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

Avian intrapulmonary chemoreceptors (IPC) are neurons that sense lung P-CO2 and provide phasic feedback for the control of breathing in birds. To try to understand mechanisms of CO2 transduction and intracellular pH regulatio n in IPC, the anion exchange inhibitor 4,4'-diisothiocyanostilbene-2,2'-dis ulfonic acid (DIDS) was used to block transmembrane Cl/HCO3- transport. Sin gle-unit IPC discharge rates were measured at steady intrapulmonary CO, lev els and during step changes in CO2 in 15 anesthetized, unidirectionally ven tilated adult mallard ducks (Anas platyrhynchos). Measurements were repeate d after giving 50, 100 and 200 mu mol/kg cumulative i.v. dosages of DIDS. M ean IPC discharge rates at steady (tonic) P-CO2 levels were significantly i ncreased by 100 and 200 mu mol/kg DIDS. but not by 50 mu mol/kg DIDS. Mean dynamic (phasic) TPC responses to CO, steps were not significantly affected by DIDS. Results indicate that the DIDS-sensitive Cl-/HCO3- membrane excha nger is involved with tonic CO, signal transduction in IPC. However, becaus e some individual IPC were unaffected by DIDS. yet still altered their disc harge rate with CO, additional mechanisms besides the Cl-/HCO3- exchange ar e probably required for CO2 chemotransduction in IPC. (C) 2001 Elsevier Sci ence B.V. All rights reserved.