title: Dihydropyridine receptors and type 1 ryanodine receptors constitute the molecular machinery for voltage-induced Ca2+ release in nerve terminals.
abstract: Ca2+ stores were studied in a preparation of freshly dissociated terminals from hypothalamic magnocellular neurons. Depolarization from a holding level of -80 mV in the absence of extracellular Ca2+ elicited Ca2+ release from intraterminal stores, a ryanodine-sensitive process designated as voltage-induced Ca2+ release (VICaR). The release took one of two forms: an increase in the frequency but not the quantal size of Ca2+ syntillas, which are brief, focal Ca2+ transients, or an increase in global [Ca2+]. The present study provides evidence that the sensors of membrane potential for VICaR are dihydropyridine receptors (DHPRs). First, over the range of -80 to -60 mV, in which there was no detectable voltage-gated inward Ca2+ current, syntilla frequency was increased e-fold per 8.4 mV of depolarization, a value consistent with the voltage sensitivity of DHPR-mediated VICaR in skeletal muscle. Second, VICaR was blocked by the dihydropyridine antagonist nifedipine, which immobilizes the gating charge of DHPRs but not by Cd2+ or FPL 64176 (methyl 2,5 dimethyl-4[2-(phenylmethyl)benzoyl]-1H-pyrrole-3-carboxylate), a non-dihydropyridine agonist specific for L-type Ca2+ channels, having no effect on gating charge movement. At 0 mV, the IC50 for nifedipine blockade of VICaR in the form of syntillas was 214 nM in the absence of extracellular Ca2+. Third, type 1 ryanodine receptors, the type to which DHPRs are coupled in skeletal muscle, were detected immunohistochemically at the plasma membrane of the terminals. VICaR may constitute a new link between neuronal activity, as signaled by depolarization, and a rise in intraterminal Ca2+.
authors.affiliation: Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
authors.forename: Valérie
authors.initials: V
authors.lastname: De Crescenzo
authors.forename: Kevin E
authors.initials: KE
authors.lastname: Fogarty
authors.forename: Ronghua
authors.initials: R
authors.lastname: Zhuge
authors.forename: Richard A
authors.initials: RA
authors.lastname: Tuft
authors.forename: Lawrence M
authors.initials: LM
authors.lastname: Lifshitz
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Carmichael
authors.forename: Karl D
authors.initials: KD
authors.lastname: Bellvé
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Baker
authors.forename: S
authors.initials: S
authors.lastname: Zissimopoulos
authors.forename: F Anthony
authors.initials: FA
authors.lastname: Lai
authors.forename: José R
authors.initials: JR
authors.lastname: Lemos
authors.forename: John V
authors.initials: JV
authors.lastname: Walsh
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D004558:Electric Stimulation; D004594:Electrophysiology; D007031:Hypothalamus / Q000166:cytology / Q000378:metabolism; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D051379:Mice; D009411:Nerve Endings / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000502:physiology*
chemical_list: D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D011758:Pyrroles; D019837:Ryanodine Receptor Calcium Release Channel; C071658:FPL 64176; D009543:Nifedipine; D002118:Calcium