Effects of cyclosporin A on contractile activity and cytoskeleton in chickembryo cardiomyocytes

The effects of cyclosporin A (CsA), a clinically used immunosupressive drug , on contractile activity of chick cardiomyocytes grown as small aggregates or explants suspended on a network of elastic glass fibres or cultured in a monolayer were analysed in vitro with computer-aided image cytometry meth ods. At therapeutic concentrations (200-1500 ng/mL), CsA induced changes in the frequency and amplitude of the beating activity of cardiomyocytes 15 m in after application. Longer treatment of cardiomyocytes, for 20-24 h, addi tionally induced changes in their shape and cytoskeleton organization (F-ac tin and alpha-actinin distribution). These results indicate that CsA is abl e to affect directly the contractile activity, morphology, and cytoskeleton architecture of heart cells.