Activation of P2Y but not P2X4nucleotide receptors causes elevation of [Ca2+]iin 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+]ipersisted on removal of extracellular Ca2+(Ca[Formula: see text]), indicating involvement of stores. Inhibition of phospholipase C (PLC) with U-73122 or inhibition of endoplasmic reticulum Ca2+-ATPase with cyclopiazonic acid or thapsigargin abolished the rise of [Ca2+]i. After store depletion in the absence of Ca[Formula: see text], addition of Ca[Formula: see text] led to a rise of [Ca2+]iconsistent with store-operated Ca2+influx. Store-operated Ca2+influx was greater at negative potentials and was blocked by La3+. In patch-clamp studies where PLC was blocked, ATP induced inward current indicating activation of P2X4nucleotide receptors, but with no rise of [Ca2+]i. We conclude that nucleotide-induced elevation of [Ca2+]iin osteoclasts arises primarily through activation of P2Y nucleotide receptors, leading to release of Ca2+from intracellular stores.