A Rho-kinase inhibitor, Y-27632, reduces cholinergic contraction but not neurotransmitter release

This study examined the effects of the selective Rho-kinase inhibitor Y-27632 [(+)-(R)-trans-4-(1-aminoethyl)-(4-pyridyl)cyclohexanecarboxamide dihydrochloride]) on cholinergic nerve-mediated contraction and neurotransmitter release in murine and guinea-pig isolated tracheal preparations. In tracheal preparations obtained from both species, Y-27632 shifted carbachol concentration–effect curves to the right and reduced the maximal contractile response. Repeated electrical field stimulation (EFS) evoked transient, consistent and reproducible contractions in murine and guinea-pig tracheal preparations. Y-27632 inhibited these cholinergic nerve-mediated contractions in a concentration-dependent manner. EFS (0.1–30 Hz) elicited frequency-dependent cholinergic nerve-mediated contractile responses. In murine tracheal preparations, Y-27632 (3 μM and 10 μM) shifted frequency–response curves to EFS to the right by 5.5 and 13.0 fold respectively and markedly reduced the maximal contractile response. In murine and guinea-pig tracheal preparations loaded with [3H]-choline, Y-27632 (10 μM) significantly increased the EFS-induced outflow of radioactivity from airway cholinergic nerves by 27% and 54% respectively. Thus, Y-27632 inhibited both carbachol-induced and cholinergic nerve-mediated contractile responses. Conversely, Y-27632 increased neurotransmitter release from airway cholinergic nerves. However, since antagonism of acetylcholine-induced contraction by Y-27632 overwhelmed the increased neurotransmitter release, the overall effect of this Rho-kinase inhibitor was to inhibit cholinergic nerve-mediated contraction.