Simultaneous recording of mechanical and intracellular electrical activity in guinea-pig urinary bladder smooth muscle: a comparison with human detrusor contraction.

OBJECTIVES: To study the relationship between the electrical and mechanical activity of guinea-pig detrusor muscle and compare this with the results obtained in human tissue. The guinea pig is the most used model to study the electrical basis of human bladder contraction.
METHODS: We simultaneously recorded the mechanical and intracellular electrical activity in muscle strips. To study the effect of tissue movement on the membrane potential, the medium was made hypertonic with sucrose. Carbachol and KCl were applied to the bath to induce contractions.
RESULTS: Carbachol resulted in a force response without a consistent change in the membrane electrical activity. KCl induced depolarization of the membrane associated with force development. Sucrose in the medium greatly impaired the ability to contract, without affecting the electrical activity. Compared with recordings in normal Krebs' solution, the resting membrane potential was not altered. In both media, spike-shaped potentials with variable amplitudes and shapes were recorded. These events were minimally affected by sucrose.
CONCLUSIONS: In contrast to the response to KCl, the overall mechanical response of guinea-pig detrusor strips to muscarinic receptor stimulation did not correlate with the electrical activity of a single cell. Sucrose had only a minimal effect on the electrical activity, demonstrating that the electrical responses we measured were not affected by movement. Our intracellular recordings in guinea-pig tissue differed from the results obtained by other groups, but show great resemblance with those we recorded in human urinary bladder smooth muscle strips.