The umbrella cells that line the bladder are mechanosensitive, and bladder filling increases the apical surface area of these cells; however, the upstream signals that regulate this process are unknown. Increased pressure stimulated ATP release from the isolated uroepithelium of rabbit bladders, which was blocked by inhibitors of vesicular transport, connexin hemichannels, ABC protein family members, and nucleoside transporters. Pressure-induced increases in membrane capacitance (a measure of apical plasma membrane surface area where 1 µF ≈ 1 cm 2 ) were inhibited by the serosal, but not mucosal, addition of apyrase or the purinergic receptor antagonist PPADS. Upon addition of purinergic receptor agonists, increased capacitance was observed even in the absence of pressure. Moreover, knockout mice lacking expression of P2X 2 and/or P2X 3 receptors failed to show increases in apical surface area when exposed to hydrostatic pressure. Treatments that prevented release of Ca 2+ from intracellular stores or activation of PKA blocked ATPγS-stimulated changes in capacitance. These results indicate that increased hydrostatic pressure stimulates release of ATP from the uroepithelium and that upon binding to P2X and possibly P2Y receptors on the umbrella cell, downstream Ca 2+ and PKA second messenger cascades may act to stimulate membrane insertion at the apical pole of these cells.

The effect of hydrostatic pressure on ion transport in the bladder uroepithelium was investigated. Isolated rabbit uroepithelium was mounted in modified Ussing chambers and mechanically stimulated by applying hydrostatic pressure across the mucosa. Increased hydrostatic pressure led to increased mucosal-to-serosal Na+ absorption across the uroepithelium via the amiloride-sensitive epithelial Na+ channel. In addition to this previously characterized pathway for Na+ absorption, hydrostatic pressure also induced the secretion of Cl- and K+ into the mucosal bathing solution under short-circuit conditions, which was confirmed by a net serosal-to-mucosal flux of 36Cl- and 86Rb+. K+ secretion was likely via a stretch-activated nonselective cation channel sensitive to 100 microM amiloride, 10 mM tetraethylammonium, 3 mM Ba2+, and 1 mM Gd3+. Hydrostatic pressure-induced ion transport in the uroepithelium may play important roles in electrolyte homeostasis, volume regulation, and mechanosensory transduction.

Assessment of willingness to pay (WTP) has become an important issue in health care technology assessment and in providing insight into the risks and benefits of treatment options. We have accordingly explored the use of an interactive method for assessment of WTP. To illustrate our methodology, we describe the development and testing of an interactive tool to administer a WTP survey in a dental setting. The tool was developed to measure patient preference and strength of preference for three dental anesthetic options in a research setting. It delivered written and verbal formats simultaneously, including information about the risks and benefits of treatment options, insurance, and user-based WTP scenarios and questions on previous dental experience. Clinical information was presented using a modified decision aid. Subjects could request additional clinical information and review this information throughout the survey. Information and question algorithms were individualized, depending on the subject's reported clinical status and previous responses. Initial pretesting resulted in substantial modifications to the initial tool: shortening the clinical information (by making more of it optional reading) and personalizing the text to more fully engage the user. In terms of results 196 general population subjects were recruited using random-digit dialing in southwestern Ontario, Canada. Comprehension was tested to ensure the instrument clearly conveyed the clinical information; the average score was 97%. Subjects rated the instrument as easy/very easy to use (99%), interesting/very interesting (91%), and neither long nor short (72.4%). Most subjects were comfortable/very comfortable with a computer (84%). Indirect evaluation revealed most subjects completed the survey in the expected time (30 min). Additional information was requested by 50% of subjects, an average of 2.9 times each. Most subjects wanted this type of information available in the provider's office for use in clinical decision making (92%). Despite extensive pretesting, three "bugs" remained undiscovered until live use. We have demonstrated that the detailed information, complex algorithms, and cognitively challenging questions involved in a WTP survey can be successfully administered using a tailor-made, patient-based, interactive computer tool. Key lessons regarding the use of such tools include allowing the user to set the pace of information flow and tailor the content, engaging the user by personalizing the textual information, inclusion of tests of comprehension and offering opportunities for correction, and pretesting by fully mimicking the live environment.