title: Mitochondrial Ca2+ uptake is important over low [Ca2+]i range in arterial smooth muscle.
abstract: Mitochondrial Ca(2+) uptake is usually thought to occur only when intracellular Ca(2+) concentration ([Ca(2+)](i)) is high. We investigated whether mitochondrial Ca(2+) removal participates in shaping [Ca(2+)](i) signals in arterial smooth muscle over a low [Ca(2+)](i) range. [Ca(2+)](i) was measured using fura 2-loaded, voltage-clamped cells from rat femoral arteries. Both diazoxide and carbonyl cyanide m-chlorophenylhydrazone (CCCP) depolarized the mitochondria. Diazoxide application increased resting [Ca(2+)](i), suggesting that Ca(2+) is sequestered in mitochondria. Over a low [Ca(2+)](i) range, diazoxide and CCCP slowed Ca(2+) removal rate, determined after a brief depolarization. When [Ca(2+)](i) was measured during sustained depolarization to -30 mV, CCCP application increased [Ca(2+)](i). When Ca(2+) transients were repeatedly evoked by caffeine applications, CCCP application elevated resting [Ca(2+)](i). Caffeine-induced Ca(2+) transients were compared before and after CCCP application using the half decay time, or time required to reduce increase in [Ca(2+)](i) by 50% (t((1/2))). CCCP treatment significantly increased t((1/2)). These results suggest that Ca(2+) removal to mitochondria in arterial smooth muscle cells may be important at a low [Ca(2+)](i).
authors.affiliation: Department of Human Anatomy and Cell Biology, University of Liverpool, United Kingdom. kamishi@liv.ac.uk
authors.forename: Tomoko
authors.initials: T
authors.lastname: Kamishima
authors.forename: John M
authors.initials: JM
authors.lastname: Quayle
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000493:pharmacokinetics; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002469:Cell Separation; D003981:Diazoxide / Q000494:pharmacology; D005263:Femoral Artery / Q000166:cytology*; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism*; D007425:Intracellular Membranes / Q000187:drug effects / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008931:Mitochondria, Muscle / Q000187:drug effects / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D014475:Uncoupling Agents; D002110:Caffeine; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D003981:Diazoxide; D002118:Calcium