Release of preloaded taurine and hypotaurine from astrocytes in primary culture: stimulation by calcium-free media.

The spontaneous and stimulated release of taurine and hypotaurine from astrocytes in primary cultures were investigated. Spontaneous efflux was slow, less than one half of preloaded labeled taurine and hypotaurine still remaining in the cells after a 60-min efflux period. The release processes of both amino acids were in principle similar. No homo- or heteroexchange with extracellularly added taurine, hypotaurine or GABA could be detected, and depolarizing potassium concentrations failed to stimulate taurine or hypotaurine release. On the other hand, omission of calcium ions from medium increased efflux of taurine and hypotaurine about three- and twofold, respectively, in both high-K+ and normal-K+ media.