Functional relevance of anaerobic metabolism in the isolated respiratory network of newborn rats

Abstract

Respiratory (C₃–C₅) activity and extracellular K⁺, pH and Ca²⁺ (aK_e, pH_e, [Ca]_e, respectively) in the ventral respiratory group (VRG) were measured in vitro. In brainstem-spinal cord preparations from 0- to 1 -day-old rats, lowering of bath glucose content from 30 to 10 mM for 1 h did not affect aK_e or rhythmic activity. In preparations from 2- to 3-day-old animals, however, an aK_e rise by about 1 mM and disturbance of rhythm occurred after a delay of 50 min. Glucosefree saline resulted, after about 30 min, in reversible blockade of respiratory rhythm and an aK_e rise by more than 8 mM, whereas pH_e remained unaffected. Exposure to anoxia for 30 min after 1 h of pre-incubation in 10 mM glucose led to a progressive rise of aK_e, and a fall of [Ca]_e. The concomitant suppression of rhythm was irreversible in preparations from 2- to 3-day-old animals. Similar effects on aK_e and [Ca]_e and irreversible blockade of rhythm were revealed during anoxia in glucose-free solution, or by addition of 2–5 mM iodoacetate to oxygenated or hypoxic solutions. Iodoacetate led to a slow increase of pH_e by more than 0.2 pH units, which was accelerated by anoxia. Our findings show that normal respiratory network functions in the en bloc medulla, in particular from rats older than 1 day, depend on high bath glucose levels, necessary for effective utilization of anaerobic metabolism.