Objective. To investigate the characteristics of urotensin II （U II） receptor in the rat airway smooth muscle and the effect and signal transduction pathway of U II on the proliferation of airway smooth muscle cells. Methods. Using 125I UII binding assay to measure the Bmax and Kd of U II receptor. Using the 3H TdR incorporation to determine the effect of U II on the proliferation of airway smooth muscle cells and its signal transduction pathway. Using Fura 2/AM to measure the effect of U II on the cytosolic free calcium concentration. Results. 1. 125I UII binding increased with the time and reached saturation at 45min. The Bmax was （11.36±0.37）fmol/mg pr and Kd was （4.46±0.61）nmol/L. 2. U II increased 3H TdR incorporation of the airway smooth muscle cells in a dose dependent manner. 3. H7

PD98059 and nicardipine

inhibitors of PKC

MAPK

calcium channel

respectively

significantly inhibited U II stimulated 3H TdR incorporation of airway smooth muscle cells. W7

inhibitor of CaM PK

had no effect. 4. Cyclosporin A

inhibitor of CaN

inhibited 3H TdR incorporation of the airway smooth muscle cells induced by U II in a dose dependent manner. 5. U II promoted cytosolic free calcium concentration increase by 18%. Conclusions. 1. There was U II receptor in the rat airway smooth muscle. 2. The effect of U II stimulated 3H TdR incorporation of airway smooth muscle cells was mediated by such signal transduction pathway as Ca2+

PKC

MAPK and CaN

etc.