Relations between β-adrenoceptor occupancy and increases of contractile force and adenylate cyclase activity induced by catecholamines in human ventricular myocardium
In conclusion, our data indicate that exposure of 1321N1 astrocytoma cells to catecholamines initiates a series of reactions that decreases cellular responsiveness to catecholamines and eventually results in a loss of functional beta AR from the cell. Whether the series of reactions depicted in Fig. 1 indeed represents a sequential process is not yet known. The molecular nature of the beta AR modifications responsible for uncoupling, internalization, and loss of binding also remains unknown. Nonetheless, these reactions are not restricted to the beta AR/AC system of 1321N1 astrocytoma or C62B glioma cells, since a number of investigators working with a variety of homogeneous cell systems have reported the occurrence of similar phenomena (2,7,8,13-16,19,21,28). Thus, the basic framework of catecholamine-induced modification of the properties of beta AR in astrocytoma cells is likely representative of the general phenomenon of agonist-specific desensitization of the beta AR-linked AC of mammalian cells.