GJA1 and breast carcinoma: To extend these observations and investigate the role of Cx43 gap junctions in breast cancer cells, we treated MCF7 cells with vehicle (water), a non-functional reverse peptide control (R-pep), or ACT1 and monitored for gap junctional activity using a Fluorescence Recovery After Photobleaching (FRAP)-based gap junction activity assay (gap-FRAP).