Regulation of adrenoceptors and muscarinic receptors in the heart.

Receptor activation results in homologous regulation and can also affect other types of receptors (a process that has been reported to heterologous regulation). Heart cells express subtypes of muscarinic receptors and adrenoceptors, almost antagonistic in their action (M2 muscarinic receptors and beta1-adrenoceptors). Therefore, they provide an excellent model of heterologous regulation. Moreover, the minor subtypes of adrenoceptors and muscarinic receptors have been identified in the heart cells. The physiological significance of the minor subtypes is now under keen investigation and their function can be considered as complementary to the major subtypes. Taken together, it seems that the minor subtypes may play an important role in the receptor-heart function homeostasis and that heterologous regulation seems to exist in many heart receptor types and in the above mentioned pair of receptors.