Characteristics of the signal transduction system activated by ATP receptors in the hepatoma cell line NlSl-67

AbstractThe transmembrane transduction mechanism coupled to purinergic receptors has been studied in a rat hepatoma cell line (NlS1) at the single cell level by a combination of microfluorimetric and electrophysiological techniques. ATP in the micromolar range causes release of Ca2+ from internal stores and consequent opening of Ca2+-activated K+ channels, leading to membrane hyperpolarization. The order of potency of the various nucleotides tested is UTP = ATP = ADP ⪢ AMP, and ATP ⪢ β,γ-CH2 ATP, indicating that these receptors belong to the P2U subtype. The Ca2+ rise induced by various amounts of ATP exhibits an all-or-none behaviour already observable at 10 μM ATP. Intracellular injection of (10–20 μM) InsP3 or of its non-metabolizable analogue 3-F-InsP3 through the patch pipette, does not always result in a Ca2+ rise. These results may be interpreted assuming that the InsP3 receptors-Ca2+ release channels involved in the purinergic/pyrimidinergic stimulation are located in a subcellular compartment not easily accessible from the bulk cytosol and that a positive feedback loop occurs in this restricted space