Question: 

Cyclic mechanical stretch (CMS) and angiotensin-II (AT) play an important role in cardiac remodelling. Thus, we examined how CMS and AT affect localization and expression of the gap junction protein connexin43 (Cx43).

Methods: 

Neonatal rat cardiomyocytes cultured on gelatine coated FlexCell cell culture plates were kept static or were exposed to cyclic mechanical stretch (110% of resting length, 1Hz) for 24hours without or with additional AT (0.1mmol/L). Moreover, inhibitors of AT-receptors (AT-R) were used (for AT-R1: losartan 0.1mmol/L, for AT-R2: PD123177 0.1mmol/L). Thereafter, the cardiomyocytes were investigated by immunocytochemistry, PCR and Western blot.

Results: 

After 24hours of CMS cardiomyocytes were significantly elongated and orientated 75±1.6° perpendicular to the stretch axis. Furthermore, CMS significantly accentuated Cx43 at the cell poles (ratio Cx43 polar/lateral static: 2.32±0.17; CMS: 10.08±3.2). Additional AT application significantly reduced Cx43 polarisation (ratio Cx43 polar/lateral AT: 4.61±0.42). The combined administration of AT and losartan to CMS further reduced Cx43 polarisation to control levels while the AT-R2 blocker PD123177 restored polarisation. Moreover, CMS and AT application resulted in a significant Cx43-protein and Cx43-mRNA up-regulation which could be blocked by losartan but not by PD123177.

Conclusions: 

CMS results in a self-organisation of the cardiomyocytes leading to elongated cells orientated transverse towards the stretch axis with enhanced Cx43 expression and Cx43-accentuation at the cell poles. AT enhances total Cx43-mRNA and -protein expression probably via AT-R1 (=inhibitory effect of losartan) and reduces Cx43 polarisation presumably via AT-R2, since PD123177 restored the negative effects of AT.