Abstract
Introduction. Platelets protect the body from injury through formation of blood clots, changing from a normal, quiescent state to become “activated” in response to external stimuli such as chemical cues, shear stress and temperature. This causes changes in shape, increased adhesion, and alteration of the electrical properties such as membrane potential Vm and zeta potential ζ. These phenomena have been regarded as largely unconnected; for example, changes in ζ have been attributed solely to alteration of surface lipid concentration. However, recent reports suggest that cells can alter ζ electrostatically by alteration of Vm in red blood cells. We hypothesised that if platelets also modulate ζ via Vm, this may provide an alternative mechanism to alter cell-cell interaction.
Methods. We investigated platelets stored at different temperatures (4°C, 22°C, 37°C) for 24h, which is known to alter platelet behaviour and electrical properties, and compared these with analyses of freshly-harvested platelets. These four conditions exhibited unique sets of electrical properties (Vm, ζ, membrane conductance Geff and cytoplasm conductivity σcyto) as well as surface exposure of the adhesion molecule P-Selectin. These were analysed to identify correlations between electrical parameters and platelet activation state.
Results. Many parameters exhibit pairwise correlation across all four conditions, in particular between ζ and Geff, and also between Vm and σcyto. Furthermore, when the electrical behaviour of platelets stored at 4°C (known to activate the cells) was removed from the analysis, additional relationships were observed among the remaining conditions, including those connecting ζ and Vm to the amount of P-selectin binding.
Conclusion. Results suggest that Vm may mechanistically alter the availability of cationic molecules at the cell surface, a process never reported before, with implications for our wider understanding of cell-molecule and cell-cell interaction.