Two Pathways for Store-mediated Calcium Entry Differentially Dependent on the Actin Cytoskeleton in Human Platelets

Juan A Rosado,José J López,Alan G.S Harper,Matthew T Harper,Pedro C Redondo,José A Pariente,Stewart O Sage,Ginés M Salido

doi:10.1074/jbc.m403509200

Juan A Rosado, José J López + Show 6 more

Open Access

https://doi.org/10.1074/jbc.m403509200

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Abstract

A major pathway for stimulated Ca(2+) entry in non-excitable cells is activated following depletion of intracellular Ca(2+) stores. Secretion-like coupling between elements in the plasma membrane (PM) and Ca(2+) stores has been proposed as the most likely mechanism to activate this store-mediated Ca(2+) entry (SMCE) in several cell types. Here we identify two mechanisms for SMCE in human platelets activated by depletion of two independent Ca(2+) pools, which are differentially modulated by the actin cytoskeleton. Ca(2+) entry induced by depletion of a 2,5-di-(tert-butyl)-1,4-hydroquinone (TBHQ)-sensitive pool is increased by disassembly of the actin cytoskeleton and that induced by a TBHQ-insensitive pool is reduced. Stabilization of the actin cytoskeleton prevented Ca(2+) entry by both mechanisms. We propose that the membrane-associated actin network prevents constitutive Ca(2+) entry via both pathways. Reorganization of the actin cytoskeleton permits the activation of Ca(2+) entry via both mechanisms, but only SMCE activated by the TBHQ-insensitive pool requires new actin polymerization, which may support membrane trafficking toward the PM.

Highlights

SMCE1 is triggered by depletion of the intracellular Ca2ϩ stores [1], the mechanism underlying this process is not fully understood
Reorganization of the actin cytoskeleton permits the activation of Ca2؉ entry via both mechanisms, but only store-mediated Ca2؉ entry (SMCE) activated by the TBHQ-insensitive pool requires new actin polymerization, which may support membrane trafficking toward the plasma membrane (PM)
Treatment of platelets with cytochalasin D (CytD) did not significantly modify Ca2ϩ release induced by TG alone or in combination with Iono, suggesting that Ca2ϩ accumulation is not affected by disruption of the actin cytoskeleton (Fig. 1B; n ϭ 6)

Summary

Introduction

SMCE1 is triggered by depletion of the intracellular Ca2ϩ stores [1], the mechanism underlying this process is not fully understood. We show that SMCE in platelets is the result of the combined effects of depletion of two different Ca2ϩ stores and that these two pathways are differentially modulated by the actin cytoskeleton.

Results

Conclusion