Activation of store-operated Ca2+ current in Xenopus oocytes requires SNAP-25 but not a diffusible messenger

Depletion of Ca2+ stores in Xenopos 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.