Ryanodine- and thapsigargin-insensitive Ca2+-induced Ca2+ release is primed by lowering external Ca2+ in rabbit autonomic neurons.
Rises in cytosolic Ca2+ induced by a high K+ concentration (30 or 60 mM) (K+-induced Ca2+ transient) were recorded by fluorimetry of Ca2+ indicators in cultured rabbit otic ganglion cells. When external Ca2+ ([Ca2+]o) was reduced to a micromolar (10-40 microM) or nanomolar (<10 nM) level prior to high-K+ treatment, K+-induced Ca2+ transients of considerable amplitude (50% of control) were generated in most cells, although those initiated at normal [Ca2+]o were reduced markedly or abolished by reducing [Ca2+]o during exposure to a high K+ concentration. Lowering [Ca2+]o alone occasionally caused a transient rise in cytosolic Ca2+. K+-induced Ca2+ transients at micromolar [Ca2+]o were repeatedly generated and propagated inwardly at a speed slower than that at normal [Ca2+]o, while those at nanomolar [Ca2+]o occurred only once. K+-induced Ca2+ transients at micromolar [Ca2+]o were not blocked by ryanodine (10 microM), carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP, 5 microM: at 20-22 degrees C but blocked at 31-34 degrees C) or thapsigargin (1-2 microM), but were blocked by Ni2+ (1 mM) or nicardipine (10 microM). Thus, there is a ryanodine-insensitive Ca2+-release mechanism in FCCP- and thapsigargin-insensitive Ca2+ stores in rabbit otic ganglion cells, which is primed by lowering [Ca2+]o and then activated by depolarization-induced Ca2+ entry. This Ca2+-induced Ca2+ release may operate when [Ca2+]o is decreased by intense neuronal activity.
Nohmi
M
M
First Department of Physiology, Nagoya University, School of Medicine, Japan.
Hua
S Y
SY
Liu
C
C
Kuba
K
K
D000818:Animals; D000831:Animals, Newborn; D001341:Autonomic Nervous System / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009529:Nicardipine / Q000494:pharmacology; D009532:Nickel / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D012433:Ryanodine / Q000494:pharmacology*; D019284:Thapsigargin / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D012433:Ryanodine; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D004533:Egtazic Acid; D019284:Thapsigargin; D009532:Nickel; D009529:Nicardipine; D000252:Calcium-Transporting ATPases; D011188:Potassium; D002118:Calcium