title: Evidence for a common mechanism for spontaneous rhythmic contraction and myogenic contraction induced by quick stretch in detrusor smooth muscle.
abstract: Detrusor smooth muscle exhibits myogenic contraction in response to a quick stretch (QS) as well as spontaneous rhythmic contraction (SRC); however, whether the same population of actomyosin crossbridges with a common regulatory mechanism is responsible for these two types of contraction has not been determined. Detrusor strips from New Zealand white rabbit bladders were allowed to develop SRC at a reference muscle length (L ref), or rhythmic contraction (RC) was induced with tetraethylammonium (TEA). Multiple 10-msec stretches of 15% L ref were then imposed at L ref randomly during the rhythm cycle, and the nadir-to-peak (NTP) tension amplitude of the resulting myogenic contraction was measured. The amplitude and period of the rhythm cycle were measured prior to each QS. NTP was larger when a QS was imposed during a portion the cycle when tension was smaller (n = 3 each SRC and TEA-induced RC). These data suggest that when the rhythmic mechanism was mostly inactive and tension was near a minimum, a larger portion of a shared population of crossbridges was available to produce a myogenic response to a QS. Rho kinase, cyclooxygenase-1, and cyclooxygenase-2 inhibitors (H-1152, SC-560, and NS-398) affected SRC amplitude and NTP amplitude following a QS to the same degree (n = 3 each drug), providing additional evidence to support the hypothesis that a common mechanism is responsible for SRC and myogenic contraction due to QS. If a common mechanism exists, then QS is a potential mechanical probe to study SRC regulation and its alteration in overactive bladder.
authors.affiliation: Department of Mechanical and Nuclear Engineering, Virginia Commonwealth University Richmond, Virginia, 23284.
authors.forename: S Omid
authors.initials: SO
authors.lastname: Komari
authors.affiliation: Department of Biomedical Engineering, Virginia Commonwealth University Richmond, Virginia, 23284.
authors.forename: Patrick C
authors.initials: PC
authors.lastname: Headley
authors.affiliation: Department of Surgery, Virginia Commonwealth University Richmond, Virginia, 23298.
authors.forename: Adam P
authors.initials: AP
authors.lastname: Klausner
authors.affiliation: Departments of Biochemistry & Molecular Biology and Pediatrics, Virginia Commonwealth University Richmond, Virginia, 23298.
authors.forename: Paul H
authors.initials: PH
authors.lastname: Ratz
authors.affiliation: Department of Mechanical and Nuclear Engineering, Virginia Commonwealth University Richmond, Virginia, 23284.
authors.forename: John E
authors.initials: JE
authors.lastname: Speich
keywords: Autonomous contraction; bladder; muscle twitch; phasic contraction; smooth muscle mechanics