Differential respiratory effects of HCO3- and CO2 applied on ventral medullary surface of rats.
To estimate whether H+ is the unique stimulus of the medullary chemosensor, ventilatory effects of HCO3- and/or CO2 applied on the ventral medullary surface using an improved superfusion technique and of CO2 inhalation were compared in halothane-anesthetized spontaneously breathing rats. Superfusion with low [HCO3-]-acid mock cerebrospinal fluid (CSF) (normal Pco2) induced a significant increase in ventilation, with an accompanying reduction in endtidal Pco2 (PETco2). High [HCO3-]-alkaline CSF depressed ventilation. Changes in Pco2 of superfusing CSF, on the other hand, had no significant effect despite the similar changes in pH. Simultaneous decrease in [HCO3-] and Pco2 of mock CSF with normal pH also maintained stimulated respiration. CO2 inhalation during superfusion with various [HCO3-] solutions caused further increase in ventilation as PETco2 increased. The results suggest that the surface area of the rat ventral medulla contains HCO3- (or H+)-sensitive respiratory neural substrates which are, however, little affected by CO2 in the subarachnoid fluid. A CO2 (or CO2-induced H+)-sensitive chemosensor responsible for the increase in ventilation during CO2 inhalation may exist elsewhere functionally apart from the HCO3- (or H+)-sensitive sensor in the examined surface area.
Tojima
H
H
Department of Chest Medicine and Physiology II, School of Medicine, Chiba University, Japan.
Kuriyama
T
T
Fukuda
Y
Y
D000818:Animals; D001639:Bicarbonates / Q000008:administration & dosage* / Q000134:cerebrospinal fluid; D002245:Carbon Dioxide / Q000008:administration & dosage* / Q000134:cerebrospinal fluid; D002628:Chemoreceptor Cells / Q000187:drug effects / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012119:Respiration / Q000187:drug effects* / Q000502:physiology
D001639:Bicarbonates; D002245:Carbon Dioxide