In the present study, we have used quenched- and stopped-flow approaches to determine the latencies of thrombin-evoked coupling of Ins P3RII with @entity7012 and of thrombin-evoked bivalent cation entry using @entity3281 quenching of @entity593 fluorescence. Thrombin-evoked @entity3281 entry was detected with a latency of 0.81+/-0.07 s (S.E.M., n =7) or 1.36+/-0.09 s (S.E.M., n =7) at a concentration of 1.0 or 0.1 unit/ml respectively. Coupling between Ins P3RII and @entity7012 , assessed at 100 ms intervals, was first detected with a latency of 0.9 or 1.4 s after stimulation with thrombin at a concentration of 1.0 or 0.1 unit/ml respectively. These results support the hypothesis that de novo coupling of Ins P3RII with @entity7012 could activate SMCE in @entity1 platelets.
