Voltage Dependent N Type Calcium Channel in Mouse Egg Fertilization

Repetitive changes in the intracellular calcium concentration ([Ca(2+)]i) triggers egg activation, including cortical granule exocytosis, resumption of second meiosis, block to polyspermy, and initiating embryonic development. [Ca(2+)]i oscillations that continue for several hours, are required for the early events of egg activation and possibly connected to further development to the blastocyst stage. The sources of Ca(2+) ion elevation during [Ca(2+)]i oscillations are Ca(2+) release from endoplasmic reticulum through inositol 1,4,5 tri-phosphate receptor and Ca(2+) ion influx through Ca(2+) channel on the plasma membrane. Ca(2+) channels have been characterized into voltage-dependent Ca(2+) channels (VDCCs), ligand-gated Ca(2+) channel, and leak-channel. VDCCs expressed on muscle cell or neuron is specified into L, T, N, P, Q, and R type VDCs by their activation threshold or their sensitivity to peptide toxins isolated from cone snails and spiders. The present study was aimed to investigate the localization pattern of N and P/Q type voltage-dependent calcium channels in mouse eggs and the role in fertilization. [Ca(2+)]i oscillation was observed in a Ca(2+) contained medium with sperm factor or adenophostin A injection but disappeared in Ca(2+) free medium. Ca(2+) influx was decreased by Lat A. N-VDCC specific inhibitor, ω-Conotoxin CVIIA induced abnormal [Ca(2+)]i oscillation profiles in SrCl(2) treatment. N or P/Q type VDC were distributed on the plasma membrane in cortical cluster form, not in the cytoplasm. Ca(2+) influx is essential for [Ca(2+)]i oscillation during mammalian fertilization. This Ca(2+) influx might be controlled through the N or P/Q type VDCCs. Abnormal VDCCs expression of eggs could be tested in fertilization failure or low fertilization eggs in subfertility women.