Interaction between CO2 and citrate ions in medullary reticular formation

Abstract

Ventilation was recorded in anesthetized rats during the injection of small quantities of Na citrate solution near the obex and during the application of electric pulses to the same region. Increases in Ve or ventilatory arrest were typical responses to these stimuli. Observations were made to determine whether either response could be altered by the inhalation of 10% CO2 or 7% O2 gas mixtures. Responses to 1.8 µl 2.8 mm Na citrate injections were diminished from controls while the animals were hyperventilating during CO2 administration. In contrast, ventilatory responses to 1.4 mm Na citrate injections were potentiated during hyperventilation resulting from 7% O2. Thus, hypercapnia depressed and hypoxia enhanced the excitability of those neurons of the medullary reticular formation which respond to citrate. The stabilizing action of calcium on the neurons is almost certainly removed by citrate. Several other carbohydrate intermediates besides citrate bind calcium ions as well. It is proposed that CO2 under certain conditions might thereby regulate the repetitive discharge of certain groups of neurons in the medullary reticular formation.