title: Agonist-induced mitochondrial Ca2+ transients in smooth muscle.
abstract: We investigated the role of mitochondria (MT) in calcium signaling in a culture of rat aortic smooth muscle cells. We used targeted aequorin to selectively measure [Ca2+] in this organelle. Our results reveal that smooth muscle cell stimulation with agonists causes a large, transient increase in mitochondrial [Ca2+] ([Ca2+]m). This large transient can be blocked with inhibitors of the sarco-endoplasmic reticulum Ca2+-ATPase, suggesting a close relationship between the sarcoplasmic reticulum (SR) and the mitochondria. FCCP completely abolished the response to agonists, and targeted mitochondrial GFP revealed a vast tubular network of MT in these cells. When added before stimulation with ATP, IP3 inhibitors partially blocked the ATP-induced rise in mitochondrial Ca2+ release. The role of the Na+/Ca2+ exchanger (NCX) was examined by removing extracellular Na+. This procedure prevented the decrease in the [Ca2+]m transient normally seen on removal of extracellular Ca2+. We propose a functional linkage of MT and SR dependent on a narrow junctional space between the two organelles in which Ca2+ diffusion is restricted. Approximately half of the mitochondria appear to be associated with the superficial SR, which communicates with the extracellular space via NCX.
authors.affiliation: The iCAPTUR4E Center, University of British Columbia, St. Paul's Hospital, Vancouver, BC, Canada.
authors.forename: Tania
authors.initials: T
authors.lastname: Szado
authors.forename: Kuo-Hsing
authors.initials: KH
authors.lastname: Kuo
authors.forename: Katy
authors.initials: K
authors.lastname: Bernard-Helary
authors.forename: Damon
authors.initials: D
authors.lastname: Poburko
authors.forename: Cheng Han
authors.initials: CH
authors.lastname: Lee
authors.forename: Chun
authors.initials: C
authors.lastname: Seow
authors.forename: Urs T
authors.initials: UT
authors.lastname: Ruegg
authors.forename: Cornelis
authors.initials: C
authors.lastname: van Breemen
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000331:Aequorin / Q000235:genetics; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology; D020013:Calcium Signaling; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002460:Cell Line; D002478:Cells, Cultured; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008928:Mitochondria / Q000378:metabolism*; D008954:Models, Biological; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019831:Sodium-Calcium Exchanger / Q000502:physiology; D014475:Uncoupling Agents / Q000494:pharmacology; D014667:Vasopressins / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D019831:Sodium-Calcium Exchanger; D014475:Uncoupling Agents; D014667:Vasopressins; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D000331:Aequorin; D000255:Adenosine Triphosphate; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases