Prediction of Local pH Variations during Amperometric Monitoring of Vesicular Exocytotic Events at Chromaffin Cells

Abstract

Electrochemical monitoring of the exocytosis process is generally performed through amperometric oxidation of the electroactive messengers released by single living cells. Herein, we consider the vesicular release of catecholamines by chromaffin cells. Each exocytotic event is thus detected as a current spike whose morphology (intensity, duration, area, etc.) features the efficiency of the secretion process. However, the electrochemical oxidation of catechols produces quinone derivatives and protons. As a consequence, unless specific mechanisms may be adopted by a cell to regulate the pH near its membrane, the local pH between the cell membrane and the electrode necessarily drops within the electrode-cell cleft. Though this consequence of amperometric detection is generally ignored, it has been investigated in this work through simulation of the local pH drop created during the amperometric recording of a sequence of exocytotic events. This was performed based on frequencies and magnitudes of release detected at chromaffin cells. The corresponding acidification was shown to severely depend on the microelectrode radius. For usual 10 μm diameter carbon fiber electrodes, pH values below six were predicted to be reached within the electrode-cell cleft after monitoring a few current spikes.

Progress in transparent diamond microelectrode arrays

“…In this way action potentials from cardiac tissue samples could be detected with a background noise <20 μV p–p. Also variation of chemical potential (pH) following cell activity , could be clearly resolved, in accordance with the pH‐sensitivity shown by oxygen‐terminated diamond electrodes . This latter sensing capability rounds‐up the already mentioned outstanding properties of diamond, making of it an unsurpassed multitalented material for microelectrodes.…”

Styrylsulfonates and ‐Sulfonamides through Pd‐Catalysed Matsuda–Heck Reactions of Vinylsulfonic Acid Derivatives and Arenediazonium Salts

“…Similar conclusions have previously been drawn from mechanistic investigations into Heck reactions of aryl iodides on the basis of competition experiments and kinetic studies. [115][116][117] These experiments show that acrylates react faster and with far higher regioselectivity than styrenes in the insertion step, a result of the positively polarized position. On the other hand, observations by Myers and coworkers point to a slower -hydride elimination if electron-withdrawing substituents are attached to the α position (this observation can be rationalized by assuming that a certain degree of back-donation from the metal into the σ* orbital of the C-H bond is required to trigger the cleavage of this bond).…”

“…Similar five-membered chelate complexes formed through a dynamic equilibrium of -hydride elimination and reinsertion have been observed spectroscopically during mechanistic investigations into the Heck reactions of acrylates. [114][115][116] In these examples, however, the Pd hydride was stabilized by phosphine ligands. While effective catalyst inhibition through the formation of a five-membered chelate appears to be far more plausible than inhibition through the formation of the alternative four-membered chelate (i.e., G), the crucial cationic Pd-hydride species F should be short-lived in our case, because no stabilizing ligands are present.…”

Simulations of amperometric monitoring of exocytosis: moderate pH variations within the cell-electrode cleft with the buffer diffusion

“…[25][26][27][28] This issue was addressed in a previous theoretical work confirming that the electrochemically induced acidification should occur and depends on the electrode size as well as the exocytotic frequency. 29 However, such results were sometimes inconsistent with experimental results evidencing that the electrode surface area did not modify the amperometric spikes features. In this paper, we report on a fundamental modification of this previous model that now takes into account the diffusion of the buffer and its ability to be replenished with the cell-electrode cleft with its diffusion.…”