A new approach to recording the electromyographic activity of detrusor smooth muscle

Purpose: Extracellular recordings from the whole intact mammalian bladder o f the electrical events leading to contraction of the organ have been elusi ve for almost 50 years despite the widespread potential applications of suc h a technique. The principal problem is the need to isolate the small real signals reflecting membrane depolarization from the large electromechanical artifact generated as the organ contracts. In this preliminary study we de termined whether electrical signals may be isolated and verified as biologi cal using extracellular bipolar reversible suction electrodes. Materials and Methods: Six whole excised guinea pig bladders were mounted i n an especially constructed organ bath. Electrical activity resulting from nerve stimulation of the organ was recorded using a novel 10 bipolar Pt/PtC l suction electrode simultaneously with changes in intravesical pressure. M echanical and pharmacological control experiments were performed to determi ne the true origin of these signals. Results: A predominantly biphasic electrical signal of a mean amplitude plu s or minus standard deviation of 647 plus or minus 301 muV. and a mean dura tion of 293 plus or minus 51 milliseconds was consistently recorded from th e serosal surface of all guinea pig bladders. In all cases the electrical s ignal and mechanical response to stimulation were completely abolished by 1 muM. tetrodotoxin. The signal always preceded any change in intravesical p ressure. It was sensitive to changes in the CaCl2 concentration of the supe rfusate, abolished by purinergic but not cholinergic neuromuscular blockade and independent of electromechanical artifact. Conclusions: In this preliminary report we describe a novel technique by wh ich nerve mediated detrusor electrical activity leading to contraction of t he whole intact guinea pig bladder may be isolated from artifact and verifi ed as real. We hope that development of this technique may enable its appli cation to the in situ human bladder. However, to our knowledge whether elec tromyographic activity may be recorded from human detrusor remains to be de termined.