CHARACTERIZATION OF P-2Z PURINERGIC RECEPTORS ON PHAGOCYTIC-CELLS OF THE THYMIC RETICULUM IN CULTURE

The thymic microenvironment is under intrinsic and extrinsic control c ircuits by several elements including hormones, neuropeptides, lymphok ines, innervation and cell contact. P-2 purinergic receptors have been described in a number of cells including macrophages, thymocytes, and other cells of the immune-inflammatory system. Here, we use the whole -cell patch-clamp technique and dye permeabilization assays to investi gate the presence of ionic channels and purinergic receptors in one mi croenvironmental thymic component, namely the phagocytic cell of the t hymic reticulum. At holding potentials ranging from -30 to -60 mV, app lications of extracellular ATP in the vicinity of the cell membrane in duce a transient and fast-activating inward current followed in most c ells by an outward current. The whole event lasts 5-20 s. The inward c urrent has a reversal potential close to 0 mV and the outward current can be ascribed to a Ca2+-dependent K+ conductance. Both currents are inhibited by Mg2+, suggesting that the phenomenon is mediated by ATP(4 -). ATP-gamma-S can also induce both inward and outward currents. Expo sure of phagocytic cells of the thymic reticulum to 5 mM ATP for 10 mi n induced permeabilization to lucifer yellow but not to the larger dye s trypan blue and rhodamine-dextran, suggesting a molecular weight cut -off smaller than 900. These observations lead us to conclude that pha gocytic cells of the thymic reticulum express P-2Z purinergic receptor s that can mobilize Ca2+, induce the opening of ionic channels and per meabilize the cell membrane.