title: Mitochondrial modulation of Ca2+ -induced Ca2+ -release in rat sensory neurons.
abstract: Ca2+ -induced Ca2+ -release (CICR) from ryanodine-sensitive Ca2+ stores provides a mechanism to amplify and propagate a transient increase in intracellular calcium concentration ([Ca2+]i). A subset of rat dorsal root ganglion neurons in culture exhibited regenerative CICR when sensitized by caffeine. [Ca2+]i oscillated in the maintained presence of 5 mM caffeine and 25 mM K+. Here, CICR oscillations were used to study the complex interplay between Ca2+ regulatory mechanisms at the cellular level. Oscillations depended on Ca2+ uptake and release from the endoplasmic reticulum (ER) and Ca2+ influx across the plasma membrane because cyclopiazonic acid, ryanodine, and removal of extracellular Ca2+ terminated oscillations. Increasing caffeine concentration decreased the threshold for action potential-evoked CICR and increased oscillation frequency. Mitochondria regulated CICR by providing ATP and buffering [Ca2+]i. Treatment with the ATP synthase inhibitor, oligomycin B, decreased oscillation frequency. When ATP concentration was held constant by recording in the whole cell patch-clamp configuration, oligomycin no longer affected oscillation frequency. Aerobically derived ATP modulated CICR by regulating the rate of Ca2+ sequestration by the ER Ca2+ pump. Neither CICR threshold nor Ca2+ clearance by the plasma membrane Ca2+ pump were affected by inhibition of aerobic metabolism. Uncoupling electron transport with carbonyl cyanide p-trifluoromethoxy-phenyl-hydrazone or inhibiting mitochondrial Na+/Ca2+ exchange with CGP37157 revealed that mitochondrial buffering of [Ca2+]i slowed oscillation frequency, decreased spike amplitude, and increased spike width. These findings illustrate the interdependence of energy metabolism and Ca2+ signaling that results from the complex interaction between the mitochondrion and the ER in sensory neurons.
authors.affiliation: Department of Pharmacology, University of Minnesota Medical School, Minneapolis, MN, USA.
authors.forename: Joshua G
authors.initials: JG
authors.lastname: Jackson
authors.forename: Stanley A
authors.initials: SA
authors.lastname: Thayer
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology* / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D005727:Ganglia, Spinal / Q000502:physiology; D008928:Mitochondria / Q000502:physiology*; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D002110:Caffeine; D000255:Adenosine Triphosphate; D002118:Calcium