Avian intrapulmonary chemoreceptor discharge rate is increased by anion exchange blocker ‘DIDS’

Avian intrapulmonary chemoreceptors (IPC) are neurons that sense lung P CO 2 and provide phasic feedback for the control of breathing in birds. To try to understand mechanisms of CO 2 transduction and intracellular pH regulation in IPC, the anion exchange inhibitor 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS) was used to block transmembrane Cl −/HCO 3 − transport. Single-unit IPC discharge rates were measured at steady intrapulmonary CO 2 levels and during step changes in CO 2 in 15 anesthetized, unidirectionally ventilated adult mallard ducks ( Anas platyrhynchos). Measurements were repeated after giving 50, 100 and 200 μmol/kg cumulative i.v. dosages of DIDS. Mean IPC discharge rates at steady (tonic) P CO 2 levels were significantly increased by 100 and 200 μmol/kg DIDS, but not by 50 μmol/kg DIDS. Mean dynamic (phasic) IPC responses to CO 2 steps were not significantly affected by DIDS. Results indicate that the DIDS-sensitive Cl −/HCO 3 − membrane exchanger is involved with tonic CO 2 signal transduction in IPC. However, because some individual IPC were unaffected by DIDS, yet still altered their discharge rate with CO 2, additional mechanisms besides the Cl −/HCO 3 − exchange are probably required for CO 2 chemotransduction in IPC.