The Rho kinase (ROCK) inhibitor Y-27632 reduces the β₂-adrenoceptor density but enhance cAMP formation in primary...

The present study addresses the effect of the Rho-kinase (ROCK) inhibitor Y-27632 on the β₂-adrenoceptor density and β-agonist-stimulated intracellular second messenger cAMP formation in primary equine bronchial epithelial cells (EBEC). Y-27632 significantly decreased the β₂-adrenoceptor number (B_max) without markedly affecting the receptor affinity (dissociation constant, K_D) to the radioligand [¹²⁵I]-iodocyanopindolol (ICYP). In contrast, Y-27632 augmented the β-agonist-stimulated intracellular cAMP production. Herein, Y-27632 markedly increased the maximal cAMP responses (E_max) (isoproterenol > epinephrine > norepinephrine) but did not shift the β-agonist concentration-effect curves to the left. The β₂-selective antagonist ICI 118.551 and the β_1/β₂-antagonsit propranolol but not the β₁-selctive antagonist CGP 20712A reversed the isoproterenol-induced cAMP formation equally in Y-27632-treated and control EBEC, suggesting the effect was merely related to the β₂-subtype. These results show that Y-27632 differentially regulates the receptor density and function. Thus, these findings provide the first evidence that the functional interaction of the β₂-adrenoceptor and Rho-kinase (ROCK) signaling pathways decreases the receptor expression but enhances receptor downstream cAMP formation. This differential regulation of the receptor density and function by Y-27632 should be further reconsidered with regard to the beneficial effect of the drug in asthma therapy.