Effect of acetylcholine and adrenaline on ventricular action potentials of the human embryonic myocardium.

Using the glass microelectrode technique we measured the effect of adrenaline (ADR, 10(-5) mol . l-1) and acetylcholine (ACh, 10(-5) mol . l-1) on action potentials (AP) of the ventricular myocardium of 8- to 11-week-old human embryos. ACh prolonged the AP (by 20%), without affecting voltage of the plateau phase. ADR markedly elevated the plateau phase (by 8 mV) and prolonged the AP (by up to 40% of the initial duration). The ACh effect attained the maximum in 5-7 min and was frequency dependent. The ADR effect reached the maximum in 1-2 min. Neither ACh nor ADR affected the resting membrane potential value. The effect of ACh was blocked by atropine (10(-6) mol . l-1), showing that it is mediated by way of M-receptors. Propranolol (6.10(-6) mol . l-1) only partly blocked the effects of ADR. The results show that the human ventricular myocardium is already sensitive to the action of ACh and ADR before autonomic innervation of the heart develops.