Presence, distribution and physiological function of adrenergic and muscarinic receptor subtypes in the human heart

Abstract

The sympathetic and parasympathetic nervous system play a powerful role in controlling cardiac function by activating adrenergic and muscarinic receptors. In the human heart there exist α₁-, β₁- and β₂-adrenoceptors and M₂-muscarinic receptors and possibly also (prejunctional) α₂-adrenoceptors. β₁- and β₂-adrenoceptors are quite evenly distributed in the human heart while M₂-receptors are heterogeneously distributed (more receptors in atria than in ventricles). Stimulation of β₁- and β₂-adrenoceptors causes increases in heart rate and force of contraction while stimulation of M₂-receptors decreases heart rate (directly in atria) and force of contraction (indirectly in ventricles). Pathological situations (such as heart failure) or pharmacological interventions (for example, β-blocker treatment) can alter the distribution of β₁- and β₂-adrenoceptors in the human heart, while M₂-receptors are only marginally affected. On the other hand, relatively little is known on distribution and functional role of α₁- and α₂-adrenoceptor subtypes in the human heart.