INFLUENCE OF CALCIUM AND MAGNESIUM ON RESPIRATORY RESPONSE TO CHANGES IN CSF PH

The ventral surface of the medulla oblongata of anesthetized cats was superfused with fluids of different Ca++ and Mg++ concentration and pH. The effects of altered composition of the superfusing fluids on respiration were studied. A three-fold increase of the reference Ca++ concentration (1.5 meq/1) in the fluids was followed by a decrease in the tidal volume and ventilation at pH 7.0, whereas at pH 7.6 an effect on respiration could not be observed. When CSP Ca++ was reduced to 30% of the reference concentration, an increase of respiratory parameters at pH 7.6 followed, while at pH 7.0 tidal volume and ventilation remained unchanged. Lower CSF Ca++ concentrations (0.15 meq/1) had no significant influence on respiration. Removal of Ca++ from the superfusing fluids caused respiratory irregularity which in some cases was accompanied by convulsions of skeletal muscles. Mean tidal volume and ventilation values were reduced. Effects of Ca++ removal were partially neutralized by adding equivalent amounts of Mg++ to the Ca++-free fluids, whereas Mg++ when added to fluids containing physiological amounts of Ca++, had no significant effect on respiration. The possible mechanisms involved in the propagation of Ca++ and Mg++ effects are discussed. © 1969.