Studies on the biphasic nature of urinary bladder contraction and function

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Abstract
The function of the urinary bladder is to store and expell urine. Micturition is accomplished via a coordinated, well‐sustained contraction of sufficient force to expel the entire contents of the urinary bladder. Studies in several labs have demonstrated that a functional bladder contraction consists of two phases: the first phase is represented by a rapid rise in intravesical pressure (isometric contraction) to a peak, followed by a prolonged period of increased (sustained) intravesical pressure (tension). Using isolated strip techniques, the in vitro whole bladder model, and several metabolic methodologies, we have studied contractile, functional, and biochemical parameters of these two phases of contraction.The results of our studies were as follows: 1) There was a small but significant decrease in net ATP at the peak of contraction, but not during the plateau phase. Creatine phosphate (CP) was significantly reduced at both times. 2) There was a rapid decrease in NADH fluorescence during the peak phase of contraction, which indicates an increase in oxidative metabolisvm. 3) The ED50 for the fluorescence response to bethanechol was significantly lower than the ED50 for contraction. 4) Whereas anoxia produced a gradual decline in both intracellular ATP and peak contraction, there was an immediate loss in the ability to maintain a contraction (ability of the bladder to empty).The results of these studies indicate that whereas preformed ATP mediates the initial contractile response to bethanechol, the plateau phase of bladder contraction (and the ability of the bladder to empty) may be mediated by high‐energy intermediates of oxidative phosphorylation (aerobic metabolism).