The elusive electromyogram in the overactive bladder: a spark of understanding

Abstract

It has been said that a technique capable of recording a urinary bladder electromyogram could be useful in the clinical evaluation of the detrusor neuropathies and myopathies implicated in the generation of lower urinary tract symptoms. However, in contrast to electromyography of skeletal and cardiac muscle, detrusor smooth muscle electromyography has remained in its infancy despite 50 years of scientific effort. The principal problems appear to be isolation of the real signal from artefacts, and the doubtful existence of electromyographic activity during cholinergic muscle contraction. The discovery of purinergic neuromuscular transmission in the overactive human bladder has renewed interest in detrusor electromyography as, in contrast to cholinergic mechanisms, purinergic mechanisms can generate extracellular electrical activity. In this paper, the development and validation of a novel technique for recording electrical activity from neurologically intact guinea-pig and human detrusor in vitro is described. A purinergic electromyographic signal is characterised and it is shown that detrusor taken from overactive human bladders has a greater propensity to generate electromyographic activity than normal by virtue of an aberrant purinergic mechanism.

Figure 1

Schematic diagram illustrating the mechanisms of contractile activation and associated extracellular electrical activity by acetylcholine and adenosine triphosphate in the detrusor muscle cell.

Figure 2

Schematic diagram showing the experimental apparatus for recording simultaneous electrical and mechanical activity from a whole guinea-pig bladder preparation.

Figure 3

Representative traces of electrical and mechanical activity recorded from an isolated whole guinea-pig bladder showing the electrical signal (circled) unchanged by repetitive stimulated contractions (A) and reversibly sensitive to α,β-mATP (B).

Figure 4

Representative traces of electrical and mechanical activity recorded from a human detrusor strip preparation showing sensitivity of the electrical signal (circled) to α,β-mATP (A), but not changed with atropine (B).

Figure 5

Diagram showing relationship between atropine-resistant contractions, and expression of an electrical signal for 24 human detrusor samples taken from clinically characterised human bladders. Each circle represents a bladder strip: filled circles indicate a bi-phasic α,β-mATP-sensitive electrical signal was recorded; open circles indicate no electrical signal could be recorded.