Store-Operated Ca2+ entry (SOCE) is a ubiquitous mechanism of Ca2+ entry involved in many cellular processes. SOCE is triggered by the Ca2+ depletion of the Endoplasmic Reticulum (ER) which initiates the translocation of the ER Ca2+ sensor STIM1 to the plasma membrane (PM) where it aggregates into punctate structures corresponding to cortical ER subdomains (cER). At the PM, STIM1 gates its channel counterpart Orai1 allowing Ca2+ entry and ER refiling. This thesis work aimed at characterized a longer STIM1 splice variant, STIM1L, mainly expressed in skeletal muscle tissue. We demonstrated STIM1L inability to promote cER expansion contrary to STIM1 while mediating efficient SOCE. We confirmed the requirement of the lysine-rich tail of STIM1 to enlarge these PM contact sites. Finally, we studied STIM1L in the skeletal muscle tissue and localized it in the junctional part of the sarcoplasmic reticulum questioning its involvement as PM Orai1 partner in this context.