Coupling of receptors in brain membranes by fusion to the adenylate cyclase system of a foreign effector cell

Abstract

Receptor-effector coupling in the adenylate cyclase (AC) system was studied using fusion transfer of rat or monkey frontal cortex membranes to Friend erythroleukemia (Fc) cells. The indigenous AC activity of cortex membranes had previously been inactivated with N-ethylmaleimide. In the fusates, the AC activity could be stimulated through β-adrenoceptors using noradrenaline (NA), or through specific receptors fpor vasoactive intestinal polypeptide (VIP), or by fluoride which activates the effector components of the AC-system directly, bypassing receptors. There was a critical stoichiometric relationship between the receptor-stimulated cAMP output and the number of recipient cells of the fusion system, i.e. the total AC capacity as measured by fluoride stimulation. In fusates with rat brain membranes, the β-adrenoceptor coupling increased as the availability of recipient cells increased; on the other hand, the excess of recipient cells did not change the VIP receptor coupling capacity. In fusates with monkey brain membranes, the situation was the opposite: VIP receptor coupling increased as larger amounts of recipient cells were made available, but the β-adrenoceptor coupling capacity remained unchanged. The differences in coupling capacities were related to differences in receptor binding with higher β-adrenoceptor density in rat than in monkey frontal cortex membranes, as opposed to higher VIP receptor density in monkey than in rat frontal cortex membranes. Neuropeptide tyrosine (NPY) attenuated both NA-and VIP-induced activation of AC in the fusates; it was equally potent against both agents. In rat brain membrane fusates, the NA-induced AC activity was attenuated in a dose-dependent and apparently non-competitive manner. Pretreatment with pertussis toxin abolished the effect indicating that the NPY receptor couples to a mechanism involving G i and G o protein. In conclusion, the fusion procedure may allow the determination of the coupling capacity of receptors, activating or inhibiting adenylate cyclase.