Determination of resting membrane potential of individual neuroblastoma cells (IMR-32) using a potentiometric dye (TMRM) and confocal microscopy.

The potentiometric dye, Tetramethylrhodamine methyl ester (TMRM) has been extensively used with fluorometry or optical microscopy to evaluate the electric potential across plasma or mitochondrial membranes. We present here a TMRM confocal microscopy-based potential measurement technique. Corrections are introduced to minimize nonspecific dye binding and insensitivity to low background levels. We have used this technique to compare the resting membrane potential of proliferating and differentiated human neuroblastoma cells (IMR-32).