Activation of Store-Operated Ca2+ Current in Xenopus Oocytes Requires SNAP-25 but Not a Diffusible Messenger

Depletion of Ca2+ stores in Xenopus oocytes activated entry of Ca2+ across the plasma membrane, which was measured as a current I(soc) in subsequently formed cell-attached patches. I(soc) survived excision into inside-out configuration. If cell-attached patches were formed before store depletion, I(soc) was activated outside but not inside the patches. I(soc) was potentiated by microinjection of Clostridium C3 transferase, which inhibits Rho GTPase, whereas I(soc) was inhibited by expression of wild-type or constitutively active Rho. Activation of I(soc) was also inhibited by botulinum neurotoxin A and dominant-negative mutants of SNAP-25 but was unaffected by brefeldin A. These results suggest that oocyte I(soc) is dependent not on aqueous diffusible messengers but on SNAP-25, probably via exocytosis of membrane channels or regulatory molecules.