The effects of sustained hydrostatic-pressure on select bladder smooth muscle cell functions

Purpose: Normal bladder development is believed to depend on the active work of the bladder for storing and expelling urine. When high urinary diversion is performed in infants and the bladder no longer undergoes normal filling, bladder development may be altered, ultimately resulting in bladder dysfunction. To help better understand this relationship of bladder function with growth at the cellular level we developed a novel laboratory method for applying hydrostatic pressure to cell cultures, and we characterized the response of neonatal bladder smooth muscle cells to physiological levels of sustained hydrostatic pressure. Materials and Methods: Neonatal ovine smooth muscle cells staining positive for desmin and alpha-smooth muscle actin were exposed to pressures of 0.3 (controls), 2, 4, 6 and 8.5 cm. water for 1, 3, 5 and 7 days. At the end of the experiments the cells were fixed, stained and counted. Mitogenic activity of the supernatant media from bladder smooth muscle cells exposed to 8.5 cm. water for 5 days (conditioned media) was tested before and after treatments of-heating, freezing, passing through a heparin-sepharose affinity chromatography column or after the addition of suramin, a nonspecific growth factor inhibitor. Statistical analysis was performed using Student's t test with p <0.05 considered. statistically significant. Results: Exposure of bladder smooth muscle cells to sustained hydrostatic pressures of 4, 6 and 8.5 cm. water resulted in increased cell proliferation. Differences became statistically significant (p <0.05)by day 5. Also, conditioned media contained mitogenic activity that was ablated by heating, freezing, passage through a. heparin-sepharose affinity chromatography column or with the addition of suramin. Conclusions: We have demonstrated a proliferative response of neonatal bladder smooth muscle after exposure to physiological levels of sustained hydrostatic pressure. This response is partially due to 1 or more transferable mitogenic factors. These data support the hypothesis that pressure associated with bladder filling is an important stimulus for detrusor development.