Summary: Analysis of hydrostatic pressure-induced changes in
umbrella cell surface area
Edward Wang, Steven Truschel, and Gerard Apodaca*
Renal-Electrolyte Division, Department of Medicine, Laboratory of Epithelial Cell Biology, and Department of Cell Biology and Physiology,
University of Pittsburgh, 982 Scaife Hall, 3550 Terrace Street, Pittsburgh, PA 15261, USA
Accepted 2 February 2003
All cells experience and respond to external mechanical stimuli including shear stress, compression, and hydrostatic pressure.
Cellular responses can include changes in exocytic and endocytic traffic. An excellent system to study how extracellular forces govern
membrane trafficking events is the bladder umbrella cell, which lines the inner surface of the mammalian urinary bladder. It is
hypothesized that umbrella cells modulate their apical plasma membrane surface area in response to hydrostatic pressure. Un-
derstanding the mechanics of this process is hampered by the lack of a suitable model system. We describe a pressure chamber that
allows one to increase hydrostatic pressure in a physiological manner while using capacitance to monitor real-time changes in the
apical surface area of the umbrella cell. It is demonstrated that application of hydrostatic pressure results in an increase in umbrella
cell apical surface area and a change in the morphology of umbrella cells from roughly cuboidal to squamous. This process is
dependent on increases in cytoplasmic Ca2þ
. This system will be useful in further dissecting the mechanotransduction pathways
involved in cell shape change and regulation of exocytic and endocytic traffic in umbrella cells.
Ó 2003 Elsevier Science (USA). All rights reserved.
Keywords: Umbrella cell; Bladder; Endocytosis; Exocytosis; Pressure chamber; Mechanical stimuli; Capacitance