Feedback control of intracellular pH by means of iontophoretic H+/OH- injection

A new method for controlling intracellular PH (pH) within a single cell has been developed that is based on the iontophoretic injection of the pH-affe cting ions H+ and OH-. The H+/OH- injection currents are governed by an ele ctronic feedback system, which compares the actual pH(i), monitored by pH-s ensitive microelectrodes, with a command value. To avoid membrane potential (E-m) alterations caused by the H+/OH- currents, the pH(i) control is perf ormed under voltage-clamp conditions, using a two-electrode voltage-clamp d esign. This feedback-controlled iontophoretic injection system was capable of adjusting pH(i) between PH 6.8 and 8.0 with a precision of 0.031 +/-0.02 6 PH units (n=51) and without affecting E-m. We illustrate the application of this system by investigating the pH, dependence of glutamate receptors i n identified leech Retzius neurons. Stimulation of these receptors with the glutamatergic agonist kainate (50 muM) under control conditions induced an intracellular acidification of 0.14 +/-0.07 PH units (n=13). The feedback control system for pH(i) reduced this intracellular acidification to 0.02 /-0.01 PH units (n=15). The kainate-induced inward current was not affected by pH(i) alterations. This result demonstrates that the feedback system fo r pH(i) control was feasible for investigating the pH(i) dependence of phys iological processes and suggests that the glutamate receptors are not modul ated by pH(i).