Thrombin-induced phosphodiesteratic cleavage of phosphatidylinositol bisphosphate in human platelets.

To test the latter possibility, we examined the possible presence of alterations in labeled IP:3 in platelets at early times after additionof thrombin

B W Agranoff; P Murthy; E B Seguin

2021

Scholarcy highlights

  • Washed, prelabeled platelets demonstrated a nearly 2-fold increase inPhAactivity within 5 s of thrombin addition, and this increased to 10-fold in 2 min.Relatively little change was seen in PhI radioactivity, and therewas only a marginal decrement in labeled PhIP during this period
  • The increase in PhA labeling is consistent with stimulation of a PhI cycle, and supports previous studies which have shown release of diacylglycerolwithin 5 s of thrombin addition as well as a decrease in the chemical amounts of PhI
  • The observed decrease in radioactivity in PhIP2 in this study raises the possibility that some of the diacylglycerol released by the action of thrombin fist arises from the phosphodiesteratic cleavage of PhIP2.Such enzymatic activity, acting on both PhIP and PhIP2 hasbeen described in erythrocytes,and theselective breakdown of the bisphosphate has recently been reported in muscarinic stimulation of the parotid gland .While loss of label from polyphosphoinositides inplatelets might indicatedephosphorylation to lower inositides, it could alternatively be the result of phosphodiesteratic cleavage
  • To test the latter possibility, we examined the possible presence of alterations in labeled IP:3 in platelets at early times after additionof thrombin
  • The appearance of labeled IP2 and IP:, as major labeled phosphates in the aqueous methanol fractiofnwashed preincubated platelets suggests that they are being released and presumably degraded by endogenous phosphomonoesterases even in the absenceof added thrombin

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