Sodium Transport In the Brook Trout,Salvelinus fontinalis: Effects of Prolonged Low pH Exposure in the Presence and Absence of Aluminum

Abstract

This study examined the effects of prolonged exposure [Formula: see text] to low Ca2+(25 versus 400 μequiv/L), low pH (pH 5.2 versus 6.5) with and without Al (150 μg/L) on Na+uptake in adult brook trout (Salvelinus fontinalis). Na+uptake (JinNa+) was assessed by measuring radiotracer disappearance from the medium at ambient Na+(79 μequiv/L) and in response to acute increases in ambient Na+. The relationship between JinNa+and [Na+] was best described by a linear model with the slope of the line a measure of transport activity. Transport activity increased as a result of prolonged low Ca2+exposure at pH 6.5, but declined in fish maintained at pH 5.2. These fish showed no compensation in response to low pH; there was no recovery in transport activity when pH was acutely raised to 6.5, and lower pH's further inhibited uptake. In contrast, the Na+transport activity of fish maintained at pH 5.2 and 150 μg Al/L was significantly greater than that of fish acclimated to pH 5.2 alone and indeed greater than pH 6.5 controls. This indicates that Al exposure induced a compensatory mechanism in the gills that was not seen with low pH exposure alone.