Amiloride (10(-3) M), a Na+-H+ countertransport inhibitor, infused into the cisterna magna (10 microliter/min for 40 min) of
ketamine-
xylazine-anesthetized rabbits decreased the cerebrospinal fluid (CSF) HCO3- response to 3 h of
hypercapnia [arterial PCO2 (PaCO2) = 60 Torr] by 21.6% (mean delta CSF [HCO3-]/delta PaCO2 0.232 vs. 0.296 mmol.l-1.Torr-1, P less than 0.05).
Diethyl pyrocarbonate (DEPC, 10(-3) M), a
histidine-blocking agent, infused into the cisterna magna decreased the CSF HCO3- response to
hypercapnia by 25.3% (mean delta CSF [HCO3-]/delta PaCO2, 0.230 vs. 0.308 mmol.l-1.Torr-1, P less than 0.02). DEPC is known to inhibit the ventilatory response to
hypercapnia (E. Nattie. Respir. Physiol. 64: 161-176, 1986) by a direct effect at the ventrolateral medulla (E. Nattie. J. Appl. Physiol. 61: 843-850, 1986). In this study
amiloride had no significant effect on the ventilatory response to
hypercapnia. The interpretation is that a Na+-H+ countertransport
protein, perhaps with a
histidine at a key location, is involved in CSF
acid-base regulation and that
amiloride appears to have no effects on the chemoreception process. DEPC appears to have effects on chemoreception and on CSF
acid-base regulation.