Biology subjects

Pantazis, A.

Publications and source records attributed to Pantazis, A..

5 recordsLinked to original sources

bioRxiv2025

Two-step voltage-sensor activation of the human KV7.4 channel and effect of a deafness-associated mutation

Voltage-gated, potassium-selective KV7.4 channels are expressed in the inner ear and are crucial for hair-cell function and survival. Loss-of-function variants of KCNQ4, the gene encoding KV7.4-channel subunits, cause non-syndromic progressive hearing loss (DFNA2). KV7.4 opening requires a voltage-dependent conformational change (activation) of the charged voltage-sensor domains (VSDs), and its transduction to the pore. Previously, fast charge displacement was reported during VSD activation at negative potentials, but it is unclear how this is coupled to slow channel opening occurring at more depolarized potentials. Here, we optically tracked KV7.4 VSD activation with voltage-clamp fluorometry, leveraging two different fluorophores and pulsed excitation, to thoroughly characterize VSD movements. We found that VSD activation comprises several voltage-dependent transitions, some of which had kinetics and voltage-dependence matching those of channel opening and closing. The deafness-associated mutation R216H, which substitutes a charged amino-acid in the VSD, impaired both VSD movements and channel opening, shifting them towards more depolarized potentials. This suggested that R216H impaired KV7.4 function by destabilizing VSD activation. Using molecular dynamics, we found that H216 reduced intramolecular interactions, thus decreasing the stability of an active VSD conformation. We propose that the KV7.4 VSD activates in two steps: a fast movement at negative voltages that represents a first transition to an intermediate state of activation; and this is followed by slower, depolarized component that represents subsequent full VSD activation, which drives channel opening.

biophysics↗

bioRxiv2024

A rich conformational palette underlies human CaV2.1-channel availability

Depolarization-evoked opening of CaV2.1 (P/Q-type) Ca2+-channels triggers neurotransmitter release, while voltage-dependent inactivation (VDI) limits channel availability to open, contributing to synaptic plasticity. The mechanism of CaV2.1 response to voltage is unclear. Using voltage-clamp fluorometry and kinetic modeling, we optically tracked and physically characterized the structural dynamics of the four CaV2.1 voltage-sensor domains (VSDs). VSD-I seems to directly drive opening and convert between two modes of function, associated with VDI. VSD-II is apparently voltage-insensitive. VSD-III and VSD-IV sense more negative voltages and undergo voltage-dependent conversion uncorrelated with VDI. Auxiliary {beta}-subunits regulate VSD-I-to-pore coupling and VSD conversion kinetics. CaV2.1 VSDs are differentially sensitive to voltage changes brief and long-lived. Specifically the voltage-dependent conformational changes of VSD-I are linked to synaptic release and plasticity.

neuroscience↗

bioRxiv2024

Electrical and G-protein Regulation of CaV2.2 (N-type) Channels

How G-proteins inhibit N-type, voltage-gated, calcium-selective channels (CaV2.2) during presynaptic inhibition is a decades-old question. G-proteins G{beta}{gamma} bind to intracellular CaV2.2 regions, but the inhibition is voltage-dependent. Using the hybrid electrophysiological and optical approach voltage-clamp fluorometry, we show that G{beta}{gamma} acts by selectively inhibiting a subset of the four different CaV2.2 voltage-sensor domains (VSDs I-IV). During regular "willing" gating, VSDs I and IV activation resemble pore opening, VSD III activation is hyperpolarized, and VSD II appears unresponsive to depolarization. In the presence of G{beta}{gamma}, CaV2.2 gating is "reluctant": pore opening and VSD-I activation are strongly and proportionally inhibited, VSD IV is modestly inhibited while VSD III is not. We propose that G{beta}{gamma} inhibition of VSD-I and -IV underlies reluctant CaV2.2 gating and subsequent presynaptic inhibition.

neuroscience↗

bioRxiv2019

Circuit-Specific Early Impairment of Proprioceptive Sensory Neurons in the SOD1G93A Mouse Model for ALS

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease in which motor neurons degenerate resulting in muscle atrophy, paralysis and fatality. Studies using mouse models of ALS indicate a protracted period of disease development with progressive motor neuron pathology, evident as early as embryonic and postnatal stages. Key missing information includes concomitant alterations in the sensorimotor circuit essential for normal development and function of the neuromuscular system. Leveraging unique brainstem circuitry, we show in vitro evidence for reflex circuit-specific postnatal abnormalities in the jaw proprioceptive sensory neurons in the well-studied SOD1G93A mouse. These include impaired and arrhythmic action potential burst discharge associated with a deficit in Nav1.6 Na+ channels. However, the mechanoreceptive and nociceptive trigeminal ganglion neurons and the visual sensory retinal ganglion neurons were resistant to excitability changes in age matched SOD1G93A mice. Computational modeling of the observed disruption in sensory patterns predicted asynchronous self-sustained motor neuron discharge suggestive of imminent reflexive defects such as muscle fasciculations in ALS. These results demonstrate a novel reflex circuit-specific proprioceptive sensory abnormality in ALS.\n\nSignificance StatementNeurodegenerative diseases have prolonged periods of disease development and progression. Identifying early markers of vulnerability can therefore help devise better diagnostic and treatment strategies. In this study, we examined postnatal abnormalities in the electrical excitability of muscle spindle afferent proprioceptive neurons in the well-studied SOD1G93A mouse model for neurodegenerative motor neuron disease, ALS. Our findings suggest that these proprioceptive sensory neurons are exclusively afflicted early in the disease process relative to sensory neurons of other modalities. Moreover, they presented Nav1.6 Na+ channel deficiency which contributed to arrhythmic burst discharge. Such sensory arrhythmia could initiate reflexive defects such as muscle fasciculations in ALS as suggested by our computational model.

neuroscience↗

bioRxiv2018

A Mechanism of Real-Time Noise Modulation in Neurons

Uncertainties pose an ongoing challenge for information processing in the nervous system. It is not entirely clear how neurons maintain dynamic stability of information, encoded in the temporal features of spike trains, notwithstanding stochastic influences. Here we examined the contribution of subclasses of membrane sodium currents in real-time noise modulation in sensory neurons. Fast sodium (Na+) currents are essential for spike generation, and a persistent Na+ current can entrain preferred input frequencies via membrane resonance. Using mathematical modeling, theory and experiments, we show that a resurgent Na+ current can stabilize the temporal features of burst discharge and confer noise tolerance. These novel insights reckon the role of biophysical properties of Na+ currents beyond mere spike generation. Instead, these mechanisms might be how neurons perform real-time signal processing to maintain order and entropy in neural discharge. Our model analysis further predicts a negative feedback loop in the molecular machinery of an underlying Nav1.6-type Na+ channel gating considered in this study.

neuroscience↗