Ouabain Enhances Basal and Stimulus-Induced Cytoplasmic Calcium Concentrations in Platelets

Abstract

SummaryIncubation of platelet-rich plasma (PRP) with ouabain, an inhibitor of sodium/potassium ATPase (Na+/K+ ATPase), induced a significant rise in basal platelet intracellular calcium concentration ([Ca2+]i) when measured using fura 2. Ouabain induced an enhanced aggregation response to low doses of collagen in both PRP and washed platelets loaded with aequorin. In aequorin loaded platelets this enhanced aggregation response was associated with an enhanced rise in [Ca2+]j such that the relationship between [Ca2+]i and aggregation was unchanged. As inhibition of plasma membrane Na+/K+ ATPase would lead to a raised intracellular sodium ion concentration ([Na+]i) the results suggest that in the platelet, [Na+]i can modulate [Ca2+]i and hence influence the response of platelets to stimuli such as collagen.

Digitalis: a dangerous drug in atrial fibrillation? An analysis of the SPORTIF III and V data

“…Also, blood platelets are influenced: ouabain causes an increased aggregation after agonist stimulation in aggregometer studies 17. Whereas digitalis can activate platelets in vitro, that was not the case in our in vivo study in healthy young volunteers 18.…”

The plasma membrane calcium ATPase modulates calcium homeostasis, intracellular signaling events and function in platelets

“…As CE has been shown to inhibit Na + /K + ‐ATPase pumps [17] as well as PMCA, we investigated the effects of the Na + /K + ‐ATPase inhibitor ouabain on platelet aggregation. Concentrations of ouabain previously shown to inhibit Na + /K + ‐ATPases in platelets (1–10 μ m [18,19]) and excess concentrations (200 μ m ) had no effect on collagen‐induced or thrombin‐induced platelet aggregation (Fig. S4A,B).…”

Relocation of annexin V to platelet membranes is a phosphorylation-dependent process

“…Platelets from healthy volunteers were prepared as described previously [32] and suspended in Hepes-buffered Tyrode's solution (129 mM NaCl, 8.9 mM NaHCO $ , 2.8 mM KCl, 0.8 mM KH # PO % , 0.8 mM MgCl # , 5.6 mM dextrose and 10 mM Hepes\ NaOH, pH 7.4). The number of platelets and contaminating white blood cells were determined using a Coulter S Plus counter (courtesy of The Haematology Department, The General Infirmary NHS Trust, Leeds, U.K.).…”