The possible involvement of protein phosphatase 1 in thrombin-induced Ca2+ influx of human platelets.
Protein phosphatase 1 is considered to be involved in thrombin-induced platelet activation (Murata et al., Biochem Int 26:327-334, 1992). To clarify the mechanism, we examined the effects of protein phosphatase 1 and 2A inhibitors (calyculin A, tautomycin, okadaic acid) on Ca2+ influx. In the presence of 1 mM Ca2+, thrombin- (0.1 U/ml) induced platelet aggregation and ATP release were inhibited by calyculin A, while this inhibitory effect was abolished in the absence of Ca2+ (EGTA 1 mM). Furthermore, thrombin-induced Mn2+ influx but not intracellular Ca2+ mobilization was inhibited by calyculin A in a dose-related manner. Calyculin A also blocked the ongoing Ca2+ influx when added 3 min after thrombin stimulation. Similar inhibitory effects were observed with okadaic acid and tautomycin in the same potency sequence as the reported one for protein phosphatase 1 (calyculin A > tautomycin > okadaic acid). These results suggest that the anti-platelet effects of phosphatase inhibitors are due to the inhibition of Ca2+ influx and that protein phosphatase 1 plays a key role in the regulation of receptor operated Ca2+ channel of human platelets.
Department of Surgery II, Osaka University Medical School, Japan.
K
K
Murata
M
M
Sakon
J
J
Kambayashi
M
M
Yukawa
Y
Y
Yano
K
K
Fujitani
T
T
Kawasaki
E
E
Shiba
T
T
Mori
D000935:Antifungal Agents / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects; D004988:Ethers, Cyclic / Q000494:pharmacology; D006801:Humans; D008345:Manganese / Q000494:pharmacology; D008387:Marine Toxins; D019319:Okadaic Acid; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000502:physiology*; D010974:Platelet Aggregation / Q000187:drug effects*; D054645:Protein Phosphatase 1; D011714:Pyrans; D013141:Spiro Compounds; D013917:Thrombin / Q000494:pharmacology*
D000935:Antifungal Agents; D015220:Calcium Channels; D004988:Ethers, Cyclic; D008387:Marine Toxins; D010080:Oxazoles; D011714:Pyrans; D013141:Spiro Compounds; C053079:tautomycin; D019319:Okadaic Acid; D008345:Manganese; C059041:calyculin A; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D013917:Thrombin; D002118:Calcium