Calcium influx factor is synthesized by yeast and mammalian cells depleted of organellar calcium stores

Depletion of endoplasmic reticulum Ca(2+) stores leads to the entry of extracellular Ca(2+) into the cytoplasm, a process termed capacitative or store-operated Ca(2+) entry. Partially purified extracts were prepared from the human Jurkat T lymphocyte cell line and yeast in which Ca(2+) stores were depleted by chemical and genetic means, respectively. After microinjection into Xenopus laevis oocytes, the extracts elicited a wave of increased cytoplasmic free Ca(2+) ([Ca(2+)](i)) that spread from the point of injection across the oocyte. Extracts from cells with replete organellar Ca(2+) stores were inactive. The increases depended on extracellular Ca(2+), were unaffected by the inositol 1,4,5-trisphosphate (IP(3)) inhibitor heparin or an anti-IP(3) receptor antibody and were unchanged when the endoplasmic reticulum was segregated to the hemisphere opposite the injection site by centrifugation. Confocal microscopy revealed that [Ca(2+)](i) increases were most pronounced at the periphery of the oocyte. The patterns of [Ca(2+)](i) increases were replicated by computer simulations based on a diffusible messenger of about 700 Da that directly activates Ca(2+) influx. In addition, I(CRAC), a Ca(2+) release-activated Ca(2+) current monitored in Jurkat cells by whole-cell patch clamp recordings, was more rapidly activated when active extracts were included in the patch pipette than by the inclusion of a Ca(2+) chelator or IP(3). These data support the existence in yeast and mammalian cells depleted of Ca(2+) stores of a functionally conserved diffusible calcium influx factor that directly activates Ca(2+) influx.