Iono- and metabotropically induced purinergic calcium signalling in rat neocortical neurons

ATP receptor-mediated Ca2+ concentration changes were recorded from neocortical neurones in brain slices from 2 week-old rats. To measure the cytoplasmic concentration of Ca2+ ([Ca2+](i)) slices were incubated with fura-2/AM, and the microfluorimetry system was focused on an individual cell. During transients the intracellular level of [Ca2+](i) in the majority of neocortical neurones (98 of 102) varied in the concentration range of ATP 5-2000 mu M between 41.3 +/- 5 and 163 +/- 7 nM. The rank order of efficacy for purinoreceptor agonists in concentration 100 mu M was: ATP gamma S > ATP > ADP >> AMP approximate to Adenosine approximate to alpha, beta-methylene ATP > UTP. 10 mu M PPADS, a P-2-purinoreceptor antagonist, reduced the ATP-induced [Ca2+](i) response by 26% +/- 4%. After elimination of calcium from extracellular solution the first ATP-induced [Ca2+](i) transient decreased to 65 +/- 8%, suggesting the participation of metabotropic P-2y triggered Ca-release in the generation of the transient. Elevation of cytosolic Ca2+ by activation of plasmalemmal Ca2+ channels failed to potentiate such release indicating the absence of effective reloading of the corresponding stores. No Ca2+-induced Ca2+-release has been observed in the investigated neurons. (C) 1998 Elsevier Science B.V. All rights reserved.