A study of steady state and kinetic regulation of chloride ion and osmotic pressure in hemolymph of oysters, Crassostrea virginica, exposed to tri-n-butyltin.

Two sets of experiments were made to determine if bis(tri-n-butyl)tin oxide (TBT) [IUPAC: hexabutyldistannoxane] influenced osmotic pressure or chloride ion concentration in hemolymph of adult American oysters, Crassostrea virginica. In the first set, oysters were acclimated to 5, 25 or 40%;, then exposed to bis(tri-n-butyl)tin oxide dissolved in seawater (0.5, 1.0 or 2.0 micrograms/L) for 11 days. Measurements of the total osmotic pressure and chloride ion concentration in hemolymph indicated that mean values of neither was significantly affected under steady state conditions. Oysters exposed to TBT exhibited a higher variation around the mean value for both total osmotic pressure and chloride ion concentration. There was significant mortality of oysters exposed to TBT in 25 and 40, but not in 5%. In a second experiment, adult oysters were acclimated to 25%, and simultaneously exposed to the TBT concentrations listed above for 10 days. Then, subgroups of oysters were abruptly moved to 5 or 40% and the time-course of adjustment of hemolymph osmotic pressure and chloride ion concentration was measured. During the first 25 hr, there was little adjustment to 5% in controls or TBT exposed oysters; apparently, they remained closed most or all of the time. In marked contrast, hemolymph of oysters moved to higher salinities rapidly readjusted. Exposure to TBT had a delaying effect on the schedule of the increase in hemolymph osmotic pressure and chloride ion concentration. Results of these experiments show that TBT has an indirect effect on osmotic pressure and chloride ion concentration adjustment in oysters; it does not appear to act strongly as an anionophore to influence anion transfer across epithelia.