CaV3.2 T-type channels mediate Ca2+ entry during oocyte maturation and following fertilization

Abstract

Initiation of mouse embryonic development depends upon a series of fertilization-induced rises in intracellular Ca2+. Complete egg activation requires influx of extracellular Ca2+; however, the channels that mediate this influx remain unknown. Here we tested whether the T-type channel CaV3.2, encoded by Cacna1h, mediates Ca2+ entry into oocytes. We show that mouse eggs express a robust voltage-activated Ca2+ current that is completely absent in Cacna1h−/− eggs. Cacna1h−/− females have reduced litter sizes, and careful analysis of Ca2+ oscillation patterns in Cacna1h−/− eggs following in vitro fertilization (IVF) revealed reductions in first transient length and oscillation persistence. Total and endoplasmic reticulum (ER) Ca2+ stores were also reduced in Cacna1h−/− eggs. Pharmacological inhibition of CaV3.2 in wild type CF-1 strain eggs using mibefradil or pimozide reduced Ca2+ store accumulation during oocyte maturation and reduced Ca2+ oscillation persistence, frequency, and number following IVF. Overall, these data show that CaV3.2 T-type channels have previously unrecognized roles in supporting the meiotic maturation-associated increase in ER Ca2+ stores and mediating Ca2+ influx required for the activation of development.