Stimulation and inhibition of human platelet membrane high‐affinity GTPase by neomycin

Abstract

The effect of the inositol phospholipid-binding antibiotic neomycin was studied on high-affinity GTPase in human platelet membranes. At low concentrations (up to 1 mM), neomycin by itself stimulated a high-affinity GTPas¢. This GTPase stimulation was additive with that caused by the hormonal factors, prostaglandin E 1 and epinephrine, but not with thrombin. At concentrations higher than 1 raM, neomycin reduced control GTPas¢ activity and eliminated the stimulation caused by thrombin. The data suggest that neomycin by a presently unknown mechanism can regulate activity states of signal transducing GTP-binding proteins.

Neomycin does not interfere with the inositol phospholipid metabolism, but blocks binding of α-thrombin to intact human platelets

“…Both the decrease in binding and the thrombin-induced changes in inositol phospholipid metabolism can be reproduced by addition of the thrombin antagonist hirudin. The inhibitory action of neomycin on receptor-mediated cellular activation is therefore not related to the ability of the drug to bind to the phospholipase Chydrolysable inositol phospholipids, as claimed by most authors [7][8][9][10][11][12][13][14][15]. Neomycin has previously been shown to inhibit not only thrombin-induced platelet activation but also collagen-and platelet-activating-factor-induced aggregation and secretion [10].…”

“…In platelets only 10IUM was required [11], whereas in mast cells [12] and sea-urchin eggs [13] 1 mm was necessary to inhibit the agonist-induced breakdown of PIP2. Moreover, the data obtained by the use of neomycin have been difficult to interpret, since polyanionic molecules to which it binds also include inositol 1,4,5-trisphosphate and ATP [14], and at high concentrations the drug has even been shown to induce Ca2+ release and stimulate GTPases [15]. The specificity and the mechanism of the inhibitory effects of neomycin have therefore frequently been debated (reviewed in [16]).…”

Convulxin-induced platelet aggregation is accompanied by a powerful activation of the phospholipase C pathway

“…It has been suggested that stimulation of Cvx membrane sites may mediate platelet activation by stimulating effectors other than PLC, such as protein kinase C or a membrane Ca2`channel (Gerrard et al, 1989;O'Rourke et al, 1985). In fact, it cannot be excluded that neomycin, in addition to its ability to bind to phosphatidylinositol phosphates (Herrmann and Jakobs, 1988), regulates the activity state of membrane proteins such as Gproteins.…”

Interaction between Phosphoinositide-Phospholipase C and Phosphatidylcholine- Phospholipase D in Plasma Membranes of Retinal Capillary Pericytes

“…Under such a condition, neomycin, a PI-PLC inhibitor, significantly inhibited PC-PLD activity. Although neomy cin, an aminoglycoside antibiotic, is generally known for inhibiting PI-PLC by binding to inositol phospholipids [22,23], neomycin modifies the activity of platelet membrane GTPase [24] and induces high-affinity agonist binding of G protein-coupled receptors [25]. It also has been reported that neomycin inhib its GTPyS-induced histamine secretion and phosphatidic acid formation in permeabilized mast cells [26].…”