PURINOCEPTOR-OPERATED CATIONIC CHANNELS IN HUMAN B-LYMPHOCYTES

1. Using the patch clamp method in the outside-out configuration, puri noceptor-dependent unitary currents were measured in tonsillar and tra nsformed tonsillar human B lymphocytes. 2. Single channel currents wer e evoked by ATP(4-), the free-acid form of ATP, and by 2',3'-O-benzoyl -4-benzoyl-ATP (BzATP) in the micromolar concentration range, but not by 10 mM ADP(3-) or 0.5 mM Mg2+-bound ATP. 3. The channels could be ac tivated and deactivated several times for as long as 30 min even in th e absence of intracellular ATP, GTP, or glucose. 4. The channels were selective for small cations and had a conductance of 9 pS with Cs+ as the intracellular and Na+ as the extracellular monovalent cation.5. Th e half-maximal activation of the channels was obtained by 114 mu M ATP (4-) and by 16 mu M BzATP. The increase in the open probability after raising the ATP(4-) concentration was mainly clue to a decrease in the times the channels spend in the closed state. 6. It is concluded that human B lymphocytes possess cationic channels directly gated by extra cellular ATP(4-). Their agonist binding characteristics are typical fo r P-2Z purinoceptors, but their permeation behaviour is different from the large non-specific pores formed by ATP(4-) in fibroblasts, macrop hages and mast cells.