Intracellular calcium responses to ATP in adult human astrocytes. (A) Representative change in intracellular Ca2+ ([Ca2+]i) (response collated from 20 cells) to ATP (applied at 1 mM) in Ca2+-containing physiological saline solution (PSS). The change in [Ca2+]i exhibited a biphasic time course with time components of 18.5 s and 49 s for the fast and slow phases of decay, respectively. The arrow indicates the inflection point between the rapid and prolonged components of the decay phase of response. (B) Typical mobilization of [Ca2+]i (response collated from 9 cells) induced by a lower level of ATP (applied at 100 μM) in standard PSS. A biphasic change in [Ca2+]i was observed (arrow indicated inflection point) with respective rapid and slow component decay times of 17.8 s and 58.7 s. (C) Representative [Ca2+]i mobilization (response collated from 22 cells) to 1 mM ATP applied in Ca2+-free PSS. A single component of decay of response was observed with a time course of 23.2 s. (D) Representative change in [Ca2+]i (response collated from 20 cells) to 1 mM ATP in the presence of gadolinium (Gd3+ at 2 μM pretreatment for 200 s) in standard PSS. A single monophasic time course of decay for [Ca2+]i was observed with a time course of 25.6 s. All cells shown in this figure were obtained and cultured from a single human surgical case.