The estrogen-responsive (MCF-7, ZR-75-1, MDA-MB-361) and estrogen non-responsive (MDA-MB-453, MDA-MB-435S, MDA-MB-468) human breast cancer cell lines were screened for the presence of the GIRK1 potassium channel by RT-PCR analysis. The gene discussed is KCNA3; the disease is breast cancer.