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Spike frequency adaptation in avian intrapulmonary chemoreceptors does not rely on Na+/H+ exchange (1092.9)

IPC are essential for avian breath‐by‐breath respiratory control and are inversely sensitive to lung PCO2. Evidence suggests IPC detect intracellular pH rather than molecular CO2, and that pHi reflects a dynamic interaction of intracellular CO2 hydration/dehydration, buffering, and transmembrane acid/base exchange. We used the Na+/H+ exchange (NHE) blocker dimethyl amiloride (DMA) to test NHE’s role in single‐unit IPC response to combined phasic and tonic CO2 step stimuli in anesthetized mallards (n=9). DMA depressed mean (tonic) IPC discharge response to CO2 step stimuli by 15%, 31%, 51%, and 58% at 1,3,8, and 13 µmol/kg, (p<0.05), but did not affect phasic discharge (spike frequency adaptation index, SFA). Depression of tonic CO2 response confirms earlier reports, and the new result that NHE has no effect on the phasic part of IPC step response demonstrates that other mechanisms must underlie SFA.