Effect of physical forces on bladder smooth muscle and urothelium

Abnormalities in bladder physiology may be due to obstruction (pressure) and/or neurological impairment. Clinically they can result in an increase in connective tissue and a decrease in bladder compliance. To study the effects of physical forces on the bladder without the influence of the nerves we developed a cellular model system by isolating the 2 major cell types in the bladder: smooth muscle and urothelial cells. Extracellular matrix protein biosynthesis by these 2 cell types in vitro has been characterized by metabolic labeling of proteins with [14C] radiolabeled proline and analysis by gel electrophoresis. These studies demonstrate that fetal bovine bladder smooth muscle and urothelial cells synthesize fibronectin and types I and III interstitial collagen. Since bladder cells exist in an active physical environment, we have attempted to simulate this at the cellular level. Using a device developed in our laboratory, we applied a precise and reproducible mechanical strain (physical force) to these 2 cell types. By enzyme linked immunosorbent assay we quantitated collagen types I and III and fibronectin synthesized by fetal bovine bladder smooth muscle and urothelial cells undergoing mechanical strain (4.9%). These cells were compared to unstrained control cells that were exposed to the same experimental conditions. For bladder smooth muscle cells we found a significant increase in collagen type III and fibronectin synthesis when compared to unstrained cells. In contrast, collagen type I synthesis decreased with mechanical strain. For bladder urothelial cells we found an increase in collagen type I and fibronectin while collagen type III remained unchanged. These studies demonstrate that extracellular matrix synthesis by urothelial and smooth muscle cells can be modulated by stretch (strain) in the absence of neurological input. It is likely that bladder function may be impaired as a result of abnormal synthesis of connective tissue.