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Abstract: Cultured astroglia express purinergic receptors that initiate phosphoinositide metabolism and calcium mobilization. Experiments were conducted to characterize the purinergic receptor subtype on type 1 astroglia responsible for stimulating these second‐messenger systems. Inositol phosphate (IP) accumulation and calcium mobilization were measured after stimulation with ATP or purinergic receptor subtype‐selective ATP analogues. ATP (10 –5 M ) increased IP accumulation severalfold. Dose–effect assays monitoring astroglial IP accumulation revealed the order of potency that defines the P 2Y receptor: 2‐methylthioadenosine 5′‐triphosphate > ATP > αβ‐methyleneadenosine 5′‐triphosphate > βγ‐methyleneadenosine 5′‐triphosphate. The influence of ATP on intracellular calcium levels in individual type 1 astroglia was examined using the calcium indicator dye, fura‐2. Dose–effect experiments indicated that ATP was equally potent for generating inositol phosphates and increasing cellular calcium. The most prevalent response (87% of total responses) to ATP consisted of a rapid increase in calcium to a peak level that was approximately five times greater than the prestimulation level. This peak was followed by a decline to a plateau level that was significantly above baseline. This plateau phase of the calcium increase was maintained for at least 5 min in the presence of ATP and was dependent on external calcium. Many (23%) astroglia exhibited spontaneous calcium oscillations whose frequency and magnitude increased after the addition of 10 –5 M ATP. Immunocytochemical staining indicated that the responses occurred in glial fibrillary acidic protein positive cells. We conclude that type 1 astroglia express the P 2Y purinergic receptor which regulates IP production and calcium mobilization.
Helen et al. (Wed,) studied this question.