Recovery of deficient cholinergic calcium signaling by adenosine in cultured rat cortical astrocytes

The regulation of the cholinergic calcium signaling in astroglial cells is thought to play a crucial role in the pathogenesis of Alzheimer's disease. We investigated the action of the cell modulator adenosine on acetylcholine (Ach)-mediated intracellular calcium ([Ca2+](i)) transients in cultured rat cortical astrocytes using the Ca2+ imaging technique. The stable adenosine analog 2-chloroadenosine (2CIA) potentiated the [Ca2+](i) rise induced by activation of muscarinic Ach receptors by shifting similar to30-fold the half-effective Ach concentration. This 2CIA effect was maintained upon removal of extracellular Ca2+, indicating that Ach-induced [Ca2+](i), elevation was due mainly to Ca2+ mobilization from intracellular stores. Pharmacological studies demonstrated that the 2CIA action was mediated by A1 receptors. Incubation with pertussis toxin abrogated the 2CIA effect but left unchanged the [Ca2+](i) rise produced by Ach alone. The [Ca2+](i) response elicited by Ach alone was abolished upon blockade of muscarinic receptor subtypes that stimulate phospholipase C, whereas the [Ca2+](i) elevation generated by the combined action of subthreshold Ach and 2CIA was not affected. Collectively, these results suggest that the impaired cholinergic signaling, the cardinal symptom of Alzheimer's disease, can be reinforced at the second messenger level by an alternative intracellular Ca2+ mobilizing path, which can be brought into play by the concomitant activation of A1 purinoceptors and muscarinic receptors negatively coupled to adenylyl cyclase. (C) 2002 Wiley-Liss, Inc.