Pregnancy-specific modulatory role of mitochondria on adenosine 5'-triphosphate-induced cytosolic [Ca2+] signaling in uterine artery endothelial cells

Vascular endothelial cells respond to extracellular ATP by inositol 1,4,5-trisphosphate-mediated Ca2+ release from the endoplasmic reticulum followed by Ca2+ influx and subsequent synthesis of vasodilators. In this study, the contribution of mitochondria in shaping the ATP-induced Ca2+ increase was examined in ovine uterine artery endothelial cells from nonpregnant and pregnant (late gestation) ewes (NP- and P-UAEC, passage 4). The mitochondrial protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) induced a rapid mitochondrial depolarization. CCCP also slowly increased cytosolic Ca2+] (Ca2+]c), which then gradually declined to 10-20 nM above resting level. Pretreatment with CCCP for 30 min significantly inhibited both ATP and thapsigargin-induced Ca2+]c, with inhibition in NP-UAEC more effective than in P-UAEC. Pretreatment of mitochondrial permeability transition pore inhibitor cyclosporine A did not affect CCCP-induced mitochondrial depolarization, but delayed CCCP-induced Ca2+]c for about 12-15 min (we termed this the "window of time"). During the cyclosporine A-delayed window of time of CCCP-induced Ca2+]c, ATP induced a normal Ca2+ response, but after this window of time, ATP-induced Ca2+]c was significantly inhibited. Pretreatment of oligomycin B to prevent intracellular ATP depletion by F0F1-ATPase did not reduce the inhibition of ATP-induced Ca2+]c by CCCP. Ruthenium red, a mitochondrial Ca2+ uptake blocker, did not mimic the inhibition of Ca2+ signaling by CCCP. In conclusion, our data show that mitochondrial Ca2+ depletion after dissipation of mitochondrial membrane potential with CCCP inhibits ATP-induced Ca2+]c, mediated at the level of Ca2+ release from the endoplasmic reticulum. Moreover, our data revealed that P-UAEC is more resistant to the inhibitory effect of CCCP on Ca2+]c than NP-UAEC.