Use of ⁵¹Cr cell labelling to distinguish between release of radiolabelled amino acids from primary astrocyte cultures being due to efflux or cell damage

Continuous perfusion methods are widely used to monitor release of substances, particularly transmitters, from brain cell cultures growing as monolayers. However, if stimuli used to produce release also cause loss or lysis of cells, the appearance of label in the perfusate due to such effects will be indistinguishable from release. Using a perfusion method we have studied release of preloaded, radiolabelled amino acids from primary astrocyte cultures due to a variety of stimuli; hypotonic or high K⁺ media, activation of β-receptors or swelling-induced release due to isosmotic ethanol. In this study primary astrocyte cultures were simultaneously labelled with Na₂⁵¹CrO₄ and allowed to take up radiolabelled d-aspartate or taurine. It was found that while all of the above methods caused release of radiolabelled amino acids none caused release of ⁵¹Cr into the perfusion fluid. In contrast, perfusion with 0.05% (v/v) Triton X-100 did lead to release of ⁵¹Cr. Thus a variety of means of inducing swelling or shape changes in astrocytes causes true release of radiolabelled amino acids and simultaneously monitoring ⁵¹Cr release seems a convenient means of distinguishing such release from cell loss or lysis.