Cyclic Stretch Promotes Proliferation and Contraction of Human Bladder Smooth Muscle Cells by Cajal-Mediated c-kit Expression in Interstitial Cells.

BACKGROUND The present study was performed to assess the effect of mechanical stretch on the proliferation and contractile function of hBSMCs. MATERIAL AND METHODS hBSMCs and ICCs were seeded at 8×104 cells/well in 6-well silicone elastomer-bottomed culture plates coated with type I collagen, and grown to 80% confluence in DMEM/10% FBS and a 5% CO₂ humidified atmosphere at 37°C. Cells of hBSMCs and hBSMCs/ICCs of co-culture were then subjected to continuous cycles of stretch-relaxation using a computer-driven, stretch-inducing device. The treated concentration of imatinib was 10 μM. Mechanisms underlying observed hBSMCs contraction were examined using Western blotting and RT-PCR. The 0.1 μM carbachol was separately added to the experimental groups, and 300 s was recorded by laser scanning confocal microscope. RESULTS We found that mechanical stretch increased contraction and proliferation of hBSMCs. Calcium ion activity increased significantly after mechanical stretch. The number of hBSMCs was significantly increased after the combination mechanical stretch with ICCs treatment. After combination mechanical stretch with hBSMCs/ICCs treatment, the mRNA and protein level of M2, M3, and c-kit were significantly increased. After combination of mechanical stretch with no imatinib treatment, the proliferation of hBSMCs was higher than others, and the mRNA and protein level of M2 and M3 were significantly increased. CONCLUSIONS We revealed that ICCs could promote hBSMC proliferation and contraction, and cyclic stretch could promote acetylcholine receptor M2 and M3 caused by c-kit in the ICCs, which promoted the contraction of hBSMCs.