Isoproterenol selectively releases endogenous and [ 14 C]‐labelled taurine from a single cytosolic compartment in astroglial cells

Taurine is stored in and released from astroglial cells. We have investigated whether taurine is stored in multiple subcellular compartments and whether taurine is released from a distinct pool. Taurine compartmentation was examined by determining the subcellular distribution of labelled taurine and by comparing the specific radioactivities of taurine in cells with that of the taurine released into the superfusion medium during receptor stimulation. Three observations indicate that taurine is found in a single subcellular pool. First, labelled taurine was localized exclusively within a freely exchangeable pool and not sequestered in membrane‐bound compartments. Second, endogenous and newly acquired [ 14 C]taurine was released identically by the β‐adrenergic agonist isoproterenol (IPR). Third, measurements of the specific radioactivity of taurine indicate that accumulated [ 14 C]taurine mixes homogeneously with endogenous taurine and both are simultaneously released from the same pool. Chemical analysis revealed net uptake of taurine from the medium during loading and a net loss during IPR‐stimulated release. Taurine was selectively released by IPR; five other amino acids found in the superfusion medium were unaffected. One possible mechanism capable of explaining these results is that receptor‐mediated taurine release from astroglia occurs by a selective transporter moving taurine from a single cytoplasmic pool to the extracellular space.