Christine T. Murphy

Evidence for the presence and location of annexins in human platelets

In this study the identity of annexins in human platelets has been determined together with their ability to be released by agents which induce platelet degranulation. The presence of proteins cross-reacting to antibodies against annexins I and V was detected in human platelets. However, the study provided evidence that these annexins are not located on the surface of the plasma membrane in a Ca++ dependent manner. Moreover, activation of platelets with several agents which induced platelet degranulation did not cause release of annexins I or V as determined by both immunoblotting and ELISA.

6-Deoxy-6-hydroxymethyl scyllo-inositol 1,2,4-trisphosphate: A potent agonist at the inositol 1,4,5-trisphosphate receptor

Abstract The synthesis of racemic 6-deoxy-6-hydroxymethyl scyllo -inositol 1,2,4-trisphosphate is described. This compound is a highly potent agonist at the platelet d - myo -inositol 1,4,5-trisphosphate receptor, and it binds to the rat cerebellar receptor with an affinity equal to that of the natural ligand. These results suggest that the 5″-hydroxymethyl group of adenophostin A may contribute to its unusual potency.

Myo-inositol 1,4,6-trisphosphorothioate and myo-inositol 1,3,4-trisphosphorothioate: New synthetic Ca2+-mobilising partial agonists at the inositol 1,4,5-trisphosphate receptor

Abstract Syntheses of myo -inositol 1,4,6-trisphosphorothioate and 1,3,4-trisphosphorothioate from myo -inositol are described; these trisphosphorothioates, derived from structure-activity considerations of myo -inositol 1,3,4,6-tetrakisphosphate, are low intrinsic activity partial agonists at the platelet Ins(1,4,5)P 3 receptor.

Comparison of the role of protein kinase C in platelet functional responses induced by three different mechanisms, PAF, ionomycin and arachidonic acid.

The role of protein kinase C (PKC) in modulating platelet activation has been examined in platelets pre-incubated with either the PKC activator 12-O-tetradecanoylphorbol 13-acetate (TPA) or the non-specific protein kinase inhibitor, staurosporine. In order to determine where in the signal transduction pathway PKC is exerting its effect platelets were activated either with a receptor-operated stimulus platelet activating factor (PAF) or by direct elevation of [Ca2+]i (ionomycin) or with arachidonic acid which is converted into thromboxane B2 (TxB2). In PAF-stimulated platelets activation of PKC inhibited both [Ca2+]i elevation and TxB2 generation but had no effect on 5-hydroxytryptamine (5-HT) release whilst staurosporine increased the duration of [Ca2+]i elevation and potentiated TxB2 generation but inhibited 5-HT release. In ionomycin-stimulated platelets modulation of PKC had no effect on [Ca2+]i elevation but in contrast to PAF-stimulated platelets PKC activation caused potentiation of TxB2 generation and 5-HT release whilst inhibition of PKC caused inhibition of TxB2 generation and 5-HT release. Modulation of PKC did not affect arachidonic acid-induced TxB2 generation. These findings suggest that in receptor activated platelets endogenously activated PKC is exerting a negative feedback role, however, when [Ca2+]i elevation is not modified by PKC activation or inhibition (such as in ionomycin stimulated platelets) the relationship between the state of PKC activation and subsequent platelet functional responses corresponds more closely. The findings from this study suggest a different relationship between PKC and TxB2 generation than between PKC and dense granule release in PAF-stimulated platelets.