Intracellular Ca2+ regulation in rat motoneurons during development.
Changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) control the setting up of the neuro-muscular synapse in vitro and probably in vivo. Dissociated cultures of purified embryonic (E15) rat motoneurons were used to explore the molecular mechanisms by which endoplasmic reticulum Ca(2+) stores, via both ryanodine-sensitive and IP(3)-sensitive intracellular Ca(2+) channels control [Ca(2+)](i) homeostasis in these neurons during ontogenesis. Fura-2 microspectrofluorimetry monitorings in single neurons showed that caffeine-induced responses of [Ca(2+)](i) increased progressively from days 1-7 in culture. These responses were blocked by ryanodine and nicardipine but not by omega-conotoxin-GVIA or omega-conotoxin-MVIIC suggesting a close functional relationship between ryanodine-sensitive and L-type Ca(v)1 Ca(2+) channels. Moreover, after 6 days in vitro, neurons exhibited spontaneous or caffeine-induced Ca(2+) oscillations that were attenuated by nicardipine. In 1-day-old neurons, both thapsigargin or CPA, which deplete Ca(2+) stores from the endoplasmic reticulum, induced an increase in [Ca(2+)](i) in 75% of the neurons tested. The number of responding motoneurons declined to 25% at 5-6 days in vitro. Xestospongin-C, a membrane-permeable IP(3) receptor inhibitor blocked the CPA-induced [Ca(2+)](i) response in all stages. RT-PCR studies investigating the expression pattern of RYR and IP(3) Ca(2+) channels isoforms confirmed the presence of their different isoforms and provided evidence for a specific pattern of development for RYR channels during the first week in vitro. Taken together, present results show that the control of motoneuronal [Ca(2+)](i) homeostasis is developmentally regulated and suggest the presence of an intracellular ryanodine-sensitive Ca(2+) channel responsible for a Ca(2+)-induced Ca(2+) release in embryonic motoneurons following voltage-dependent Ca(2+) entry via L-type Ca(2+) channels.
Dayanithi
Govindan
G
INSERM-U 583, Institut des Neurosciences de Montpellier, Hôpital St. Eloi, BP 74103, 80 Rue Augustin FLICHE-34091, Montpellier Cedex 5, France. gdaya@univ-montp2.fr
Mechaly
Ilana
I
Viero
Cédric
C
Aptel
Hervé
H
Alphandery
Sebastien
S
Puech
Sylvie
S
Bancel
Frédéric
F
Valmier
Jean
J
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000096:biosynthesis / Q000502:physiology*; D020746:Calcium Channels, L-Type / Q000502:physiology; D020013:Calcium Signaling / Q000502:physiology*; D005260:Female; D007211:Indoles / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D047028:Macrocyclic Compounds; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D010080:Oxazoles / Q000494:pharmacology; D011247:Pregnancy; D020033:Protein Isoforms / Q000096:biosynthesis; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000096:biosynthesis; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000502:physiology; D013116:Spinal Cord / Q000166:cytology / Q000196:embryology
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D007211:Indoles; D053496:Inositol 1,4,5-Trisphosphate Receptors; D047028:Macrocyclic Compounds; D010080:Oxazoles; D020033:Protein Isoforms; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel; C108644:xestospongin A; D012433:Ryanodine; D002110:Caffeine; D002118:Calcium; C000543:cyclopiazonic acid