Capacitative calcium entry mechanism in porcine oocytes.

The presence of the capacitative Ca(2+) entry mechanism was investigated in porcine oocytes. In vitro-matured oocytes were treated with thapsigargin in Ca(2+)-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 Ca(2+) entry. A similar divalent cation influx could also be detected with the Mn(2+)-quench technique after inositol 1,4,5-triphosphate-induced Ca(2+) release. In both cases, lanthanum, the Ca(2+) permeable channel inhibitor, completely blocked the influx caused by store depletion. Heterologous expression of Drosophila trp in porcine oocytes enhanced the thapsigargin-induced Ca(2+) 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 Ca(2+) entry mechanism might help in refilling the intracellular stores after the release of Ca(2+) from the stores. Further investigation is needed to determine whether the trp channel serves as the capacitative Ca(2+) entry pathway in porcine oocytes or is simply activated by the endogenous capacitative Ca(2+) entry mechanism and thus contributes to Ca(2+) influx.