Two firing modes and well-resolved Na+, K+, and Ca2+ currents at the cell-microelectrode junction of spontaneously active rat chromaffin cell on MEAs

Abstract

We recorded spontaneous extracellular action potentials (eAPs) from rat chromaffin cells (CCs) at 37 °C using microelectrode arrays (MEAs) and compared them with intracellularly recorded APs (iAPs) through conventional patch clamp recordings at 22 °C. We show the existence of two distinct firing modes on MEAs: a ~ 4 Hz irregular continuous firing and a frequent intermittent firing mode where periods of high-intraburst frequency (~ 8 Hz) of ~ 7 s duration are interrupted by silent periods of ~ 12 s. eAPs occurred either as negative- or positive-going signals depending on the contact between cell and microelectrode: either predominantly controlled by junction-membrane ion channels (negative-going) or capacitive/ohmic coupling (positive-going). Negative-going eAPs were found to represent the trajectory of the Na+, Ca2+, and K+ currents passing through the cell area in tight contact with the microelectrode during an AP (point-contact junction). The inward Nav component of eAPs was blocked by TTX in a dose-dependent manner (IC50 ~ 10 nM) while the outward component was strongly attenuated by the BK channel blocker paxilline (200 nM) or TEA (5 mM). The SK channel blocker apamin (200 nM) had no effect on eAPs. Inward Nav and Cav currents were well-resolved after block of Kv and BK channels or in cells showing no evident outward K+ currents. Unexpectedly, on the same type of cells, we could also resolve inward L-type currents after adding nifedipine (3 μM). In conclusion, MEAs provide a direct way to record different firing modes of rat CCs and to estimate the Na+, Ca2+, and K+ currents that sustain cell firing and spontaneous catecholamines secretion.

From Finite Element Simulations to Equivalent Circuit Models of Extracellular Neuronal Recording Systems Based on Planar and Mushroom Electrodes

“…As a support to this claim, fitting of extracellular recordings suggested accumulation/depletion of ion channels (e.g., K + , Na + ) in rat hippocampal [49], cortical [30] and dorsal root [50] neurons, HEK293 cells [51], human myocardial cells [52]. Furthermore, ion channels can drift-diffuse across the cell membrane [47] and different shapes of extracellular recorded signals are also observed across excitable cells without arborizations, such as chromaffin cells [53]. To reproduce these putative uneven distributions of channels, we alter the maximum channel conductance g X i of ion species X i in (7) by multiplication for the scalar µ X i , similarly to [50].…”

Deletion of the α2δ‐1 calcium channel subunit increases excitability of mouse chromaffin cells

“…The spontaneous electrical activity reported in isolated mouse (Marcantoni et al., 2009) and rat (Marcantoni et al., 2023) CCs as well as mouse (Milman et al., 2021; Nassar‐Gentina et al., 1988; Voets et al., 1999) and rat adrenal gland slices (Albinana et al., 2015; Barbara et al., 1998; Kajiwara et al., 1997; Lopez Ruiz et al., 2022; Martin et al., 2001, 2003) might be responsible for tonic CA release. However, sympathetic nervous system activation lead to MCCs nicotinic ACh receptor‐mediated Na + influx and rapid membrane depolarization that neurogenically augments the electrical activity and vesicle exocytosis.…”

From Finite Element Simulations to Equivalent Circuit Models of Extracellular Neuronal Recording Systems based on Planar and Mushroom Electrodes

“…K + , Na + ) in rat hippocampal [50], cortical [30] and dorsal root [42] neurons, HEK293 cells [51], human myocardial cells [52]. Furthermore, ion channels can drift-diffuse across the cell membrane [48] and different shapes of extracellular recorded signals are also observed across excitable cells without arborizations, such as chromaffin cells [53]. To reproduce these putative uneven distributions of channels, we alter the maximum channel conductance g X i of ion species X i in (7) by multiplication for the scalar µ X i , similarly to [42].…”