Analysis of the detrusor smooth muscle action potential

Ca2+ currents in smooth muscle cells isolated from human prostate

BACKGROUND

The objective of the investigation was to demonstrate the presence of voltage-dependent Ca2+ current in human prostate smooth muscle cells and to determine their biophysical characteristics.

METHODS

Prostate smooth muscle cells were isolated from biopsy samples of human prostates obtained from prostatectomy specimens or TURP chips. Electrophysiological recordings were made under current- or voltage-clamp using patch-type electrodes.

RESULTS

The average resting potential of prostate myocytes was 63 +/- 11 mV and action potentials (APs) could be elicited when K+ currents were blocked. With K-filled electrodes inward current was followed by a large outward component. When K+ currents were blocked a large Ca2+-sensitive inward current was measured. The inward current could be divided into two components, a fraction blocked by 30 microM verapamil and another by 20 microM NiCl2.

CONCLUSIONS

Based on the sensitivity to antagonists and holding potential both L-type and T-type Ca2+ channels were identified in human prostate smooth muscle.

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.

Recording the evoked canine detrusor electromyogram

With increasing interest in detrusor disorders and possible detrusor myopathies, a method for recording the detrusor electromyogram (detrusor-EMG) would probably greatly assist the diagnosis of various bladder dysfunctions. Therefore, we investigated the electromyographic activity of the detrusor during sacral root stimulation and during spontaneous bladder contractions in six anesthetized dogs. In all experiments, a high correlation of detrusor-EMG recordings with bladder contraction was observed. Analysis in the time domain and power spectrum analysis revealed the most clear correlation of detrusor-EMG with intravesical pressure rise in a frequency band above 3 Hz. The spike duration was 100 to 250 ms with an amplitude of 100 to 500 microV. Low-frequency activity below 1 Hz was mainly presumed to be artifacts due to fluid movement under the electrode. Our trials indicate that smooth muscle EMG recordings from the detrusor smooth musculature are possible. The exact physiological relevance of the signal in the sub-Hertz domain (<1 Hz) is still uncertain. The presented animal model allows the pathophysiologic investigation of various pathologies of bladder dysfunction and detrusor myopathies. Neurourol. Urodynam. 18:687-695, 1999.

Changes in action potential kinetics following experimental bladder outflow obstruction in the guinea pig

The effect of experimental bladder outflow obstruction on membrane electrical activity of guinea pig detrusor smooth muscle was studied. Using an intracellular microelectrode technique, action potentials were recorded from single smooth muscle cells to determine the effect of outflow obstruction on action potential (AP) kinetics. Bladder outflow obstruction resulted in smooth muscle hypertrophy with bladder weight gain to 2.7 times control levels after 8-12 weeks' obstruction. The changes in the AP kinetics noted with obstruction-induced bladder hypertrophy were a prolongation of the AP duration and a decrease in the maximum velocity of depolarization and repolarization. The AP amplitude, after hyperpolarization and overshoot potential in addition to the resting membrane potential (RMP) did not change significantly with bladder outflow obstruction. The values of these AP parameters were not affected significantly by the application of atropine and guanethidine in smooth muscle tissue from either control or obstructed bladders. These results suggest that the active electrical properties of the detrusor smooth muscle membrane are changed significantly by obstruction-induced bladder hypertrophy. Furthermore, the results suggest that adrenergic and cholinergic neurotransmitters do not contribute to these changes in AP kinetics following obstruction. The changes in AP properties with outflow obstruction-induced bladder hypertrophy were compared with those previously reported for the hypertrophic myocardium and were discussed in relation to the known impaired contractile properties of obstructed bladder smooth muscle.