[Development of an in vitro cardiomyocytes cell model for embryotoxicological and pharmacological studies]

Permanent cell lines of pluripotent embryonic stem cells (ESC) are established from early embryonic stages (blastomeres of 8-cell embryos or blastocysts) of the mouse. We developed an in vitro system for differentiation which allowed the optimal development of ESC into spontaneously pulsating cardiomyocytes. The ESC-derived cardiomyocytes responded to cardioactive substances with heart-specific chronotropic reactions and modifications of the action potentials. The beta-adrenoceptor agonists (-)isoprenaline and clenbuterol, the mediators of the cAMP pathway forskolin and isobutylmethylxanthine as well as the alpha1-adrenoceptor agonist (-)phenylephrine caused positive chronotropic reactions. The muscarinic cholinoceptor agonist carbachol and the L-type Ca2+ channel blockers nisoldipine, diltiazem and gallopamil induced negative chronotropic effects. beta1-, alpha1-adrenoceptors and Ca2+ channels, but no beta2-adrenoceptors are involved in the chronotropic reaction of early developmental states of cardiomyocytes. Terminally differentiatied cardiomyocytes expressed beta2-adrenoceptors and displayed a positive chronotropic response to digitoxin. The contractions of spontaneously pulsating cardiomyocytes were concommitant with rhythmic action potentionals characteristic to those described for embryonic cardiomyocytes and sinusnode cells. The presented ESC-differentiation system may be useful for in vitro studies of cell differentiation and commitment. Furthermore, it may provide an alternative model for pharmacological investigations and for reproductive toxicology thus reducing animal use.