Receptor crosstalk protein, calcyon, regulates affinity state of dopamine D1 receptors

The recently cloned protein, calcyon, potentiates crosstalk between G(s)-co upled dopamine D1 receptors and heterologous G(q/11)-coupled receptors allo wing doparnine D1 receptors to stimulate intracellular Ca2+ release, in add ition to cAMP production. This crosstalk also requires the participating G( q/11)-coupled receptors to be primed by their agonists. We examined the abi lity of calcyon and priming to regulate the affinity of dopamine DI recepto rs for its ligands. Receptor binding assays were performed on HEK293 cell m embrane preparations expressing dopamine DI receptors either alone or in co mbination with calcyon. Co-expression of dopamine DI receptor and calcyon a ffected neither the affinity of this receptor for antagonists nor the affin ity of agonist binding to this receptor high and low-affinity states. Howev er, the presence of calcyon dramatically decreased the proportion of the hi gh-affinity doparnine DI receptor agonist binding sites. This decrease was reversed by carbachol, which primes the receptor crosstalk by stimulating e ndogenous G(q/11)-coupled muscarinic receptors. Our findings suggest that c alcyon regulates the ability of doparnine DI receptors to achieve the high- affinity state for agonists, in a manner that depends on priming of recepto r crosstalk. (C) 2001 Elsevier Science B.V. All rights reserved.