Blocking Volume Regulated Anion Channels (VRAC) with DCPIB Depresses Avian Intrapulmonary Chemoreceptor (IPC) Discharge more in Tonic than Phasic Units

Intrapulmonary chemoreceptors (IPC) are respiratory vagal afferents that sense PCO 2 changes and are responsible for controlling breathing in birds. Volume regulated anion channels (VRAC) are responsible for volume regulation in a large variety of cell types. Small doses of DCPIB (1 to 8 μmol/kg), a specific blocker of VRAC, were used to test for VRAC presence in IPC of pentobarbital‐anesthetized ducks ( Anas platyrhyncos , n=11). Cycle triggered stimulus histograms of IPC action potential discharge to 0%–7% inspired CO 2 steps were recorded and separated into 2 groups according to their spike frequency adaptation: phasic (n=4), tonic (n=7). The IPC discharge for phasic units remained unchanged from the control for the 1 to 4 μmol/kg doses, while the 8 μmol/kg dose reduced the peak phasic adaptation (ANOVA, p<0.01). Tonic units progressively reduced discharge for all doses (ANOVA, p<0.01). Since DCPIB more strongly affects IPC discharge in tonic units compared to phasic units the results suggest that: 1. Tonic and phasic units may have different mechanisms for VRAC activation, or 2. Tonic units express more VRAC than phasic units. Support or Funding Information Support: NIH R15 HL087269‐02.