5--chloro-5--deoxyadenosine and inositol-1-4-bis(phosphate)

Inositol 1,4-bisphosphate (IP2) which rapidly accumulates during cell activation, strongly stimulates an increase in cytoskeletal actin in saponin-permeated platelets, and the effect is insensitive to 5'-Chloro-5'-deoxyadenosine. Within 10 s, the amount of cytoskeletal actin in platelets rapidly increases by 41%, and then slowly increases further. IP2 induces the increase in cytoskeletal actin in a dose-dependent manner. The half-maximal effect requires approximately 2 microM of IP2. Inositol 1,4,5- triphosphate, the messenger for Ca2+ release, causes the increase in cytoskeletal actin, but is less effective than IP2. Inositol 1-monophosphate and inositol 2-monophosphate have no effect on cytoskeletal actin. Phorbol 12-myristate 13-acetate, which has been shown to activate IP3 5'-phosphatase through protein kinase C, stimulates the increase in cytoskeletal actin. Spermine, an inhibitor of IP3 5'-phosphatase, inhibits the thrombin stimulated increase in cytoskeletal actin. These results suggest that IP2 may be a messenger that controls the organization of actin filaments during cell activation. This study presents the first evidence for IP2 as a messenger during cell activation.

Topics: Actins; Animals; Blood Platelets; Cell Membrane Permeability; Cladribine; Cytoskeleton; Dose-Response Relationship, Drug; Inositol Phosphates; Platelet Activation; Polymers; Saponins; Second Messenger Systems; Spermine; Swine; Tetradecanoylphorbol Acetate; Thrombin

The effects of adenosine and its analogues on the polymerization of actin in pig platelets and the possible mechanism were investigated. The results show that: Thrombin (0.5 U/ml) and ADP (50 mumol/L) stimulate actin polymerization in pig platelets: Adenosine, 5'-chloro-5'-deoxyadenosine, 2'-deoxyadenosine strongly inhibit thrombin- and/or ADP-induced actin polymerization. Adenosine and 5'-chloro-5'-deoxyadenosine strongly inhibit the phosphorylation of phosphatidylinositol in dose-dependent manner, and adenosine reverses the formation of thrombin-stimulated inositol bisphosphate, which has proved to promote the polymerization of actin in saponin-permeated platelets. These suggest that the inhibition of adenosine and its analogues on phosphatidylinositol turnover might involve in their inhibition on actin polymerization in platelets, and phosphatidylinositol turnover might play an important role in actin polymerization during cell activation.

Topics: Actins; Adenosine; Animals; Blood Platelets; Cladribine; Deoxyadenosines; Inositol Phosphates; Phosphatidylinositols; Phosphorylation; Swine