Dihydropyridine receptors and type 1 ryanodine receptors constitute the molecular machinery for voltage-induced Ca2+ release in nerve terminals.
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+.
De Crescenzo
Valérie
V
Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
Fogarty
Kevin E
KE
Zhuge
Ronghua
R
Tuft
Richard A
RA
Lifshitz
Lawrence M
LM
Carmichael
Jeffrey
J
Bellvé
Karl D
KD
Baker
Stephen P
SP
Zissimopoulos
S
S
Lai
F Anthony
FA
Lemos
José R
JR
Walsh
John V
JV
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*
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