Activation of P2Y but not P2X(4) nucleotide receptors causes elevation of [Ca2+]i in mammalian osteoclasts.
Extracellular nucleotides cause elevation of cytosolic free Ca2+ concentration ([Ca2+](i)) in osteoclasts, although the sources of Ca2+ are uncertain. Activation of P2Y receptors causes Ca2+ release from stores, whereas P2X receptors are ligand-gated channels that mediate Ca2+ influx in some cell types. To examine the sources of Ca2+, we studied osteoclasts from rat and rabbit using fura 2 fluorescence and patch clamp. Nucleotide-induced rise of ([Ca2+](i)) persisted on removal of extracellular Ca2+ (Ca), indicating involvement of stores. Inhibition of phospholipase C (PLC) with U-73122 or inhibition of endoplasmic reticulum Ca(2+)-ATPase with cyclopiazonic acid or thapsigargin abolished the rise of ([Ca2+](i)). After store depletion in the absence of Ca, addition of Ca led to a rise of ([Ca2+](i)) consistent with store-operated Ca2+ influx. Store-operated Ca2+ influx was greater at negative potentials and was blocked by La(3+). In patch-clamp studies where PLC was blocked, ATP induced inward current indicating activation of P2X(4) nucleotide receptors, but with no rise of ([Ca2+](i)). We conclude that nucleotide-induced elevation of [Ca(2+)](i) in osteoclasts arises primarily through activation of P2Y nucleotide receptors, leading to release of Ca2+ from intracellular stores.
Weidema
A F
AF
Department of Physiology and Division of Oral Biology, Faculty of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada N6A 5C1.
Dixon
S J
SJ
Sims
S M
SM
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D003600:Cytosol / Q000201:enzymology; D004533:Egtazic Acid / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D005269:Femur / Q000166:cytology; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D008322:Mammals; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D010010:Osteoclasts / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D058848:Receptors, Purinergic P2X4; D058473:Receptors, Purinergic P2Y2; D019284:Thapsigargin / Q000494:pharmacology; D013977:Tibia / Q000166:cytology; D010738:Type C Phospholipases / Q000378:metabolism
D002614:Chelating Agents; D004791:Enzyme Inhibitors; D004963:Estrenes; D007211:Indoles; C548228:P2rx4 protein, rat; C546387:P2ry2 protein, rat; D010726:Phosphodiesterase Inhibitors; D011760:Pyrrolidinones; D018048:Receptors, Purinergic P2; D058848:Receptors, Purinergic P2X4; D058473:Receptors, Purinergic P2Y2; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D004533:Egtazic Acid; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D010738:Type C Phospholipases; D000252:Calcium-Transporting ATPases; D002118:Calcium; C000543:cyclopiazonic acid