Effect of Sustained Hydrostatic Pressure on Rat Bladder Smooth Muscle Cell Function

ObjectivesTo test a hypothesis that bladder smooth muscle cells (BSMCs) shift their phenotype from contractile to synthetic in response to elevated hydrostatic pressure. Although mechanical stimuli are needed for development of the bladder, the exact mechanisms for this process are poorly understood.MethodsRat BSMCs were exposed to 7.5 cm H2O of hydrostatic pressure in custom-made columns to a maximum of 48 hours. After exposure to pressure, the smooth muscle cells were fixed, stained, and imaged to quantify cell morphology and proliferation. Additionally, Western blotting was used to quantify extracellular signal-regulated kinase (ERK½) activation as well as phenotype marker proteins, α-smooth muscle actin, and SM-22.ResultsCompared with the control, BSMCs exposed to hydrostatic pressure exhibited a more spread morphology after 4 hours and the expression of activated ERK½ was a maximum of two-fold at 1.5-3 hours. Moreover, cell density of BSMCs exposed to hydrostatic pressure exhibited an increase after 48 hours when compared with their respective controls. In contrast, α-smooth muscle actin and SM-22 expression was similar in the control and in cells exposed to hydrostatic pressure for 48 hours.ConclusionsThe morphologic and proliferative changes of BSMC in response to hydrostatic pressure possibly indicate a phenotypic shift from contractile to synthetic. Moreover, the activation of ERK½ intracellular signaling pathway may represent a potential mechanism for the pressure-induced BSMC proliferation. The comparable levels of contractile proteins observed in both control and pressure group BSMCs suggest that not all the phenotype markers are regulated concomitantly by a single stimulus.