Bladder dysfunction can be improved with therapeutic intervention on transient contractions in the bladder. The kidneys send waste and excess water to the bladder. Once the bladder reaches its threshold capacity a signal is sent through the central nervous system that it needs to be voided. This is how we know we need to go to the bathroom. But in addition to this filling pressure, the researchers uncovered that this mechanism also involved the so-called non-voiding transient contractions (TCs) in the smooth muscle of the bladder.
TCs do not send signals to indicate when the bladder is full, but rather indicate when the most efficient time for bladder voiding is. The researchers suggest that TCs offer a new therapeutic target when it comes to treating bladder dysfunction. Lead researcher Mark T. Nelson explained, “The presence or absence of these contractions, and how fast the contractions happen, can contribute to bladder under-activity or over-activity – which are both bad.”
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The researchers conducted their study using an ex vivo mouse bladder preparations. The researchers observed that with increased pressure, TCs evoke a 10 times greater increase in nerve activity. The researchers concluded that TCs are responsible for most of the bladder sensory signaling.
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Dr. Nelson added, “This meant that the rate of rise of the TC tells the brain not only how full the bladder is, but also if the bladder muscle can contract sufficiently for normal voiding. We have known for years that BK channels in urinary bladder smooth muscle cells help determine excitability. The more the channels are on, the less excitable the bladder smooth muscle becomes, the fewer of these transient contractions you have … But if we block SK channels, we get a much bigger burst of sensory nerve outflow. It looks like SK channels are in an interstitial cell type that is involved in sensing this small, but rapid, change in pressure.”
Future studies will focus on ways to determine frequency and rate of the rise of these transient contractions. Dr. Nelson concluded, “Transient contractions seem to vary from bladder to bladder. At least in our experiments, the frequency is set for that animal or person. It seems like it is fine-tuned, so that you get the optimal response. Our data suggest that other cell types – non-muscle cell types, non-nerve cell types – are playing a role.”
