Involvement of mitochondrial Na+-Ca2+ exchange in intracellular Ca2+ increase induced by ATP in PC12 cells.
The involvement of mitochondrial Na+-Ca2+ exchange in Ca2+ responses to ATP was examined in rat pheochromocytoma (PC) 12 cells. Intracellular Ca2+ ([Ca2+]i) and Na+ concentrations ([Na+]i) were measured using fura-2 and SBFI, respectively. ATP caused concentration-dependent increases in [Ca2+]i and [Na+]i. High concentrations of ATP elicited a Ca2+ transient followed by a slow recovery of [Ca2+]i (a sustained phase) in 77% of PC12 cells. The sustained phase of Ca2+ response appeared only when the peak Ca2+ transient exceeded 500 nM. FCCP, a protonophore, greatly enhanced Ca2+ responses to ATP only in cells with the sustained phase but not without this phase. The sustained phase was decreased by clonazepam and CGP37157, mitochondrial Na+-Ca2+ exchange inhibitors, and extracellular Na+ removal but not by cyclosporin A, an inhibitor of permeability transition pores. The reintroduction of Na+ 3.5 min after ATP stimulation in the absence of Na+ caused Na+ concentration-dependent increases in [Ca2+]i and [Na+]i. The increase in [Na+]i was correlated with that in [Ca2+]i. FCCP caused a great increase in [Ca2+]i 4.5 min after ATP stimulation in the absence of extracellular Na+ but not in its presence, indicating that mitochondria retain Ca2+ in the absence of Na+. These results suggest that ATP causes a large increase in [Ca2+]i which was sequestered in mitochondria and that the sustained phase of Ca2+ response to ATP are mainly due to the release of mitochondrial Ca2+ through Na+-Ca2+ exchangers in PC12 cells.
Maruyama
Kouji
K
Laboratory of Pharmacology, Graduate School of Veterinary Medicine, Hokkaido University, Kita 18, Nishi 9, Sapporo 060-0818, Japan.
Ohta
Toshio
T
Ito
Shigeo
S
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism*; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D016716:PC12 Cells; D051381:Rats; D019831:Sodium-Calcium Exchanger / Q000502:physiology*
D002121:Calcium Channel Blockers; D019831:Sodium-Calcium Exchanger; D000255:Adenosine Triphosphate; D002118:Calcium