Corticotropin-releasing factor receptors induce calcium mobilization through cross-talk with Gq-coupled receptors

The cross-talk between corticotropin-releasing factor (CRF) and muscarinic receptors was investigated by measuring evoked transient increases in cytosolic calcium concentration. HEK293 cells stably expressing human CRF type 1 (hCRF1) and type 2(a) (hCRF2(a)) receptors were stimulated with the muscarinic receptor agonist carbachol and shortly after by a CRF agonist. Unexpectedly, this second response was enhanced when compared to stimulating naive cells either with carbachol or CRF agonist only. Priming with 100 μM carbachol increased the maximal CRF agonist response and shifted its concentration–response curve to the left to attain almost the same potency as for stimulating the production of the natural second messenger cyclic AMP. Yet, priming did not affect CRF agonist-stimulated cyclic AMP production itself.Carbachol priming was not restricted to recombinant CRF receptors only since endogenously expressed β2-adrenoceptors also started to produce a robust calcium signal. Without priming no such signal was observed. Similar findings were made in the human retinoblastoma cell line Y79 for endogenously expressed CRF1 receptors and the type 1 pituitary adenylate cyclase-activating polypeptide receptors but not for the CRF2(a) receptors. This differentiation between CRF1 and CRF2 receptors was further supported by use of selective agonists and antagonists. The results suggest that stimulating a Gq-coupled receptor shortly before stimulating a Gs-coupled receptor may result in a parallel signaling event on top of the classical cyclic AMP pathway.