Depolarization potentiates P2Y1 receptors stimulated by weak, partial and strong, full agonists. (a–c) Agonist- and depolarization-evoked [Ca2+]i responses during application of the weak agonist ATP at a physiologically relevant concentration (1 μM, a) or the strong agonist, 2MeSADP, at either 1 μM (b) or a value close to its reported EC50 (10 nM, c). (d) Average depolarization-evoked [Ca2+]i responses at 1 μM ADP, ATP and 2MeSADP, and 10 nM 2MeSADP.