Alteration of cardiomyocyte gap-junctions and component
connexins (Cx) has been suggested to contribute to the development of
atrial fibrillation (AF), including postoperative AF. We tested different possible stimuli, such as
hypoxia and
ischemia, influencing
Cx43 and Cx40 expression and distribution in cultured atrial cells (HL-1) and reversibility of these processes after reoxygenation. Western-blot analysis and immunostaining using anti-Cx43, anti-Cx40 and anti-zonula occludens polyclonal
antibodies were performed. HL-1 cells exposed to
hypoxia for 24 and 48 h showed a reduction of
Cx43 protein levels by 75% and 90% respectively (p < 0.001). During reoxygenation following 24 h of
hypoxia,
Cx43 levels increased to reach the basal level within 48 h, while they remained at low level during reoxygenation following 48 h of
hypoxia. Furthermore, atrial cardiomyocytes subjected to simulated
ischemia (SI) were incubated in normoxic and hypoxic conditions for 3, 6, 9, 12 h. Atrial cardiomyocytes subjected to SI in addition to normoxia showed a progressive reduction of
Cx43 levels beginning from 3 h. During SI and
hypoxia, atrial
Cx43 levels showed an initial decrease after 3 h with a subsequent rescue beginning from 6 h of exposure (p = 0.001).
Hypoxia and
ischemia per se downregulate
Cx43 protein expression in atrial cardiomyocytes, but
protein downregulation is reversible, depending on
hypoxia duration and the association of the two triggers. These alterations characterize several conditions and might contribute to the generation of an arrhythmogenic substrate leading to AF onset and/or maintenance.