Characteristics of the signal transduction system activated by ATP receptors in the hepatoma cell line N1S1-67.
The transmembrane transduction mechanism coupled to purinergic receptors has been studied in a rat hepatoma cell line (N1S1) 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 Ca(2+)-activated K+ channels, leading to membrane hyperpolarization. The order of potency of the various nucleotides tested is UTP = ATP = ADP >> AMP, and ATP > beta, gamma-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 microM ATP. Intracellular injection of (10-20 microM) 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.
Dipartimento di Fisiologia e Biochimica Generali, Università di Milano, Italy.
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Giovannardi
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D008564:Membrane Potentials; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D015398:Signal Transduction
D018048:Receptors, Purinergic P2; C084782:3-deoxy-3-fluoroinositol 1,4,5-trisphosphate; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D002118:Calcium