Submitted on December 30, 2008
Revised on February 23, 2009
Accepted on March 9, 2009
Bladder hyperactivity and increased excitability of bladder afferent neurons associated with reduced expression of Kv1.4 
-subunit in rats with cystitis
Yukio Hayashi1, Koichi Takimoto, MICHAEL B. Chancellor, Krisrtin A Erickson, Vickie L Erickson, Tsukasa Kirimoto, Koushi Nakano, William C de Groat, and Naoki Yoshimura1*
1 University of Pittsburgh
* To whom correspondence should be addressed. E-mail: nyos{at}pitt.edu.
Hyperexcitability of C-fiber bladder afferent pathways has been proposed to contribute to urinary frequency and bladder pain in chronic bladder inflammation including interstitial cystitis. However, the detailed mechanisms inducing afferent hyperexcitability after bladder inflammation are not fully understood. Thus, we investigated changes in the properties of bladder afferent neurons in rats with bladder inflammation induced by intravesical application of hydrochloric acid. Eight days after the treatment, bladder function and bladder sensation were analyzed using cystometry and an electrodiagnostic device of sensory function (Neurometer), respectively. Whole-cell patch-clamp recordings and immunohistochemical staining were also performed in dissociated bladder afferent neurons identified by a retrograde tracing dye, Fast Blue, injected into the bladder wall. Cystitis rats showed urinary frequency that was inhibited by pretreatment with capsaicin and bladder hyperalgesia mediated by C-fibers. Capsaicin-sensitive bladder afferent neurons from sham rats exhibited high thresholds for spike activation and a phasic firing pattern whereas those from cystitis rats showed lower thresholds for spike activation and a tonic firing pattern. Transient A-type K+ current density in capsaicin-sensitive bladder afferent neurons was significantly smaller in cystitis rats than in sham rats although sustained delayed-rectifier K+ current density was not altered after cystitis. The expression of Kv1.4 
-subunits, which can form A-type K+ channels, was reduced in bladder afferent neurons from cystitis rats. These data suggest that bladder inflammation increases bladder afferent neuron excitability by decreasing expression of Kv1.4 -subunits. Similar changes in capsaicin-sensitive C-fiber afferent terminals may contribute to bladder hyperactivity and hyperalgesia due to acid-induced bladder inflammation.
