Background sodium current stabilizes bursting in respiratory pacemaker neurons.

Area of Science:

• Neuroscience
• Computational Neuroscience
• Physiology

Background:

• Rhythmic behaviors like respiration depend on endogenous pacemaker properties.
• Background currents are crucial for maintaining pacemaker membrane potential within a bursting range, stabilizing rhythmogenesis.
• Previous work showed respiratory pacemakers resist hyperpolarization, hinting at a stabilizing background current.

Purpose of the Study:

• To elucidate the ionic basis of the stabilizing background current in respiratory pacemakers.
• To determine the role of this background current in maintaining respiratory rhythmogenesis.

Main Methods:

• Utilized low extracellular sodium (Na+) artificial cerebrospinal fluid (ACSF) to isolate ionic contributions.
• Performed current-clamp studies on synaptically isolated respiratory pacemaker neurons.
• Investigated the effects of hyperpolarizing current injection, I(h)-current blockers, tetrodotoxin, and altered extracellular potassium ([K+](o)) concentrations.

Main Results:

• In low-[Na+](o) ACSF, pacemakers hyperpolarized, lost bursting ability, and failed to depolarize during hyperpolarizing current injection.
• The depolarizing shift and resumption of bursting during hyperpolarization were abolished in low-[Na+](o) ACSF but persisted with I(h)-blockers, indicating a sodium-dependent mechanism.
• This sodium current was necessary for maintaining membrane potential within the bursting range, with interactions observed with extracellular potassium levels.

Conclusions:

• Respiratory pacemaker neurons possess a background sodium current essential for stabilizing membrane potential.
• This background sodium current actively maintains the membrane potential within a range conducive to bursting activity.
• The identified sodium current is critical for stabilizing respiratory rhythmogenesis.