Extracellular ATP increases intracellular calcium in cultured adult Schwann cells

We have previously reported that extracellular ATP causes a transient rise in intracellular calcium concentration ([Ca2+]i) in cultured Schwann cells derived from adult animals [Ansselin A. D. et al. (1994) Int. J. Neurosci. 74, 148]. In this study, the receptor mediating this response has been characterized. Established adult rat and rabbit Schwann cell cultures were loaded with fura-2 (acetoxymethyl ester, 10 micromol/l, 40 min, 37 degrees C). which indicated, by fluorescence imaging, a resting [Ca2+]i of 34.7 +/- 1.4 nmol/l (mean S.E., n=591). The cells were exposed to 100 micromol/l ATP, ADP, AMP, UTP and adenosine in defined medium for 1-2 min, and the change in [Ca2+]i was observed as a change in the Fura-2 ratio. Seventy-seven percent of adult rat Schwann cells (n=235) and 88% adult rabbit Schwann cells (n=356) responded to the presence of extracellular ATP (100 mmol/l) with a transient increase in [Ca2+]i (41 and 90 nmol/l from resting value, respectively), independent of the presence of [Ca2+]o. Calcium waves were observed in one experiment. The following order of agonist potency was observed: UTP= ATP>>ADP>AMP=adenosine. The agonists alpha,beta-methylene-ATP and 2-methylthio-ATP had a small effect on the cells, similar to AMP, and were mutually desensitizing. The ATP antagonist suramin blocked the response. We conclude that adult Schwann cells express a purinergic ATP receptor belonging to the G-protein-coupled P2u alpha subtype [O'Connor S. et al. (1991) Trends pharmac. Sci. 12, 137-141].