Intracellular recording of spontaneous electrical activity in human urinary bladder smooth muscle strips

We studied the spontaneous electrical activity of human urinary bladder smooth muscle strips, with the eventual aim of uncovering the mechanism underlying the clinical syndrome of the unstable bladder. Intracellular microelectrodes were used to record the membrane potentials of detrusor cells in muscle bundles originating from biopsy samples. Spontaneous spike-shaped potential fluctuations were analysed automatically. The membrane potential at the start of the potential change (V(start)), amplitude, duration at 10% of the amplitude (d(10%)), and upstroke velocity (DeltaV/Deltat) were estimated and statistically analysed. The mean resting membrane potential of the detrusor strip cells was -42 mV (SD: 9 mV). Different types of spontaneous activity could be recorded. On successive impalements within one preparation, the type of activity varied from one single spike-shaped potential to extensive bursts and was not correlated to the resting membrane potential. There was a large variation in size and shape of the spike-shaped potentials between the biopsy samples and even within one cell. The results provide the first description of spontaneous electrical activity in human detrusor smooth muscle strips. This activity is asynchronous, which could aid to maintain a low pressure in the bladder. Most likely, this spontaneous detrusor activity is myogenic in origin.