The effects of silver on intestinal ion and acid-base regulation in the marine teleost fish, Papophrys vetulus

Exposure to elevated silver (as AgNO3) concentrations (6-9 mu M) in seawate r was associated with comparably high silver concentrations in the intestin al fluids of the lemon sole (Parophrys vetulus), and a tendency for reduced drinking rate. The effects of silver on intestinal ion and acid-base regul ation were studied using in situ perfusion of the intestine. Intestinal net Cl- uptake was reduced from 0.4 to 0.1 and intestinal net Na+ uptake from 0.2 to 0 mmol kg(-1) h(-1) during silver exposure (9 mu M). At the same lim e, intestinal HCO3- net efflux was reduced from 0.2 to 0.1 mmol kg(-1) h(-1 ). Both intestinal Na+ and Cl- uptake and Cl-/HCO3- exchange are thus sensi tive to silver, but to different extents. None of the observed effects were reversible during 24 h of recovery. Intestinal water transport was highly variable in vivo in the perfused preparation, and no significant effect of silver exposure was observed. However, in vitro intestine preparations exhi bited reduction of intestinal net water flux from 4 to 1 mu l cm(-2) h(-1) during silver exposure together with reduced unidirectional Cl- influx. Red uced water intake and transepithelial water transport in silver-exposed fis h resulted in moderate hemoconcentration evident from higher hematocrit val ues, but not in increased plasma ion levels. The latter could reflect a com pensatory response via increased branchial Na+/K+-ATPase levels, observed i n silver-exposed fish, indicative of increased branchial ion transport capa city. Impairment of intestinal ion and water transport as a result of silve r intake via drinking could be an important part of the fatal cascade of ph ysiological effects observed in marine fish during acute silver exposure. ( C) 1999 Elsevier Science Inc. All rights reserved.