Purinoceptor-operated cationic channels in human B lymphocytes

1. Using the patch clamp method in the outside-out configuration, purinoceptor-dependent unitary currents were measured in tonsillar and transformed tonsillar human B lymphocytes. 2. Single channel currents were 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 activated and deactivated several times for as long as 30 min even in the 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. The 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 extracellular ATP(4-). Their agonist binding characteristics are typical for P-2Z purinoceptors, but their permeation behaviour is different from the large non-specific pores formed by ATP(4-) in fibroblasts, macrophages and mast cells.