The Effect of Experimental Urethral Obstruction and its Reversal on Changes in Passive Electrical Properties of Detrusor Muscle

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Abstract
The passive electrical properties of guinea pig detrusor muscle were studied in order to determine how bladder outflow obstruction and reversal might modify the electrical activity of the bladder and, thus, contractility. Experimental bladder outflow obstruction was produced in guinea pigs and resulted in an increase in bladder weight with a decrease in spontaneous electrical activity, membrane time constant and space constant. In addition, the membrane Na-K pump activity increased with obstruction. Following reversal of obstruction, bladder weight gain associated with obstruction was only partially reversible. The decrease in the membrane time constant induced by obstruction was almost fully reversible following release of obstruction. In contrast, the membrane space constant which reflects spread of current, in addition to spontaneous electrical activity, were only partially reversible. The membrane Na-K pump activity of the detrusor muscle decreased to control levels following reversal of bladder outflow obstruction. There was no significant change in the resting membrane potential of detrusor smooth muscle with either obstruction or following reversal of obstruction. These results suggest, that, the changes in the bladder smooth muscle membrane electrical properties induced by experimental bladder outflow obstruction are only partially reversible following release of obstruction. Furthermore, the results suggest that, the dysfunctional cystometric patterns associated with bladder outflow obstruction might not only be due to changes in detrusor innervation but, fundamental reorganization of the detrusor's electrical syncytium with irreversible suppression of cell-to-cell transfer of electrical activity.