Effects of ATP and derivatives on neuropile glial cells of the leech central nervous system

We investigated the effects of ATP (adenosine 5'-triphosphate) and derivati ves on leech neuropile glial cells, focusing on exposed glial cells. ATP do se-dependently depolarized or hyperpolarized neuropile glial cells in situ as well as exposed neuropile glial cells. These potential shifts varied amo ng cells and repetitive ATP application did not change their amplitude, dur ation or direction. In exposed neuropile glial cells, ATP most frequently i nduced a Na+-dependent depolarization and decreased the input resistance. T he agonist potency ATP > ADP (adenosine 5'-diphosphate) > AMP (adenosine 5' -monophosphate) > adenosine indicates that P2 purinoceptors mediate this de polarization. The P2Y agonist 2-methylthio-ATP mimicked the ATP-induced dep olarization, whereas the P2Y antagonist PPADS (pyridoxal-phosphate-6-azophe nyl-2',4'-disulphonic acid) reduced it. P2X agonists were without effect. B ecause the P1 antagonist 8-SPT (8-(p-sulphophenyl)-theophylline) also depre ssed ATP-induced depolarizations and some ATP-insensitive glial cells respo nded to adenosine, we suggest coexpression of metabotropic P2Y and P1 purin oceptors. The ATP-induced depolarization requires activation of Na+ channel s or nonselective cation channels, whereas the ATP-induced hyperpolarizatio n indicates activation of K+ channels. ATP also increased the intracellular Ca2+ concentration ( [Ca2+](i)), that is independent of Ca2+ influx but re flects intracellular Ca2+ release possibly triggered by IP3 formation. ADP and AMP also increased [Ca2+](i), but were less efficient than ATP; adenosi ne and 2-methylthio-ATP did not affect [Ca2+](i). In view of the mobilizati on of intracellular Ca2+, ATP is clearly different from other leech neurotr ansmitters, because it enables intracellular Ca2+ signaling without causing prominent changes in glial membrane potential. Thus disturbance of the ext racellular microenvironment and the demand for metabolic energy are minimiz ed. (C) 2000 Wiley-Liss, Inc.