No conflict of interest reported by the author(s).
Original Basic Science Article
Smooth muscle caveolae differentially regulate specific agonist induced bladder contractions†
Article first published online: 22 NOV 2006
Copyright © 2006 Wiley-Liss, Inc.
Neurourology and Urodynamics
Volume 26, Issue 1, pages 71–80, January 2007
How to Cite
Cristofaro, V., Peters, C.A., Yalla, S.V. and Sullivan, M.P. (2007), Smooth muscle caveolae differentially regulate specific agonist induced bladder contractions. Neurourol. Urodyn., 26: 71–80. doi: 10.1002/nau.20361
- Issue published online: 8 JAN 2007
- Article first published online: 22 NOV 2006
- Manuscript Accepted: 7 SEP 2006
- Manuscript Received: 5 JUN 2006
- Office of Research and Development, Medical Research Service, Department of Veterans' Affairs, Washington, D.C.
- PHS Grant. Grant Number: RO1DK55086-01
- smooth muscle
Caveolae are cholesterol-rich plasmalemmal microdomains that serve as sites for sequestration of signaling proteins and thus may facilitate, organize, and integrate responses to extracellular stimuli. While previous studies in the bladder have demonstrated alterations in caveolae with particular physiologic or pathologic conditions, little attention has been focused on the functional significance of these organelles. Therefore, the purpose of this study was to investigate the role of caveolae in the modulation of receptor-mediated signal transduction and determine the presence and localization of caveolin proteins in bladder tissue.
Contractile responses to physiologic agonists were measured in rat bladder tissue before and after disruption of caveolae achieved by depleting membrane cholesterol with methyl-β-cyclodextrin. Stimulation with agonists was repeated after caveolae were restored as a result of cholesterol replenishment. RT-PCR, immmunohistochemistry, and Western blotting were used to determine the expression and localization of caveolin mRNA and proteins.
Following caveolae disruption, contractile responses to angiotensin II and serotonin were attenuated, whereas responses to bradykinin and phenylephrine were augmented. Cholesterol replenishment restored responses towards baseline. Carbachol and KCl induced contractions were not affected by caveolae disruption. Ultrastructure analysis confirmed loss of caveolae following cholesterol depletion with cyclodextrin and caveolae restoration following cholesterol replacement. Gene and protein expression of caveolin-1, -2, and -3 was detected in bladder tissue. Immunoreactivity for all three caveolins was observed in smooth muscle cells throughout the bladder.
The functional effects of cholesterol depletion on specific agonist-induced contractile events and the expression of all three caveolins in bladder smooth muscle support a central role for caveolae in regulation of selective G-protein-coupled receptor signaling pathways in bladder smooth muscle. Thus, caveolae serve to differentially regulate bladder smooth muscle by a stimulus-dependent potentiation or inhibition of bladder contraction. Neurourol. Urodynam. © 2006 Wiley-Liss, Inc.