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The presence of the capacitative Ca2+ entry mechanism was investigated in porcine oocytes. In vitro-matured oocytes were treated with thapsigargin in Ca2+-free medium for 3 h to deplete intracellular calcium stores. After restoring extracellular calcium, a large calcium influx was measured by using the calcium indicator dye fura-2, indicating capacitative Ca2+ entry. A similar divalent cation influx could also be detected with the Mn2+-quench technique after inositol 1,4,5-triphosphate-induced Ca2+ release. In both cases, lanthanum, the Ca2+ permeable channel inhibitor, completely blocked the influx caused by store depletion. Heterologous expression of Drosophila trp in porcine oocytes enhanced the thapsigargin-induced Ca2+ influx. Polymerase chain reaction cloning using primers that were designed based on mouse and human trp sequences revealed that porcine oocytes contain a trp homologue. As in other cell types, the capacitative Ca2+ entry mechanism might help in refilling the intracellular stores after the release of Ca2+ from the stores. Further investigation is needed to determine whether the trp channel serves as the capacitative Ca2+ entry pathway in porcine oocytes or is simply activated by the endogenous capacitative Ca2+ entry mechanism and thus contributes to Ca2+ influx.

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Biology of Reproduction

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