Cyclic mechanical stretch induces cardiomyocyte orientation and polarization of the gap junction protein connexin43.

RATIONALE: Cyclic mechanical stretch (CMS) is an important physiological and pathological factor in the heart.
OBJECTIVE: We examined whether CMS can affect localization of gap junctions with regard to the cell axis. METHODS AND
RESULTS: Neonatal rat cardiomyocytes were cultured (7 days) on flexible 6-well plates. Thereafter, cells were kept static or stimulated with CMS (1 Hz; 0, 10, 20% elongation) for 0, 24, or 48 hours (with or without 10 micromol/L PD98059, 5 micromol/L BIM I (bisindolylmaleimide I), 2 micromol/L H8 [N-(2-methlyamino-ethyl)-5-isoquinoline-sulfonamid], or 0.1 micromol/L angiotensin II. Additionally, cells were exposed to 24 hours of CMS followed by 24 hours of static recovery. CMS (24 hour, 10%) induced elongation of the cardiomyocytes and orientation 79+/-8 degrees toward the stretch direction. Moreover, the distribution of connexin (Cx)43 together with N-cadherin changed, so that both proteins were accentuated at the cell poles, whereas in nonstretched cells, they were distributed around the cell without preferential localization. Additional angiotensin II reduced polar Cx43 accentuation. The CMS-induced changes in Cx43 were reversible within 24 hours after end of stretch, and could be completely prevented by the MEK1/2 inhibitor PD98059 but not by BIM I or H8. Moreover, stretch resulted in Cx43 protein and Cx43-mRNA upregulation and in a significant upregulation of the phosphorylated forms of ERK1/2, glycogen synthase kinase 3beta and AKT. Furthermore, CMS resulted in a significant increase of the transcription factors activator protein 1 and CREB (cAMP response element-binding protein) in the nucleus.
CONCLUSIONS: CMS results in self-organization of cardiomyocytes leading to elongated cells orientated transverse to the stretch axis, enhanced Cx43 expression and Cx43 accentuation at the cell poles. The Cx43-changes seem to depend on the ERK1/2 signaling cascade.