Interstitial cells of Cajal (ICC) are thought to be pacemakers in the gastrointestinal tract, where they drive gastric and intestinal motility1. Similar cells have been identified in erectile tissue, although their role here is unknown2. In the present study we have isolated ICC from the rabbit corpus cavernosum in order to study the effect of exogenous ATP on their membrane currents. Rabbits were killed by lethal injection with pentibarbitone and their penises removed. The tunica albuginea was opened and the corpus cavernosum extracted and cut into 1 mm3 pieces which were stirred in an enzyme mixture, followed by washing in Hanks Ca2+ free saline to release single ICC and smooth muscle cells (SMC). The cells were then plated for study using the perforated patch clamp technique, using Cs+ rich pipette solution. When cells were held at -60 mV, ATP (20 μM) evoked large inward currents when the pipette and bath [Cl-] were symmetrical (135 mM). Under these conditions the ATP responses were reversibly reduced from 1105 ± 325 pA to 377 ± 97 pA by suramin (100 μM, a broad spectrum purinergic receptor antagonist (n=7, p <0.05). The selective P2Y receptor agonist, 2-methylthio ADP (1 μM), mimicked the effect of ATP. However, while the selective P2Y1 receptor antagonist MRS 2500 (100 nM) effectively reduced the responses to 2-methylthio ADP (from 460 ± 212 pA to 110 ± 82 pA, n=5, p < 0.05), it had a variable effect on the ATP responses, reducing them in only 2 out of 5 cells. This suggests that 2-methylthio ADP mediated its effects via P2Y1 receptors, but that ATP may act on more than one receptor subtype. Also, niflumic acid (100 μM), a blocker of both Ca2+-activated Cl- currents and non-selective cation currents reduced the ATP-evoked currents from -536 ± 143 pA to -60 ± 26 pA (n=6, p <0.05). To test whether ATP-evoked currents were mediated by Cl- or non-selective cation channels, the effects of ATP and caffeine (previously shown to evoke a Ca2+-activated Cl- current in these cells) were compared. When cells were held at -60 mV in symmetrical Cl- solutions, as above, both ATP and caffeine evoked inward currents. However, when ECl was adjusted to -40 mV, by reducing intracellular [Cl-], and cells then held at -10 to -20 mV, ATP still evoked an inward current, but the caffeine-evoked current shifted to the outward direction (n=6). When the external [Na+] was reduced from 130 to 13 mM (by replacement with equimolar NMDG) the ATP current also shifted in the outward direction (n=3), whereas the caffeine evoked current was little affected. These data show that ATP can evoke inward currents in ICC from the corpus cavernosum that are likely to mediated by non-selective cation channels.