Diadenosine pentaphosphate increases levels of intracellular calcium in astrocytes by a mechanism involving release from caffeine/ryanodine- and IP3-sensitive stores.
Diadenosine polyphosphates (ApnAs, n = 2 to 6 phosphate groups) activate P2-type cell-surface adenine nucleotide purinoreceptors, increase the influx of calcium into neural cells, and modulate the binding of ryanodine to ryanodine receptor-regulated intracellular calcium release channels. In this study, we tested the hypothesis, using single cell fluorescence techniques and cultured human fetal astrocytes, that p1, P5-di(adenosine-5') pentaphosphate (Ap5A)-induced increases in levels of intracellular calcium ([Ca2+]i) resulted from release of calcium from intracellular pools. Basal [Ca2+]i were 141+/-12 nM and Ap5A increased [Ca2+]i to 980+/-150 nM. The effect of Ap5A on [Ca2+]i was mediated in part through activation of purinoceptors and influx of extracellular calcium because the purinoceptor antagonist pyridoxal-phosphate-6-azophenel-2', 4'-disuphonic acid blocked by 52%, and chelation of extracellular calcium with EGTA prevented, almost completely, Ap5A-induced increases in [Ca2+]i. Implicating calcium release from IP3- and ryanodine-regulated pools of intracellular calcium were findings that Ap5A-induced increases in [Ca2+]i were blocked, at least in part, by thapsigargin, ryanodine, caffeine, and xestospongin, and Ap5A increased by 2-fold the production of IP3. Release of calcium from IP3- and ryanodine-regulated intracellular pools may be an important signaling event in neural cells that are exposed to Ap5A.
Holden
C P
CP
Department of Pharmacology and Therapeutics, University of Manitoba Faculty of Medicine, Winnipeg, Canada.
Haughey
N J
NJ
Dolhun
B
B
Shepel
P N
PN
Nath
A
A
Geiger
J D
JD
D000255:Adenosine Triphosphate / Q000494:pharmacology; D001253:Astrocytes / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D001920:Bradykinin / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D015226:Dinucleoside Phosphates / Q000494:pharmacology*; D005110:Extracellular Space / Q000378:metabolism; D005333:Fetus / Q000166:cytology; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D047028:Macrocyclic Compounds; D010080:Oxazoles / Q000494:pharmacology; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D058469:Receptors, Purinergic P2X; D058472:Receptors, Purinergic P2Y1; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
D000697:Central Nervous System Stimulants; D015226:Dinucleoside Phosphates; D047028:Macrocyclic Compounds; D010080:Oxazoles; C546382:P2RY1 protein, human; D018048:Receptors, Purinergic P2; D058469:Receptors, Purinergic P2X; D058472:Receptors, Purinergic P2Y1; D019837:Ryanodine Receptor Calcium Release Channel; D014662:Vasoconstrictor Agents; C108644:xestospongin A; D012433:Ryanodine; D002110:Caffeine; C012275:P(1),P(5)-di(adenosine-5'-)pentaphosphate; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D001920:Bradykinin; D002118:Calcium