Extracellular carbonic anhydrase and an acid-base disequilibrium in the blood of the dogfish Squalus acanthias

摘要: The electrometric [Delta]pH method and an in vitro radioisotopic HCO3- dehydration assay were used to demonstrate the presence of true extracellular carbonic anhydrase (CA) activity blood Pacific spiny dogfish Squalus acanthias. An extracorporeal circulation stopflow technique then characterise acid­base disequilibrium arterial (postbranchial) blood. During period, pH (pHa) decreased by 0.028±0.003 units (mean ± s.e.m., N=27), contrast increase pHa 0.029±0.006 N=6) observed seawater-acclimated rainbow trout Oncorhynchus mykiss under similar conditions. negative was abolished addition bovine CA circulation, while inhibition benzolamide gill membrane-bound activities reversed direction such that increased 0.059±0.016 during period. When red cells (rbcs) additionally inhibited using acetazolamide, magnitude significantly -0.045±0.007 N=6). Blockage rbc Cl-/HCO3- exchanger 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS) also disequilibrium, this case -0.089±0.008 Exposure hypercapnia had no effect on whereas larger hypoxic conditions, at -0.049±0.008 results are interpreted within a framework which absence positive CO2 excretion is attributed activities. may arise from continuation exchange postbranchial and/or hydration added plasma postbranchially. Two possible sources discussed; production or admixture having 'low' 'high' tensions, i.e. mixing with has bypassed respiratory surface.