Ventilatory sensitivity to ammonia in the Pacific hagfish (Eptatretus stoutii), a representative of the oldest extant connection to the ancestral vertebrates [RESEARCH ARTICLE]

Junho Eom, Marina Giacomin, Alexander M. Clifford, Greg G. Goss, and Chris M. Wood Ventilatory sensitivity to ammonia occurs in teleosts, elasmobranchs, and mammals. Here we investigated whether the response is present in hagfish. Ventilatory parameters (nostril flow, pressure amplitude, velar frequency, and ventilatory index, the latter representing the product of pressure amplitude times frequency), together with blood and water chemistry, were measured in hagfish exposed to either high environmental ammonia (HEA) in the external sea water or internal ammonia loading by intra-vascular injection. HEA exposure (10 mM NH4HCO3 or 10 mM NH4Cl) caused a persistent hyperventilation by 3 h, but further detailed analysis of the NH4HCO3 response showed that initially (within 5 min) there was a marked decrease in ventilation (80% reduction in ventilatory index and nostril flow), followed by a later 3-fold increase, by which time plasma total ammonia concentration had increased 11-fold. Thus, hyperventilation in HEA appeared to be an indirect response to internal ammonia elevation, rather than a direct response to external ammonia. HEA-mediated increases in oxygen consumption also occurred. Responses to NH4HCO3 were greater than those to NH4Cl, reflecting greater increases over time in water pH and PNH3 in the former. Hagfish also exhibited hyperventilation in response to direct injections of isotonic NH4HCO3 or NH4Cl solutions into the caudal sinus. In all cases where hyperventilation...
Source: Journal of Experimental Biology - Category: Biology Authors: Tags: RESEARCH ARTICLE Source Type: research