Date of Award

1-1-2012

Document Type

Campus Access Thesis

Department

Biomedical Science

First Advisor

Georgi V Petkov

Abstract

Overactive bladder (OAB), often characterized by increased detrusor smooth muscle (DSM) contractility, is a highly prevalent disorder affecting ~17% of the US population. The current pharmacotherapy for OAB consists of antimuscarinics which have many adverse side effects and limited efficacy. Therefore, the identification of novel targets with better efficiency is urgently needed. This study presents the transient receptor potential melastatin 4 (TRPM4) channel, a Ca2+-activated, monovalent cation selective channel as a promising novel target for OAB therapies. Until now, the expression and function of the TRPM4 channels in DSM has not yet been explored. Here, we provide the first molecular and functional evidence for the presence of the TRPM4 channels in rat and guinea pig DSM. We detected the expression of the TRPM4 channels at mRNA levels in freshly isolated rat DSM single cells and DSM tissue using RT-PCR. Western blot and immunocytochemistry experiments demonstrated the expression of the TRPM4 channels in whole DSM tissue and freshly isolated DSM cells with specific localization on the plasma membrane in both rat and guinea pig. 9-phenanthrol, a recently characterized selective inhibitor of the TRPM4 channels, was used to examine their role in DSM function. Isometric DSM tension recordings revealed that 9-phenanthrol (0.1-30 μM) significantly inhibited the spontaneous phasic, pharmacologically-induced, and nerve-evoked contractions in rat DSM isolated strips with IC50 values of 1-6 μM. Similarly, in guinea pig DSM isolated strips, 9-phenanthrol significantly inhibited pharmacologically-induced and nerve-evoked contractions with IC50 values of 1-7 μM. 9-phenanthrol also reduced nerve-evoked contraction amplitude induced by continuous repetitive electrical field stimulation of 10 Hz frequency and shifted the frequency-response curve (0.5-50 Hz) relative to the control in both rat and guinea pig DSM isolated strips. The effect of 9-phenanthrol on contraction amplitude, force integral, and tone had comparable effects in both rat and guinea pig DSM isolated strips. In conclusion, this is the first study to examine the expression and provide functional evidence for the TRPM4 channels as critical regulators of rat and guinea pig DSM contractility. Future studies in human DSM are needed to validate the TRPM4 channel as a novel therapeutic target for OAB.

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