Search bioRxiv⌕ Search
Home/Archive/bioRxiv

bioRxiv · 10.1101/2020.10.31.363341

Fast inactivation of Na+ current in rat adrenal chromaffin cells involves two independent inactivation pathways

Martinez-Espinosa, P. L.·Neely, A.·Ding, J.·Lingle, C. J.
View original source ↗Export metadata ↓

Abstract

Voltage-dependent sodium (Nav) current in adrenal chromaffin cells (CCs) is rapidly inactivating and TTX-sensitive. The fractional availability of CC Nav current has been implicated in regulation of action potential (AP) frequency and the occurrence of slow-wave burst firing. To ascertain whether features of CC Nav inactivation might influence AP firing, we recorded Nav current in rat CCs, primarily from adrenal medullary slices. A key feature of CC Nav current is that recovery from inactivation, even following brief (5 ms) inactivation steps, exhibits two exponential components of generally similar amplitude. Variations of standard paired pulse protocols support the view that entry into the fast and slower recovery processes result from largely independent, competing inactivation pathways, both of which occur with similar onset times at depolarizing potentials. Over voltages from -120 to -80 mV, faster recovery varies from ~3 to 30 ms, while slower recovery from about 50-400 ms. At strong activation voltages (+0 mV and more positive), the relative entry into slow or fast recovery pathways is similar and independent of voltage. Trains of brief inactivating steps result in cumulative increases in the slower recovery fraction. This supports idea that brief recovery intervals preferentially allow recovery of channels from fast recovery pathways, thereby increasing the fraction of channels in the slow recovery pathway with each subsequent inactivation step. This provides a mechanism whereby differential rates of recovery produce use-dependent accumulation in slower recovery pathways. Consistent with use-dependent accumulation of channels in slow recovery pathways, repetitive AP clamp waveforms at 1-10 Hz frequencies reduce Nav availability to 10-20% of initial amplitude dependent on holding potential. The results indicate that there are two distinct pathways of fast inactivation, one that leads to normal fast recovery and the other with a slower time course, which together are well-suited to mediate use-dependent changes in Nav availability.

Source connections

Explore related subjects

biophysicsPreprint

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Martinez-Espinosa, P. L., Neely, A., Ding, J., Lingle, C. J.. 2020-11-01. Fast inactivation of Na+ current in rat adrenal chromaffin cells involves two independent inactivation pathways. https://doi.org/10.1101/2020.10.31.363341

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

Frequency-Dependent Structural Responses of Amyloid-β Fibrils to Terahertz Pulses: A Nonequilibrium Molecular Dynamics Study

The abnormal aggregation of amyloid proteins into fibrils is closely associated with several neurodegenerative diseases, highlighting the importance of developing effective strategies to modulate fibril structural stability. Here, we employed nonequilibrium molecular dynamics(NEMD) simulations to examine the effects of intense terahertz-to-mid-infrared pulses on three amyloid fibrils (2LMP, 2MXU, and 5OQV), focusing on the combined effects of pulse frequency and electric-field strength. Frequency scans from 0.5 to 60 THz in 0.5 THz steps revealed frequency-dependent losses of {beta}-sheet content, with several common response patterns in these fibrils. Comparisons at 2, 23, 33, and 50 THz showed that pulse-induced changes in secondary structure differed from those in high-temperature controls. Hydrogen-bond analysis showed that total hydrogen-bond counts could partially recover even as interchain hydrogen bonds continued to decrease, with distinct responses among representative chain pairs. We therefore propose a two-threshold electric-field framework for fibril disruption: Eth1 describes the onset of structural perturbation, whereas Eth2 indicates persistent structural loss after the pulse. This framework offers a testable approach for characterizing amyloid structural responses to external fields, although the underlying energy-coupling mechanisms, quantitative thresholds, and long-term recovery require further validation. These findings may provide a theoretical basis for exploring external-field-based strategies to modulate protein aggregation.

biophysics↗
bioRxiv2026

Organised streaming of cerebrospinal fluid in the human third ventricle

Quasi-periodic pressure pulses associated with cardiac and respiratory activity generate reciprocating cerebrospinal fluid (CSF) motion in the human ventricles. Regular waves dominated by the cardiac cycle are overlaid with cycles of low-frequency respiratory waves, the latter to become stronger in forced breathing or even dominated by large successive flushes in NREM sleep. The present study investigates how such waves contribute to residual streaming within the human ventricles. Transient CFD simulations were performed in the third ventricle at varying parameters of frequency, stroke volume and wave-form asymmetry. Increasing the aqueduct peak Reynolds-number, either by small stroke volume and high frequency or large stroke volume at low frequency, transfers the flow from a reversible flow pattern to the formation of clear preferential pathways, alternating between the in- and outflow cycle. The resulting permanent streaming flux across the aqueduct relative to the mean oscillatory flow-rate, i.e. the dimensionless streaming ratio SR follows a rational saturation relation, SR [~] ReAq,peak/(C + ReAq,peak), demonstrating that increasing the peak aqueduct Reynolds number yields diminishing returns and bounds the relative contribution of residual inter-ventricular streaming. These findings demonstrate differences in hydrodynamic organisation in the third ventricle and highlight the importance of this organisation for intraventricular fluid exchange.

biophysics↗
bioRxiv2026

Amyloid stability and condensate material properties independently govern the hnRNPA2 condensate to fibril transition

hnRNPA2 is a component of cellular membraneless organelles many of which contain RNA and RNA-binding proteins (RBPs). RBPs frequently contain low-complexity domains (LCDs) that can also assemble into amyloid fibrils. Fibrils isolated from patients with frontotemporal lobar degeneration contain ordered segments of these LCDs and disease-associated mutations can enhance the homotypic interactions that promote aggregation. Although previous studies have largely examined the condensate-to-fibril transition by altering condensate stability, how amyloid structure governs this process remains poorly understood. Here, we show that the hnRNPA2 LCD forms a reproducible fibril fold and by combining structure-guided thermodynamic profiling, peptide design, mutagenesis and in vitro characterization under conditions with (two-phase) and without (one-phase) condensates, we define the molecular determinants of its assembly. We identify an aromatic triad within the fibril core that controls fibril formation kinetics and thermodynamic stability. Mutational analysis further reveals that condensate stability and fibril stability are largely independent. Finally, microrheology linked reduced condensate viscosity to faster fibril formation, supporting a role for condensate material properties in regulating aggregation kinetics. Together, these findings support a model in which the condensate-to-fibril transition is governed by the interplay between a disordered ''fuzzy coat'' and a fibril-forming aromatic triad within hnRNPA2. This work provides a structural framework for understanding how condensates can transition into amyloid assemblies.

biophysics↗