ATP causes release of intracellular Ca2+ via the phospholipase C beta/IP3 pathway in astrocytes from the dorsal spinal cord.
Calcium signaling within astrocytes in the CNS may play a role comparable to that of electrical signaling within neurons. ATP is a molecule known to produce Ca2+ responses in astrocytes, and has been implicated as a mediator of intercellular Ca2+ signaling in other types of nonexcitable cells. We characterized the signal transduction pathway for ATP-evoked Ca2+ responses in cultured astrocytes from the dorsal spinal cord. Nearly 100% of these astrocytes respond to extracellularly applied ATP, which causes release of Ca2+ from an intracellular pool that is sensitive to thapsigargin and insensitive to caffeine. We found that intracellular administration of IP3 also caused release of Ca2+ from a thapsigargin-sensitive intracellular pool, and that IP3 abolished the response to ATP. The ATP-evoked Ca2+ response was blocked by the IP3 receptor antagonist heparin, applied intracellularly, but not by N-desulfated heparin, which is not an antagonist at these receptors. The Ca2+ response caused by ATP was also blocked by a phospholipase C inhibitor, U-73122, but not by its inactive analog, U-73343. Increases in [Ca2+]i were elicited by intracellular application of activators of heterotrimeric G-proteins, GTP gamma S and AIF4-. On the other hand, [Ca2+], was unaffected by a G-protein inhibitor, GDP beta S, but it did abolish the Ca2+ response to ATP. Pretreating the cultures with pertussis toxin did not affect responses to ATP. Our results indicate that in astrocytes ATP-evoked release of intracellular Ca2+ is mediated by IP3 produced as a result of activating phospholipase C coupled to ATP receptors via a G-protein that is insensitive to pertussis toxin. ATP is known to be released under physiological and pathological circumstances, and therefore signaling via the PLC-IP3 pathway in astrocytes is a potentially important mechanism by which ATP may play a role in CNS function.
Salter
M W
MW
Hospital for Sick Children, Department of Physiology, University of Toronto, Ontario, Canada.
Hicks
J L
JL
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D017607:Aluminum Compounds / Q000494:pharmacology; D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers; D015220:Calcium Channels / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D004533:Egtazic Acid / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D005333:Fetus; D005459:Fluorides / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007527:Isoenzymes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011760:Pyrrolidinones / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology*; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D013873:Thionucleotides / Q000494:pharmacology; D013997:Time Factors; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D017607:Aluminum Compounds; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004963:Estrenes; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007527:Isoenzymes; D011760:Pyrrolidinones; D018160:Receptors, Cytoplasmic and Nuclear; D013729:Terpenes; D013873:Thionucleotides; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D006153:Guanosine Diphosphate; C050992:tetrafluoroaluminate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004533:Egtazic Acid; D019284:Thapsigargin; C023427:guanosine 5'-O-(2-thiodiphosphate); D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D006493:Heparin; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D000252:Calcium-Transporting ATPases; D005459:Fluorides; D002118:Calcium