Diadenosine polyphosphate-induced activation of purinoceptor subtypes increases levels of intracellular Ca²⁺ in human fetal astrocytes

Diadenosine polyphosphates (Ap_nAs) are released from and act on P2-subtype purinoceptors in neural cells. Using single cell fura-2 fluorescence to measure levels of free cytosolic Ca²⁺ ([Ca²⁺]j) we determined the extent to which Ap_nAs activate purinoceptors and increase [Ca²⁺]j in human fetal cultured astrocytes. Diadenosine triphosphate, diadenosine tetraphosphate and diadenosine pentaphosphate significantly increased [Ca²⁺]j. Diadenosine pentaphosphate (Ap5A) pressure injected (100 μM) onto astrocytes increased [Ca²⁺]; in 39 out of 65 astrocytes tested; peak increases ranged from 500 to 2000 nM (mean ±SEM, 820 ±142 nM). Chelation of extracellular Ca²⁺ with 2 mM EGTA completely blocked Ap_nA-induced increases in [Ca²⁺];. Pyridoxal-phosphate-6-azophenel-2',4'disulphonic acid tetrasodium (PPADS, 300 μM), a nonselective P_2X/P_2Y purinoceptor antagonist blocked, by over 50 %, Ap5A-induced increases in [Ca²⁺]j. Thapsigargin (4 μM), a Ca²⁺ ATPase inhibitor that depletes Ca²⁺ stores, blocked, by over 75%, ApsA-induced increases in [Ca²⁺]j. Activation of purinoceptor subtypes by Ap_nAs results in significant increases in [Ca²⁺]j and a significant component of the [Ca²⁺]; is released from intracellular stores in human fetal astrocytes.