The decompensated detrusor V: molecular correlates of bladder function after reversal of experimental outlet obstruction

Abstract

Purpose: Calcium ion homeostasis has a significant role in smooth muscle function. Its regulation requires complex storage and release mechanisms via ion pumps and channels located within intracellular storage sites (sarcoplasmic reticulum) and at the plasma membrane. We have previously reported a dramatic loss of the 2 major sarcoplasmic reticulum proteins sarcoplasmic endoplasmic reticulum calcium magnesium adenosine triphosphatase (SERCA2) and the ryanodine sensitive ion channel, also called the ryanodine receptor, after outlet obstruction. In our current study we investigated the correlation of the expression of these 2 major sarcoplasmic reticulum components with bladder function recovery after the reversal of outlet obstruction.

Methods and methods: Standard partial bladder outlet obstruction was created in adult New Zealand White rabbits. Voiding patterns were monitored 2 and 4 weeks postoperatively, and rabbits were selected for outlet obstruction reversal based on a voiding pattern consistent with a decompensated state, as indicated by a frequency of greater than 30 voids daily and an average voided volume of less than 4 cc. Bladder biopsy was done when outlet obstruction was reversed. Voiding performance was monitored postoperatively and the animals were sacrificed 2 weeks later. Voiding patterns and muscle strip studies enabled us to define 2 functional outcome categories after reversal, namely normal versus minimally improved. Microsomal membrane protein fractions were prepared from the same bladder tissues before and after reversal, and probed by Western blot analysis for SERCA2 and ryanodine receptor expression.

Results: Western blot analysis revealed a major loss of SERCA2 and ryanodine receptor expression at the time of reversal and biopsy. In 65% of bladders obstruction reversal resulted in a normalized voiding pattern with a recovery of ryanodine receptor expression that was 15% to 65% of control values. In contrast, in the 35% of bladders with persistent voiding symptoms there was minimal recovery of ryanodine receptor expression. SERCA2 expression increased slightly in each group after reversal but did not differ in bladders with normalized versus improved function.

Conclusions: Bladder decompensation is highly associated with a loss of sarcoplasmic reticulum function. Furthermore, the decompensated detrusor recovers function after obstruction reversal, which is associated with the recovery of these sarcoplasmic reticulum components.