Abstract
Tetrahymena pyriformis suspended in an inorganic medium accumulates3H-labelled taurine against a concentration gradient resulting in a cellular to extracellular taurine gradient of about 3 within 2 hours. This is observed in spite of the fact that taurine influx inTetrahymena via the saturable, Na1-dependent system and the leak pathway becomes gradually reduced with time after transfer to an inorganic, taurine free medium. Taurine is not accumulated byTetrahymena at pH below 7.0 or when protein synthesis is prevented by addition of cycloheximide. Addition of actinomycin D has no effect on the taurine accumulation. It is suggested that the transporter responsible for taurine accumulation inTetrahymena has a pH threshold of 7.0 and that translation but not transcription is conditional for the emergence of the transporter following transfer to inorganic medium. Taurine accumulation is reduced when the phosphatase inhibitor calyculin A is added at the initiation of starvation but unaffected when the inhibitor is added once the cells are in the inorganic medium. Addition of forskolin significantly enhances taurine accumulation. It is proposed that phosphorylation as well as dephosphorylation are involved in the regulation of taurine accumulation inTetrahymena pyriformis.
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