The initial kinetics of NH3/NH4+ efflux from L3Teladorsagia circumcincta

The initial rate of NH3/NH4+ accumulation in a medium containing L3Teladorsagia circumcincta was 0.18–0.6pmolh−1larva−1, which increased linearly with larval density. However it appeared that the larva-generated external concentration of NH3/NH4+ did not exceed about 130μM. The rate of NH3/NH4+ accumulation increased with temperature between 4°C and 37°C, declined with increasing pH or increasing external NH3/NH4+ concentration and was not significantly affected by the concentration of the phosphate buffer or by exsheathing the larvae. We infer from these data that the efflux of NH3/NH4+ is a diffusive process and that the secreted or excreted NH3/NH4+ is generated enzymatically rather than dissociating from the surface of the nematode. The enzymatic source of the NH3/NH4+ is yet to be identified. Since the concentration of NH3/NH4+ in the rumen and abomasum is higher than 130μM, it is unlikely that T. circumcincta contributes to it, but NH3/NH4+ may be accumulated from the rumen fluid by the nematode. [Display omitted] ► The initial rate of NH3/NH4+ efflux from larvae was 0.18–0.6pmolh−1larva−1. ► The initial rate rose with temperature and fell at higher pH and external NH3/NH4+. ► The activation energy and permeability coefficient were estimated.