Store-Operated Ca2+ Entry Sustains the Fertilization Ca2+ Signal in Pig Eggs

ABSTRACT The role of store-operated Ca2+ entry (SOCE) in the maintenance of sperm-induced Ca2+ oscillations was investigated in porcine eggs. We found that 10 μM gadolinium (Gd3+), which is known to inhibit SOCE, blocked Ca2+ entry that was triggered by thapsigargin-induced store depletion and also caused an abrupt cessation of the fertilization Ca2+ signal. In a similar manner 3,5-bis(trifluoromethyl)pyrazole 2 (20 μM), and tetrapandin-2 (10 μM), potent SOCE inhibitors, also blocked thapsigargin-stimulated Ca2+ entry and disrupted the Ca2+ oscillations after sperm-egg fusion. The downregulation of Stim1 or Orai1 in the eggs did not alter the Ca2+ content of the intracellular stores, whereas co-overexpression of these proteins led to the generation of irregular Ca2+ transients after fertilization that stopped prematurely. We also found that thapsigargin completely emptied the endoplasmic reticulum, and that the series of Ca2+ transients stopped abruptly after the addition of thapsigargin to the fertilized...