E. van Asselt

Contractility parameters of the guinea pig bladder in situ: similarity to human bladder contractility.

The parameters P(isv) (active isovolumetric detrusor pressure) and Vmax (maximum shortening velocity), which characterize the contractility of the detrusor muscle, were determined in guinea pigs. To this end it was necessary to develop a method of measuring flow rates in these small animals. The values found were used to calculate the contractility parameter Wmax. Thirteen animals were used. The results found for P(isv) and Vmax were 43.0 +/- 3.7 cm. H2O and 20.2 +/- 3.7 mm. per second, respectively. The latter corresponded to about 0.38 muscle lengths per second, which is similar to values reported for bladder strips from other species. Previous work showed that in vitro P(isv) decreased with increasing bladder volume over a wide range of volumes. In vivo P(isv) seemed to be independent of bladder volume. This suggests that neurogenic stimulation intensifies as volume increases. Vmax also was independent of volume. Wmax appeared to be suitable for detecting differences in the contractility of the bladders of different animals. Values were not significantly different in isovolumetric and nonisovolumetric contractions. Normalized to the size of the bladder, the Wmax values indicated that the power generated by the guinea pig bladder is similar to the power generated by the human bladder.

Comparison of detrusor contractility of guinea pig bladders in situ and strips from these in vitro

To study the relative importance of neurogenic factors in detrusor contractility, active bladder wall stress values were compared in situ and in vitro. Eight male guinea pigs were used. The active stress in the bladder wall in spontaneous micturition contractions was calculated from the results of urodynamic examinations and compared with the active stress developed in response to optimum electrical stimulation in full-thickness bladder wall strips taken from the same bladders. The results indicated that, in normal micturition, the detrusor muscle is not fully stimulated, and the rate of pressure development is not determined by mechanical factors. To identify topological variations of detrusor contractility, the strips were taken from three different locations. It was found that strips from the posterior wall contracted more forcefully than those from the anterior wall.

A method for isolating smooth muscle cells from pig urinary bladder with low concentrations of collagenase and papain: the relation between calcium concentration and isolated cell length.

SummaryThe present study describes a method for isolating single smooth muscle cells from pig urinary bladder using a continuous resuspension device. Low concentrations of collagenase and papain were sufficient to obtain a high yield of viable smooth muscle cells, which remained viable for about 3–4 h as tested with fluorescein diacetate. Addition of fetal calf serum increased the lifespan of the isolated cells and the percentage of contractile smooth muscle cells, but caused spontaneous shortening of the cells. The length and volume of the isolated smooth muscle cells depended on the calcium concentration used in the isolation buffer solution. The isolated muscle cells were apparently relaxed if a calcium concentration less than 1.0 mmol/l was used in the isolation medium. In higher calcium concentrations the isolated cells were significantly shorter, probably as a result of a contraction caused by mechanical stimulation of the cells during the isolation procedure.

Contractile properties of inner and outer smooth muscle bundles from pig urinary detrusor

Like in the human detrusor, the pig urinary detrusor muscle consists of two layers: compactly arranged smooth muscle bundles on the mucosal side (inner layer) and loosely arranged smooth muscle bundles on the serosal side (outer layer). The contractile properties of muscle bundles of both layers were measured using the stop test followed by an isometric contraction. Total and passive forces were measured in ten muscle bundles from the inner and outer muscle layers. Active force was defined as the difference between total and passive force. The curvature and the unloaded shortening velocity of the force-velocity relation were calculated from the shortening forces measured during the stop test. The rate of force development was calculated from the isometric contraction. Differences in contractile properties between both layers were pairwise tested using the Wilcoxon Signed Ranks test. Percentage wise, the outer layer muscle bundles produced the highest active isometric force. The shortening forces were also higher in the outer layer bundles. As a result, both the curvature and the unloaded shortening velocity, derived from the average force-velocity relations fitted to the data sets, were higher in the muscle bundles from this layer. Finally, the outer layer muscle bundles contracted significantly faster than those of the inner layer. Muscle bundles from the outer layer of pig detrusor were found to be faster and stronger (more phasic) than the weaker and slower (more tonic) bundles from the inner layer, suggesting that during bladder contraction the outer layer of the detrusor does more work than the inner layer.

Cell length measurements in longitudinal smooth muscle strips of the pig urinary bladder

SummaryIn this study the length of smooth muscle cells in muscle bundles of pig urinary bladder wall was determined after dissection in Tyrode buffers with different calcium concentrations ([Ca2+]). Previous studies have shown that the length of isolated smooth muscle cells decreases with an increase in [Ca2+] in the buffer. Unlike the results in isolated cells, no significant differences in length were found between cells in strips subjected to different [Ca2+]. Cells in bundles dissected from filled bladders were significantly larger than those dissected from emptied bladders. Cells in strips from emptied bladders dissected in 1.8 mM Ca2+-Tyrode buffer were shorter than those obtained in Ca2+-free buffer. From the measurements it was concluded that: (1) Cell length in intact tissue is directly related to tissue length; series elastic structures external to the cells do not allow significant shortening of the cells. (2) Passive parallel elasticity outside the cells accounts for passive shortening when bladders are emptied manually. (3) Cell length is not related to empty bladder weight. (4) A positive relation exists between empty bladder weight and bladder capacity.

Why nerve signals should be measured monopolarly

A nerve signal, to which white noise was added, and monopolar and bipolar recordings of this signal were simulated. As a measure for nerve activity both signals were integrated (NA/sub mon/ and NA/sub bip/). The bipolar signal was rectified before integration. NA/sub MON/ appeared to be a linear measure for nerve activity while NA/sub bip/ underestimated it at high firing rates. Furthermore NA/sub mon/ was less sensitive to noise than NA/sub bip/. It was therefore concluded that the integrated non-rectified monopolar recording of a nerve signal is a better measure for the nerve activity than the integrated rectified bipolar recording.A nerve signal, to which white noise was added, and monopolar and bipolar recordings of this signal were simulated. As a measure for nerve activity both signals were integrated (NA/sub mon/ and NA/sub bip/). The bipolar signal was rectified before integration. NA/sub MON/ appeared to be a linear measure for nerve activity while NA/sub bip/ underestimated it at high firing rates. Furthermore NA/sub mon/ was less sensitive to noise than NA/sub bip/. It was therefore concluded that the integrated non-rectified monopolar recording of a nerve signal is a better measure for the nerve activity than the integrated rectified bipolar recording.

Can an algorithm predict a voiding contraction in unconscious rats

Urinary incontinence (UI) is a very common and serious disorder which can be classified in stress and urge incontinence, the latter mainly caused by an overactive bladder (OAB). A definitive treatment for OAB does not exist yet due to its complex nature. Therefore, more attention must be focused on improving the patients quality of life. A device able to alert the patient to development of a voiding contraction would be highly desirable, enabling actions to avoid incontinence. The main hypothesis of this work is that a voiding contraction is preceded by a consistent change in the pattern of intravesical pressure (pves). We developed an algorithm based on frequency analysis of pves recordings of two strains of rats whose bladders were first filled with saline (S fillings) and then with acetic acid (AA fillings); the latter was used as model for OAB in rats. The algorithm was designed to provide an alarm when an increase in the range 0.2-0.6Hz of the amplitude spectrum was detected. The accuracy of the algorithm has been tested and quantified, successful alarms were those taking place within fifty seconds before the start of voiding. Although the results are still very preliminary, due to the low number of tested animals, they seem encouraging since, in five rats, only one showed a percentage of success lower than 50%, with one rat reaching 100%. The accuracy of the algorithm is affected by the choice of the values for the controlling parameters, which have been set the same for all rats; future developments might include individual values for each rat.

A novel single compartment in vitro model: Perflurocarbons for electrophysiological studies of the rat urinary bladder

This study presents a novel single compartment model for in vitro electrophysiological studies of the rat urinary bladder. We tested the functionality and suitability of FC-770 (a Perflurocarbon) for in vitro recording of nerve activity arising from the bladder in a single compartment setup. We have also favorably tested stimulation of the bladder via the bladder nerves in FC-770. The organ viability was monitored by recording spontaneous contractions of the bladder for a certain time. We propose the use of FC-770 as a fluid for nerve recording/stimulation in vitro as well as for maintaining organ viability, over the commonly used two compartmental methods.