ATP has been demonstrated to act as a co-transmitter or neuromodulator in various physiological processes. There is recent evidence that ATP receptors, characterized as P2 purinergic receptors, are expressed in the sensory hair cells of the auditory organ. The aim of the present study was to know whether other cell types of the organ of Corti, the supporting cells, were also sensitive to external ATP. In both types of supporting cells considered in this study, Deiters' cells (DCs) and Hensen's cells (HEs), extracellular ATP at sub-micromolar concentrations evoked a transient increase in [Ca2+]i as monitored with fluorescence microscopy using the calcium probe Indo-1. An apparent Kd of 0.5 and 0.9 microM was determined for DCs and HEs, respectively. Furthermore, we demonstrated that ATP stimulated Ca2+ release from internal stores in DCs, but not in HEs. Dynamic calcium imaging by confocal laser scanning microscopy of ATP induced Ca2+ mobilization demonstrated a calcium wave propagation in the cell body of DCs which originated in the phalangeal processes, suggesting a functional organization of Ca2+ sequestering stores in DCs.