Simultaneous tracer transfer and double whole-cell recording between HeLa–Cx47-EGFP cells. A, Illustration of Lucifer yellow transfer between a single cell pair. Lucifer yellow was loaded into one of the cells (cell 1) through the patch pipette. The two panels show (from left to right) a phase-contrast image illustrating the positions of patch pipettes (left pipette was loaded with Lucifer yellow) and a fluorescence image taken with a filter set for Lucifer yellow 4 min after establishing whole-cell recording in cell 1. After establishing a whole-cell recording in cell 2, g_j was determined to be 12 nS. B, Illustration of DAPI transfer between an electrically coupled cell pair. The twopanels are as described in A except that the fluorescence image for DAPI was obtained 10 min after establishing whole-cell recording in cell 1 and a filter set for DAPI was used.g_j was measured to be 40 nS. DAPI preferentially labeled the nuclei of both cells.