Dopamine-induced ionic currents in acutely dissociated rat neurons of CNS

Aim: To determine whether or not the dopamine (DA) can induce ionic current in single neuron acutely dissociated from different central areas including striatum, ventral tegmental area (VTA), substantia nigra pars compacta (SNC) and hippocampal CA₁ area. Methods: Using a new patch-clamp whole-cell recording technique, namely nystatin-perforated whole-cell configuration under voltage-clamp mode. Results: In 36 single neurons isolated from the striatum and VTA, DA 10-1000 μmol·L^-1 was quite diverse to elicit ionic current response. In 19 SNC neurons, 5 neurons (26%) response to 1 mmol·L^-1 DA represented as a small outward current (11.3 ± 2.4 pA) at a holding potential (V(H)) of -20 mV. In 25 of 69 (36%) examined hippocampal CA₁ pyramidal neurons, however, application of DA induced 3 types of current responses: outward current (8 neurons) accompanied with an increase of membrane conductance, slow inward current (5 neurons) with an decrease of membrane conductance and outward-following inward current (12 neurons) at a V(H) of -20mV. The concentration-response relationship of DA-induced currents showed the typical sigmoid shape with the threshold dose, being the maxium response dose are 3 μmol·L^-1 and 1 mmol·L^-1 respectively. The current-voltage (I-V) relationship of DA-induced responses did not show any voltage-dependent manner and the reversal potential (E(DA)) was close to the equilibrium potential of potassium (E(K)) calculated with the Nernst equation. TEA 5 mol·L^-1 effectively inhibited the DA-induced response. Conclusion: These results suggest that DA-induced outward current is carried by K⁺ in single hippocampal CA₁ pyramidal neuron.