Ca2+-induced Ca2+ release in Aplysia bag cell neurons requires interaction between mitochondrial and endoplasmic reticulum stores.
Intracellular Ca2+ is influenced by both Ca2+ influx and release. We examined intracellular Ca2+ following action potential firing in the bag cell neurons of Aplysia californica. Following brief synaptic input, these neuroendocrine cells undergo an afterdischarge, resulting in elevated Ca2+ and the secretion of neuropeptides to initiate reproduction. Cultured bag cell neurons were injected with the Ca2+ indicator, fura-PE3, and subjected to simultaneous imaging and electrophysiology. Delivery of a 5-Hz, 1-min train of action potentials (mimicking the fast phase of the afterdischarge) produced a Ca2+ rise that markedly outlasted the initial influx, consistent with Ca2+-induced Ca2+ release (CICR). This response was attenuated by about half with ryanodine or depletion of the endoplasmic reticulum (ER) by cyclopiazonic acid. However, depletion of the mitochondria, with carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone, essentially eliminated CICR. Dual depletion of the ER and mitochondria did not reduce CICR further than depletion of the mitochondria alone. Moreover, tetraphenylphosphonium, a blocker of mitochondrial Ca2+ release, largely prevented CICR. The Ca2+ elevation during and subsequent to a stimulus mimicking the full afterdischarge was prominent and enhanced by protein kinase C activation. Traditionally, the ER is seen as the primary Ca2+ source for CICR. However, bag cell neuron CICR represents a departure from this view in that it relies on store interaction, where Ca2+ released from the mitochondria may in turn liberate Ca2+ from the ER. This unique form of CICR may be used by both bag cell neurons, and other neurons, to initiate secretion, activate channels, or induce gene expression.
Geiger
Julia E
JE
Department of Physiology, Queen's University, Kingston, Ontario, Canada.
Magoski
Neil S
NS
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001048:Aplysia; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002478:Cells, Cultured; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D004721:Endoplasmic Reticulum / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016257:Fura-2 / Q000031:analogs & derivatives / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D008928:Mitochondria / Q000502:physiology*; D008954:Models, Biological; D009474:Neurons / Q000187:drug effects* / Q000648:ultrastructure*; D018408:Patch-Clamp Techniques / Q000379:methods; D012433:Ryanodine / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000031:analogs & derivatives / Q000494:pharmacology; D013942:Thymine Nucleotides / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007211:Indoles; D007476:Ionophores; D013942:Thymine Nucleotides; C098106:fura-PE3; D012433:Ryanodine; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; C016658:phorbolol myristate acetate; D013755:Tetradecanoylphorbol Acetate; C024157:thymidine 5'-triphosphate; D002118:Calcium; D016257:Fura-2; C000543:cyclopiazonic acid