Efficient transfection of NG108-15 cells with GABA B receptor subunits was achieved using polyethylenimine. Baclofen modulated high voltage-activated Ca 2 + current in differentiated cells transfected with GABA B 1 and GABA B 2 receptor subunits or with the GABA B 2 subunit alone, but not with the GABA B 1 subunit alone. Characteristics of the current modulation were very similar for cells transfected with GABA B 1 / 2 and GABA B 2 subunits. Using antisense oligonucleotides against GABA B 1 subunits and also western immunoblotting, we are able to show that NG108-15 cells contain endogenous GABA B 1 subunits. Therefore, functional receptors can be formed by the combination of native GABA B 1 subunits with transfected GABA B 2 subunits, in agreement with the proposed heteromeric structure of GABA B receptors. Finally, we used selective channel blockers to identify the subtypes of Ca 2 + channels that are modulated by GABA B receptors. In fact, in differentiated NG108-15 cells, the recombinant GABA B receptors couple only to N-type Ca 2 + channels.