Taurine and glycine activate the same Cl- conductance in substantia nigra dopamine neurones

Intracellular recordings were made from substantia nigra dopamine neurones in a rat brain slice preparation. Spontaneous firing in these cells was reversibly inhibited by taurine applied by superfusion (300 microM-20 mM) or by focal pressure ejection. Neurones recorded with electrodes filled with KCl were depolarised at resting potential by taurine; the taurine depolarisation reversed polarity at -36.6 +/- 1.0 mV (7 cells). When electrodes filled with K-acetate or K-methyl sulphate were used, taurine caused a hyperpolarisation which reversed at -74.2 +/- 3.8 mV (9 cells). These effects of taurine were accompanied by a fall in input resistance or, in voltage clamp, an increase in conductance. Taurine thus appeared to increase membrane chloride conductance. The effect of taurine persisted in tetrodotoxin, 0-Ca2+/10 mM Mg2+, and bicuculline, but was blocked by strychnine (10 microM). Maximal responses to either taurine or glycine occluded responses to the other amino acid. Taurine therefore acts directly on dopamine neurones in the substantia nigra to increase the same membrane Cl- conductance as that mediating the action of glycine. Taurine may also act at the same recognition site as glycine in these cells.