The Platelet Electrome: Evidence for a Role in Regulation of Function and Surface Interaction

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.

Cytoplasmic anion/cation imbalances applied across the membrane capacitance may form a significant component of the resting membrane potential of red blood cells

“…In previous work with RBCs 12 , and subsequently confirmed with platelets 13 , we demonstrated that modulation of V m alters the ζ-potential. In consequence, developing an understanding of the origin of V m is essential to understand how this relationship occurs.…”

“…Furthermore, recent observations of red blood cells (RBCs) have indicated that the extracellular ζ-potential (a voltage field that arises from a cell surface charge and extends several nanometres from the cell surface) is affected by V m , via a process related to the capacitance of the electrical double-layer 11 . Similar phenomena have also been identified in platelets 12 . Connections have also been identified between V m and passive cellular electrical properties, such as the cytoplasm conductivity σ cyto and the membrane conductance G eff [13][14][15] .…”

“…One possible origin is the relationship between charge in the cell interior, and the effect of this charge on the transmembrane capacitance. The conventional relationship between voltage V , charge Q and capacitance C ( V = Q / C ) allows estimation of the effect of anionic and cationic charge imbalances in the inner double layer, compared to the external medium, and the double layer capacitance as derived previously 12 . This yields the expression: where 1/ κ is the Debye length; the number of ions per m 3 for a medium conductivity of 1 S m −1 , and A as defined in Eq.…”

“…The models in this paper were derived using the data set presented in a prior study 12 on RBC electrical properties. In summary, data were produced by simultaneous measurement of the ζ-potential via a Malvern Zetasizer Nano (Malvern UK); membrane capacitance and conductance, as well as cytoplasm conductivity by dielectrophoresis 14 , 35 using a Deparator 3DEP (Heathfield UK) 33 ; and membrane potential, V m , via the CCCP method, by measuring medium pH (Hanna Instruments, Leighton Buzzard, UK) after treatment with a proton ionophore, a technique that has been widely used for V m measurement in RBCs 36 .…”

Circadian rhythmicity in murine blood: Electrical effects of malaria infection and anemia

“…DEP has revealed circadian cycles in the electrical properties of RBCs ( Henslee et al, 2017 ; Beale et al, 2019 ; Beale et al, 2022 ) human as well as sub-2 h, ultradian rhythms in the RBCs of voles ( Hoettges et al, 2019 ). More recently, connections have been demonstrated between these DEP-derived electrical parameters and other electrical measures of cell function, such as the membrane potential (V m ) and the extracellular electrical potential (the ζ-potential) that regulates the way cells interact with other cells and biological entities in their immediate environment ( Hughes et al, 2021 ; Hughes et al, 2022 ).…”