A CATION NONSELECTIVE CHANNEL INDUCED BY EXTRACELLULAR ATP IN MACROPHAGES AND PHAGOCYTIC-CELLS OF THE THYMIC RETICULUM

Extracellular ATP(4-) can bind to P-2Z purinergic receptors inducing d epolarization and cytoplasmic membrane permeabilization to small molec ular weight solutes in macrophages, thymocytes, mast cells, phagocytic cells of the thymic reticulum and other cell types. An ATP(4-)-induce d cation current has been described in whole-cell records of some of t hese cells but it is currently not clear whether these currents and th e phenomenon of membrane permeabilization are a consequence of only on e type of P-2Z-associated channel/pore or two different phenomena trig gered by one or more receptors. Here we use the outside-out patch-clam p technique to describe a single channel associated with this cation c urrent in two murine phagocytic cells: intraperitoneal macrophages and phagocytic cells of the thymic reticulum. Multi channel currents coul d be readily observed in 77% of the outside-out patches of macrophages . Single channels of 7.8 pS could usually be resolved only in tail cur rents. Reversal potential measurements and ion replacement experiments indicated a lack of cation selectivity, similarly to what has already been described for the ATP(4-)-induced whole-cell inward current. No large-conductance channels that could explain the permeabilization to small molecular weight solutes was observed under our experimental con ditions. A single channel of approx. 5 pS was also observed in phagocy tic cells of the thymic reticulum under similar conditions. We conclud e that the channel here described is the main carrier of cation curren t usually associated with the binding of ATP(4-) to P-2Z receptors in whole-cell and outside-out patch-clamp experiments.