Adrenoceptor‐mediated changes of action potential and force of contraction in human isolated ventricular heart muscle

1 The effects of α‐adrenoceptor stimulation on the action potential and force of contraction were investigated in human isolated ventricular heart muscle and compared with those of β‐adrenoceptor Stimulation. 2 The maximal stimulation by isoprenaline of β‐adrenoceptors produced large changes in the force of contraction, which were accompanied by moderate increases in the height of the action potential. The maximal inotropic effect produced by stimulation of α‐adrenoceptors with phenylephrine, in the presence of propranolol (1 μmol l−1) was much smaller (about 10% of that seen in response to β‐adrenoceptor stimulation), and no significant changes of the action potential configuration were observed. 3 The effects of noradrenaline and adrenaline on the force of contraction were not affected by prazosin. 4 It is concluded that the adrenoceptor‐mediated changes of the force of contraction (in the presence of either noradrenaline or adrenaline) in the human ventricle are due virtually exclusively to the stimulation of β‐adrenoceptors.