Gating currents

Abstract

Many membrane proteins sense the voltage across the membrane where they are inserted, and their function is affected by voltage changes. The voltage sensor consists of charges or dipoles that move in response to changes in the electric field, and their movement produces an electric current that has been called gating current. In the case of voltage-gated ion channels, the kinetic and steady-state properties of the gating charges provide information of conformational changes between closed states that are not visible when observing ionic currents only. In this Milestone, the basic principles of voltage sensing and gating currents are presented, followed by a historical description of the recording of gating currents. The results of gating current recordings are then discussed in the context of structural changes in voltage-dependent membrane proteins and how these studies have provided new insights on gating mechanisms.

Optical measurement of voltage sensing by endogenous ion channels

“…Steps to 0 mV resulted in unlabeling of CHO cells (Fig 4) and neurons (Fig 8), and the kinetics 5 of this unlabeling were similar (Fig 8 K). The punctate GxTX-594 labeling of CA1 neurons is 6 consistent with the patterns of endogenous Kv2 expression seen by immunofluorescence 7 (Misonou et al 2005, Bishop et al 2015, 2018, and Kv2.1-GFP expression (Fig 7). Together, 8 these results are consistent with the GxTX-594 probe labeling endogenous Kv2 channels in rat 9 CA1 hippocampal pyramidal neurons and unlabeling in response to voltage activation of the 10 channels.…”

“…Kv2 channels are expressed in most central neurons and localize 13 to cell bodies, proximal dendrites, and the axon initial segment (Trimmer 1991, Scannevin et al 14 1996, Du et al 1998, Murakoshi & Trimmer 1999, Lim et al 2000, Kihira et al 2010, King et 15 al. 2014, Bishop et al 2015, 2018. When Kv2 channels contribute to 16 action potential repolarization, they modulate neuronal excitability (Du et al 2000, Blaine & 17 Ribera 2001, Liu & Bean 2014, Speca et al 2014, Kimm et al 2015, Hönigsperger et al 2017, 18 Palacio et al 2017.…”

“…Thus, 21 measuring whether Kv2 voltage sensors adopt resting versus active conformations determines 22 whether a prerequisite for opening has occurred, and reveals the conformational state of 23 nonconducting Kv2 proteins that may be coupled to other physiological outputs. 24 25 Conformational changes of voltage sensors have been detected with electrophysiological 26 measurements of gating currents (Armstrong & Bezanilla 1973, M. F. Schneider & Chandler 27 1973, Bezanilla 2018 or by optical measurements from fluorophores covalently attached to 28 voltage sensors by genetic encoding (Lin & Schnitzer 2016) and/or chemical engineering (G. 29 Zhang et al 2015). Each of these techniques have enabled breakthroughs in our understanding of 30 how protein conformational changes are coupled to one another (J.…”

Excitation of murine cardiac myocytes by nanosecond pulsed electric field

“…27,28 Although gating at the single molecule level might be a "jump process" between discrete states, 28,29 with probability increased by depolarization, nsPEF-induced depolarization may be too brief to open the critical number of channels to trigger an AP. Such stimuli may be too brief to elicit APs directly by membrane depolarization, since the process of opening of voltage-gated sodium channels, as evidenced by the time course of gating currents, takes tens to hundreds of microseconds.…”

“…Such stimuli may be too brief to elicit APs directly by membrane depolarization, since the process of opening of voltage-gated sodium channels, as evidenced by the time course of gating currents, takes tens to hundreds of microseconds. 27,28 Although gating at the single molecule level might be a "jump process" between discrete states, 28,29 with probability increased by depolarization, nsPEF-induced depolarization may be too brief to open the critical number of channels to trigger an AP. It suggests that there might be a coupling mechanism to link nsPEF and AP generation.…”