Characterization of cultured bladder smooth muscle cells: Assessment of in vitro contractility

Purpose: The contractile properties of in vitro cultured bladder smooth muscle cells (SMC) are unknown. This study characterized the in vitro contractile response of human and rat bladder SMC to several pharmacological agonists known to induce in vivo contraction of intact bladder muscle. Materials and Methods: Human and rat bladder SMC were seeded separately within attached collagen lattices. Contractility of SMC was analyzed by measuring alterations in lattice diameter after exposure and release to the following contractile agonists: carbachol (10(-7) - 10(-3) M), calcium-ionophore (10 mu M), lysophosphatidic acid (LPA) (1 mu M), endothelin (0.1 mu M), KCl (3.33 mM) angiotensin II (10 mu M), and serotonin (100 mu M). Results were recorded as a mean reduction of the lattice diameter. In addition, immunohistochemical analysis for phenotypic markers of smooth muscle cell differentiation was performed on bladder SMC cultured within collagen lattices. Human palmar fascia fibroblasts, which have been previously well characterized by in vitro contractility and immunohistochemistry, were tested in parallel and used as controls for all the above experiments. Results: Human SMC had significant contractile responses to calcium-ionophore (31% +/- 4 relative percent contraction, p <0.05), LPA (34% +/- 4, p <0.05), and endothelin (37 +/- 5%, p <05). There was no significant contraction in response to carbachol, angiotensin II, KCI, or serotonin. Rat bladder SMC had a similar contractile response but did not contract in response to endothelin. In contrast to human and rat bladder SMC, fibroblasts did not contract to calcium-ionophore. Conclusions: In vitro cultured bladder SMC demonstrate loss of contractile response to normal in vivo pharmacologic agonists. Both human and rat bladder SMC can be distinguished in vitro from fibroblasts based upon their lack of contractile response to calcium-ionophore. These results demonstrate the ability to further characterize cultured bladder SMC with in vitro contractility. Further characterization is essential if we are to advance our understanding of the clinical applicability of in vitro studies utilizing cultured bladder SMC.