I have some questions.
What s the end goal of your experiment?
Which transporter are you studying?
This will affect which ions are co transported with the substrate and what kind of current you will see.
If you are studying a SCL6 transporter (Dopamine, GABA, Serotonin, Norepinephrine) you can inject the mRNA for the transporter into the oocytes, then record from them a couple of days later.
During recording, voltage clamp your cell at about -60 mV to -80mV and then perfuse in the substrate for your transporter (e.g. GABA or dopamine). You should record an inward current.
Private message/email me if you need more help.