Mechanism of extracellular ATP-stimulated phosphoinositide hydrolysis in rat glioma C6 cells.
In rat glioma C6 cells, extracellular ATP stimulated phosphoinositide (PI) hydrolysis in concentration- and time-dependent manners with a median effective dose value of 60 microM. The maximal response was attained at 300 microM ATP. Of adenine nucleotides, ATP and adenosine 5'-O-(3-thiotriphosphate) were most effective, while adenosine, AMP and beta,gamma-methylene ATP were ineffective. Similar results were obtained in cultured rat astrocytes. The stimulatory effects of ATP and ADP were negated by removal of external Ca++ in C6 cells. ATP at 300 microM induced an elevation of intracellular Ca++ concentration in 1-[2-(5-carboxyoxazol-2-yl)-6-amino-benzofuran-5-oxy]-2-(2'-amino- 5'- methylphenoxy)-ethane-N,N,N',N' acid-loaded C6 cells. This response was not blocked by nifedipine (10 microM) and verapamil (10 microM). A Ca++ ionophore A23187 (10 microM) stimulated PI hydrolysis in C6 cells. The responses to ATP (300 microM) and A23187 (10 microM) were additive. In digitonin-permeabilized C6 cells, Ca++ at the concentration of 100 microM evoked PI hydrolysis, and ATP alone did not affect the Ca++ dependence. GTP gamma S (100 microM) stimulated the PI hydrolysis at a range of 0.1 to 10 microM Ca++, and ATP enhanced the GTP gamma S response in the permeabilized cells. These results suggest that activation of P2-purinergic receptors by ATP causes phospholipase C to be activated by subthreshold concentrations of Ca++ via GTP-binding proteins, resulting in an activation of the enzyme in response to stimulated Ca++ influx.
Kitanaka
J
J
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Osaka University, Japan.
Hashimoto
H
H
Gotoh
M
M
Mayumi
T
T
Baba
A
A
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001253:Astrocytes / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D005910:Glioma / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006868:Hydrolysis; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D014407:Tumor Cells, Cultured
D010716:Phosphatidylinositols; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000001:Calcimycin; D000255:Adenosine Triphosphate; D002118:Calcium