CA2-SENSITIVE INTERNAL STORE - FUNCTIONAL INTERACTIONS BETWEEN MITOCHONDRIA AND THE ER MEASURED IN-SITU IN INTACT-CELLS( HOMEOSTASIS IN THEAGONIST)

Mitochondria have a well-established capacity to detect cytoplasmic Ca 2+ signals resulting from the discharge of ER Ca2+ stores. Conversely, both the buffering of released Ca2+ and ATP production by mitochondri a are predicted to influence ER Ca2+ handling, but this complex exchan ge has been difficult to assess in situ using conventional measurement techniques. Here we have examined this interaction in single intact B HK-21 cells by monitoring intraluminal ER [Ca2+] directly using trappe d fluorescent low-affinity Ca2+ indicators. Treatment with mitochondri al inhibitors (FCCP, antimycin A, oligomycin, and rotenone) dramatical ly prolonged the refilling of stores after release with bradykinin. Th is effect was largely due to inhibition of Ca2+ entry pathways at the plasma membrane, but a significant component appears to arise from red uction of SERCA-mediated Ca2+ uptake, possibly as a consequence of ATP depletions in a localized subcellular domain. The rate of bradykinin- induced Ca2+ release was reduced to 51% of control by FCCP. This effec t was largely overcome by loading cells with BAPTA-AM, highlighting th e importance of mitochondrial Ca2+ buffering in shaping the release ki netics. However, mitochondria-specific ATP production was also a signi ficant determinant of the release dynamic. Our data emphasize the loca lized nature of the interaction between these organelles, and show tha t competent mitochondria are essential for generating explosive Ca2+ s ignals.