Figure 3C showed that NP cells displayed a significantly higher (1.5-fold) basal level of c-fos promoter activity compared with AF cells (1.0-fold). The expression of c-fos in mature rat cells was studied using western blot analysis. Figure 3D showed that NP cells expressed a 62-kDa band, representing c-fos; expression was more prominent in the NP than in the AF. The gene discussed is FOS; the disease is atrial fibrillation.