Because the glutamate transporter of Müller cells is electrogenic, its function can be assessed by electrophysiological methods. In this study, the perforated-patch configuration of the patch–clamp technique was used to monitor the currents of isolated rat Müller cells. An advantage of the perforated-patch configuration is that it minimizes the disruption of the recorded cell’s cytoplasm and, consequently, the loss of intracellular regulatory molecules that may influence the functioning of the glutamate transporter. However, because a recording pipette detects currents generated by the activity of ion channels, as well as electrogenic transporters, we strove to minimize changes in ion channel activity during activation of transporter activity. To help in this, barium was included in the perfusate to block K
IR channels, which are inhibited when Müller cells are exposed to glutamate.
37 38 However, in Müller cells, glutamate also inhibits a barium-resistant outward current that is activated at voltages depolarized to approximately −50 mV.
39 For this reason in a number of experiments, we used PDC, which is a selective ligand for the glutamate transporter.
40 Because PDC potently binds to glutamate transporters
40 as it is taken up into cells,
41 this molecule is often used to prevent the transport of glutamate by GLAST. In our study, use of PDC permitted activation of the Müller cell glutamate transporter over a wide range of voltages without significant changes in ion channel activity.