Spatial and temporal aspects of Ca2+ signaling mediated by P2Y receptors in cultured rat hippocampal astrocytes.
ATP produces a variety of Ca2+ responses in astrocytes. To address the complex spatio-temporal Ca2+ signals, we analyzed the ATP-evoked increase in intracellular Ca2+ concentration ([Ca2+]i) in cultured rat hippocampal astrocytes using fura-2 or fluo-3 based Ca2+ imaging techniques. ATP at less than 10 nM produced elementary Ca2+ release event "puffs" in a manner independent of extracellular Ca2+. Stimulation with higher ATP concentrations (3 or 10 micro M) resulted in global Ca2+ responses such as intercellular Ca2+ wave. These Ca2+ responses were mainly mediated by metabotropic P2Y receptors. ATP acting on both P2Y1 and P2Y2 receptors produced a transient Ca2+ release by inositol 1,4,5-trisphosphate (InsP3). When cells were stimulated with ATP much longer, the transient [Ca2+]i elevation was followed by sustained Ca2+ entry from the extracellular space. This sustained rise in [Ca2+]i was inhibited by Zn2+ (<10 micro M), an inhibitor of capacitative Ca2+ entry (CCE). CCE induced by cyclopiazonic acid or thapsigargin and Ca2+ entry evoked by ATP share the same pharmacological profile in astrocytes. Taken together, the hierarchical Ca2+ responses to ATP were observed in hippocampal astrocytes, i.e., puffs, global Ca2+ release by InsP3, and CCE in response to depletion of InsP3-sensitive Ca2+ stores. It should be noted that these Ca2+ signals and their modulation by Zn2+ could occur in the hippocampus in situ since both ATP and Zn2+ are rich in the hippocampus and could be released by excitatory stimulation.
Koizumi
Schuichi
S
Division of Pharmacology, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya, 158, Tokyo, Japan. skoizumi@nihs.go.jp
Saito
Yoshiro
Y
Nakazawa
Ken
K
Nakajima
Kazuyuki
K
Sawada
Jun Ichi
JI
Kohsaka
Shinichi
S
Illes
Peter
P
Inoue
Kazuhide
K
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001253:Astrocytes / Q000187:drug effects*; D002118:Calcium / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects*; D002413:Cations, Divalent / Q000494:pharmacology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects*; D007211:Indoles / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D018613:Microscopy, Confocal; D009529:Nicardipine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011983:Receptors, Purinergic / Q000187:drug effects*; D014544:Uridine Triphosphate / Q000494:pharmacology
D002121:Calcium Channel Blockers; D002413:Cations, Divalent; D004791:Enzyme Inhibitors; D007211:Indoles; D011983:Receptors, Purinergic; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D009529:Nicardipine; D002118:Calcium; D014544:Uridine Triphosphate; C000543:cyclopiazonic acid