Dual effects of ATP on phosphatidylinositol breakdown in rat hepatocyte membranes.
The mechanisms whereby adenosine-5'-triphosphate (ATP) regulates the inositol phospholipid-signalling system were studied in rat hepatocytes. Intact hepatocytes respond to extracellular ATP, adenosine-5'-O-(3-thiotriphosphate) (ATP gamma S), ADP and weakly to guanosine-5'-triphosphate (GTP), but not to other purine nucleotides (GDP or AMP). This is consistent with the idea that a P2 purinergic receptor is coupled to the phosphatidylinositol metabolism in these cells. Partially purified plasma membranes prepared from myo-[3H]inositol prelabelled hepatocytes exhibit a phosphatidylinositol-4,5-bisphosphate phospholipase C activity sensitive to ATP, ATP gamma S and guanosine-5'-O-(3-thiotriphosphate) (GTP gamma S). Moreover the GTP gamma S effect is greatly enhanced by ATP and ATP gamma S. These potentiating effects differ according to the adenylnucleotide considered. ATP produces (1) an increase in the GTP gamma S-PLC sensitivity, (2) a potentiation of the phospholipase C (PLC) response induced by maximal dose of GTP gamma S, and (3) an increase in the inositol lipids pools. At variance, ATP gamma S, a nonhydrolysable analogue of ATP, only increases the PLC-sensitivity towards GTP gamma S. These results may signify that ATP stimulates inositol phosphate accumulation via at least two distinct mechanisms (i) a direct activation of a P2 purinergic receptor coupled to a PLC via a GTP binding protein and (ii) a stimulation of the phosphatidylinositol (PI) and phosphatidylinositol-4-phosphate (PIP) kinases which increased the pool of phospholipase C substrates.
Ibarrondo
J
J
Departamento de Bioquimica y Biología Molecular, Facultad de Ciencias, Universidad del Pais Vasco/Euskal Herriko Unibertsitatea, Bilabo, Spain.
Marino
A
A
Guillon
G
G
Trueba
M
M
Macarulla
J M
JM
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology*; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004789:Enzyme Activation; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D010738:Type C Phospholipases / Q000378:metabolism*
D010716:Phosphatidylinositols; C022571:adenosine 5'-O-(3-thiotriphosphate); D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D010738:Type C Phospholipases