KCNQ Current Contributes to Inspiratory Burst Termination in the Pre-Bötzinger Complex of Neonatal Rats in vitro.

Ann L Revill,Alexis Katzell,Christopher A Del Negro,Gregory D Funk,William K Milsom

doi:10.3389/fphys.2021.626470

Abstract

The pre-Bötzinger complex (preBötC) of the ventral medulla generates the mammalian inspiratory breathing rhythm. When isolated in explants and deprived of synaptic inhibition, the preBötC continues to generate inspiratory-related rhythm. Mechanisms underlying burst generation have been investigated for decades, but cellular and synaptic mechanisms responsible for burst termination have received less attention. KCNQ-mediated K+ currents contribute to burst termination in other systems, and their transcripts are expressed in preBötC neurons. Therefore, we tested the hypothesis that KCNQ channels also contribute to burst termination in the preBötC. We recorded KCNQ-like currents in preBötC inspiratory neurons in neonatal rat slices that retain respiratory rhythmicity. Blocking KCNQ channels with XE991 or linopirdine (applied via superfusion or locally) increased inspiratory burst duration by 2- to 3-fold. By contrast, activation of KCNQ with retigabine decreased inspiratory burst duration by ~35%. These data from reduced preparations suggest that the KCNQ current in preBötC neurons contributes to inspiratory burst termination.

Highlights

Inspiration is the dominant, active phase of the respiratory cycle in mammals
The activation of sodium currents or deactivation of Ih (Thoby-Brisson et al, 2000) would otherwise obscure KCNQ current, which we aimed to evoke with our voltage-clamp protocol
XE991 evoked an inward current that stabilized to the initial rate of decay

Summary

Introduction

Inspiration is the dominant, active phase of the respiratory cycle in mammals. Its rhythm emanates from the pre-Bötzinger complex (preBötC) of the ventrolateral medulla (Smith et al, 1991; Del Negro et al, 2018). The most recent models of inspiratory rhythm generation favor synaptic mechanisms where burstlets or bursts derive from the progressive recruitment and excitation of a critical subpopulation of Dbx1-derived, glutamatergic neurons and their increased synchronization in the pre-inspiratory and inspiratory phases (Del Negro et al, 2018; Ashhad and Feldman, 2020; Kallurkar et al, 2020). Under normal physiological conditions in many vertebrates, feedback from slowly adapting pulmonary stretch receptors plays an important role in terminating inspiration (Bonham et al, 1993). Most importantly, when stretch receptor feedback is removed by vagotomy for experimental preparations or due to medical necessity in Inspiratory Termination: Role of KCNQ humans with heart–lung transplants, inspiration is prolonged, but it still terminates (Lumsden, 1923; Smith et al, 1990; Bonham et al, 1993). Dorsolateral pontine networks normally contribute to inspiratory burst termination, but even the prolonged inspiratory (apneustic) events that emerge when these inputs are removed self-terminate (Lumsden, 1923; Stella, 1938; von Euler et al, 1976; Foutz et al, 1988; Feldman et al, 1992; Harris and Milsom, 2003)

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