Abstract
Observations of the electrophysiological properties of cells are important for understanding cellular functions and their underlying mechanisms. Short action potentials in axons are essential to rapidly deliver signals from the neuronal cell body to the terminals, whereas longer action potentials are required for sufficient calcium influx for transmitter release at the synaptic terminals and for cardiomyocyte and smooth muscle contractions. To accurately observe the shape and timing of depolarizations, it is essential to measure changes in the intracellular membrane potential. The ability to record action potentials and intracellular membrane potentials from mammalian cells and neurons was made possible by Ling and Gerard’s discovery in 1949, when they introduced sharp glass electrode with a submicron sized tip. Because of the small tip size, the sharp glass electrode could penetrate the cell membrane with little damage, which was one of the major breakthroughs in cellular electrophysiology and is the basic principle of the intracellular recording technique to date, providing the basis for further innovation of patch-clamp electrophysiology. I report a proof-of-principle demonstration of a novel method for recording intracellular potentials without penetrating the cell membrane using glass electrodes. We discovered that magnetically held transmembrane conductive nanoparticles can function as an intracellular electrode to detect transmembrane membrane potentials similar to those obtained by the conventional patch-clamp recording method.NEW & NOTEWORTHY To accurately observe the shape of action potentials, it is essential to perform intracellular recordings. I present a method to record intracellular potentials using magnetically held magnetic conductive nanoparticles in the membrane as an electrode. These nanoparticles function similarly to a conventional intracellular microelectrode. This is the first report to apply conductive nanoparticles to detect action potentials in the form of electrical signals.
Highlights
Bioactivities in the brain and heart are studied by measuring complex electrical signals in the form of extracellular compound action potentials using electroencephalography and electrocardiography, respectively
We considered that if conductive nanoparticles could be held across a cell membrane, they could provide a minimally disruptive, low-resistance pathway across the membrane to allow the detection of changes in intracellular membrane potentials
Because extracellular signals are differentials of membrane potential changes, and small-amplitude events are masked by the baseline noise, slow membrane potential changes and the resting membrane potential are not detected/determined under this method
Summary
Because of the small tip size, the sharp glass electrode could penetrate the cell membrane with little damage, which was one of the major breakthroughs in cellular electrophysiology and is the basic principle of the intracellular recording technique to date, providing the basis for further innovation of patch-clamp electrophysiology. The sharp electrode method is adapted for almost all conceivable cell types from unicellular organisms to neurons in the living brain (Verkhratsky and Parpura 2014) and is the basic principle of the intracellular recording technique to date Another technical breakthrough came when Neher and Sakmann (1976) developed the patch-clamp technique that detects ionic current movements through single ion channels, which are the building blocks that shape action potentials. I present a proof-of-principle demonstration of how magnetically held transmembrane conductive nanoparticles can function as an intracellular voltage sensor to detect transmembrane membrane potentials in cultured cells
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