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DOI: 10.1055/s-0034-1367452
How do cardiomyocytes sense stretch? Effects of cyclic mechanical stretch on cardiomyocyte cellular organization
Objectives: We wanted to find out how cardiomyocytes sense stretch and how stretch affects cytoskeleal organization.
Methods: Neonatal rat cardiomyocytes cultured on felxible membranes, were subjected to cyclic mechanical stretch (1 Hz, 10% eliongation) for 24 h, either as circular or as longitudinal stretch, using the FlexCell stretch system. Cells were treated either with vehicle, the focal adhesion kinase (FAK) inhibitor PF-573,228 (100 nM), or the stretch-activated ion channel blocker gadolinium (Gd3+; 10 µM).
Results: Cyclic mechanical stretch induced elongation of the cardiomyocytes together with accentuation of Cx43 at the cell poles, and with an orientation of the cell axis transverse to the radial stretch, or -in other words- near to the circumferential stretch axis. Moreover, stretch resulted in ca. 1.4 fold increased Cx43 expression. FAK was found to be phopshorylated at the edges of the cells. In order to find out, how cardiomyocytes might sense stretch, we first investigated a possible effect of Gd3+. It became obvious that Gd3+ had no effect on elongation or polarization and did not affect stretch-induced Cx43 expression. Next, we tested a possible influence of the FAK-inhibitor on the stretch -induced changes. Interestingly, the FAK inhibitor antagonized completely the stretch-induced elongation, orientation and Cx43-polarization. However, the stretch-induced Cx43 expression was insensitive to this treatment.
In order to clarify the finding that the cells in circular stretch did not exactly organize either transverse or longitudinal to the stretch axis, we decided to use a longitudinal stretch protocol. In longitudinally stretched cells, we found that the cardiomyocytes also showed elongation, Cx43 polarization, and orientation near to the stretch axis, but -as in circular stretch- not exactly in the stretch axis but ca. 25° to it.
This means that this directed stretch gives the cell a vector of force. In order to test whether this leads to an orientation, we investigated the tubular system, the Golgi apparatus, the SR and the nucleus. We found that the microtubules orientated near to the stretch axis (i.e. in longitudinal cell axis), the Golgi moved towards the vertex of the stretch angle, while the nucleus moved towards the rear of the cell. The plus motor protein kinesin accentuated at the cell poles.
Conclusions: Stretch is sensed via FAK and leads to intracellular re-organization and orientation.