Ultrasensitive Diamond Microelectrode Application in the Detection of Ca2+ Transport by AnnexinA5-Containing Nanostructured Liposomes

Abstract

This report describes the innovative application of high sensitivity Boron-doped nanocrystalline diamond microelectrodes for tracking small changes in Ca2+ concentration due to binding to Annexin-A5 inserted into the lipid bilayer of liposomes (proteoliposomes), which could not be assessed using common Ca2+ selective electrodes. Dispensing proteoliposomes to an electrolyte containing 1 mM Ca2+ resulted in a potential jump that decreased with time, reaching the baseline level after ~300 s, suggesting that Ca2+ ions were incorporated into the vesicle compartment and were no longer detected by the microelectrode. This behavior was not observed when liposomes (vesicles without AnxA5) were dispensed in the presence of Ca2+. The ion transport appears Ca2+-selective, since dispensing proteoliposomes in the presence of Mg2+ did not result in potential drop. The experimental conditions were adjusted to ensure an excess of Ca2+, thus confirming that the potential reduction was not only due to the binding of Ca2+ to AnxA5 but to the transfer of ions to the lumen of the proteoliposomes. Ca2+ uptake stopped immediately after the addition of EDTA. Therefore, our data provide evidence of selective Ca2+ transport into the proteoliposomes and support the possible function of AnxA5 as a hydrophilic pore once incorporated into lipid membrane, mediating the mineralization initiation process occurring in matrix vesicles.

Frenkel-Poole Mechanism Unveils Black Diamond as Quasi-Epsilon-Near-Zero Surface

“…We infer that highly defected surfaces with shallow electron traps may behave towards electromagnetic waves in a similar manner to the previously mentioned degenerated semiconductors. Even if this physical phenomenon should be confirmed by specific electromagnetic experiments, this is the first scientific report on quasi-ENZ effect on a diamond substrate up to our knowledge, and it can be useful to the large community of scientists working on diamond devices, from biosensors [ 29 , 30 , 31 , 32 ] to dosimeters [ 33 , 34 ] and to quantum computing [ 35 , 36 ]. In fact, as easy examples, the localized implementation of ENZ surfaces on diamonds gives the opportunity to improve optical interconnections between individual quantum building blocks (see Figure 2 ) or to improve nanoantennas radiation emission efficiency [ 19 ].…”

Annexin A5 stabilizes matrix vesicle-biomimetic lipid membranes: unravelling a new role of annexins in calcification

“…A recent study suggested that Annexin A5 might also take part in Ca 2+ uptake by matrix vesicles. Pasquarelli and co-workers recently described that the self-assembly of annexin A5 in the vesicles’ membrane may create a hydrophilic pore that can be exploited by the vesicles to accumulate Ca 2+ in the lumen (Pasquarelli et al 2022 ). However, the lack of transmembrane domains, the lower efficiency of Ca 2+ transport compared with specific ionophores, and the fact that annexin A5 is present in higher amounts than other identified transporters in the membrane of matrix vesicles, makes it difficult to address Ca 2+ transport as being its primary role in mineralization (Wuthier and Lipscomb 2011 ).…”