Possible action of the proximal rhabdosphincter muscle in micturition of the adult male rat

Micturition requires high bladder pressure and simultaneous opening of the urethra. In adult male rat, a rhabdosphincter (RB) is known to be electrica lly active when the bladder pressure is high. This indicates a closure rath er than an opening of the urethra, which is inconsistent with the requireme nts of optimal urodynamics. In order to solve this problem, we simultaneous ly recorded electromyogram (EMG) of the proximal RB, bladder pressure, and Row rate. Micturition was evoked by an increased volume of saline in the bl adder. A computer-based recording device was used with minimal filtering. T he EMG was recorded with a monopolar flexible suction electrode. The suctio n electrode records action potentials resembling those obtained with a micr oelectrode technique. During the early high-frequency intraluminal pressure oscillation period (IPHFO). the increase of pressure initially associated with a decrease of potential of the RB. When the first how peak appeared. t he relationship of the bladder pressure and RB single EMG activities change d. The increasing pressure coincided with the positive potential wave (depo larisation). It was interrupted by a transient negative polarity period cal led transient repolarisation (TRP) coinciding with a Row rate peak. thus in dicating an opening of the RB lumen. After the TRP, the depolarisation cont inued. Additional experiments employing different methods are needed for po sitive identification of the TRP mechanism. (C) 2001 Wiley-Liss. Inc.