PubMed Health⌕ Search

Biomedical subjects

R Van Mastrigt

Publications and source records attributed to R Van Mastrigt.

At least 19 recordsLinked to original sources
PubMed2000

Simultaneous recording of mechanical and intracellular electrical activity in human urinary bladder smooth muscle.

OBJECTIVE: To elucidate the role of the membrane potential in human detrusor smooth muscle contraction, by simultaneously recording mechanical and intracellular electrical activity in muscle strips. Materials and methods The agonists acetylcholine and carbachol were applied to induce a contraction on muscarinic receptor stimulation; to block the response, atropine was added to the bath. The Ca2+ necessary for activating the contractile machinery can be recruited via two pathways: release from intracellular stores or influx from the extracellular matrix. High potassium was applied to induce Ca2+ influx through voltage-sensitive Ca2+ channels. RESULTS: There were significant changes in the force when agonist, antagonist and high potassium was administered. However, there were significant changes in membrane potential only when KCl was applied to the bath and not with muscarinic agonist or antagonist application. Activity in the form of spike potentials did not change significantly on applying any of the test substances. CONCLUSION: The present results indicate that the Ca2+ mobilized on M3 receptor stimulation originates primarily from intracellular stores, with no systematic changes in membrane potential. Atropine only caused a relaxation in muscle previously contracted by M3-receptor agonist stimulation; it had no effect on relaxed muscle strips.

Adult↗
PubMed1997

Neurophysiological modeling of voiding in rats: bladder pressure and postganglionic bladder nerve activity.

A model was developed that describes the relations between bladder pressure and both efferent and afferent nerve activity in postganglionic bladder nerves in urethan-anesthetized rats. Nerve activity was calculated as the 100-ms time integral of the rectified nerve signal. Afferent and efferent nerve signals were measured separately by crushing the nerve proximally or distally. A linear relation was found between bladder pressure and afferent nerve activity (fit error < 7%), and the relation between bladder pressure and efferent nerve activity was described by a low-pass filter (fit error < 90%). In most experiments, combined (efferent and afferent) nerve activity was measured. Absence of efferent nerve activity was assumed during the pressure decrease immediately after voiding. From this episode, the afferent nerve activity was estimated for the entire measurement. Efferent nerve activity was then estimated assuming linear addition in the bidirectionally conducting nerves. The model described the measured data very well (fit error < 7%), and the model parameters showed a good reproducibility in each rat (SD was approximately 30% of the mean).

Afferent Pathways↗
PubMed1996

The influence of extracellular Ca2+ on the time course of isovolumetric pressure development in the guinea-pig urinary bladder.

Isovolumetric contractions were induced electrically in five guinea-pig bladders in a 1.8 mM Ca2+ buffer solution at two different volumes. The rate of pressure development was studied by analysis of phase-plots, which are plots of the rate of change of intravesical pressure as a function of pressure. At relatively large volumes the rate of pressure development showed a biphasic nature, suggesting that two different processes were involved in different phases of contraction. Extracellular Ca2+ was manipulated to identify these processes. Removal of extracellular Ca2+ led to an 85% reduction of the maximum isovolumetric pressure in subsequent stimulations, but pressure developed faster. The biphasic nature of pressure development at large volumes tended to disappear. It was concluded that at large bladder volumes pressure development in this type of smooth muscle is determined by the release of intracellularly stored Ca2+ in the early phase of contraction. In the final phase the rate of pressure development is limited by the extracellular Ca2+ influx. At small bladder volumes the Ca2+ influx takes place at a higher rate, so that the contribution of intracellular Ca2+ release to pressure development could not be identified at these volumes.

Animals↗
PubMed1996

Neurogenic modulation of urethral resistance in the guinea pig.

PURPOSE: The resistance offered to urinary flow by the urethra is one of the factors determining the course of micturition. It was the aim of the present work to study the dependence of urethral resistance on the degree of relaxation of the urethra. MATERIALS AND METHODS: Experiments were done in the guinea pig. Ten animals were used. In 5 animals saline was forced through the (unrelaxed) urethra at imposed flow rates in the range of 1.1 to 43.0 ml. per minute while the urethral pressure was measured. Second degree polynomials were fitted to the pressure/flow data. In the other 5 animals micturition contractions were evoked and pressure/flow plots were derived from the measured signals. A straight line was fitted to the lowest pressure values at each flow rate in these plots. These pressure values represent the most relaxed state of the urethra in these voidings. RESULTS: The pressures measured in the unrelaxed urethra were much higher than the pressures measured during voiding in the same flow rate range, but the intercepts of the mathematical equations fitted to the pressure/flow data on the pressure axis were not significantly different in the 2 groups. CONCLUSIONS: The unrelaxed urethra has a much "steeper" pressure/flow characteristic than the relaxed urethra. However, the urethral closing pressure, that is, the intercept of the pressure/flow characteristic on the pressure axis, does not depend on the state of relaxation of the urethra.

Animals↗
PubMed1995

Neurogenic modulation of micturition: the relation between stimulation intensity and the maximum shortening velocity of the guinea pig detrusor muscle.

The course of micturition depends on bladder contractility and urethral resistance. The former is determined by geometrical, muscular and neurogenic factors. The muscular aspects of bladder contractility can be characterized by the parameters Pisv, the isovolumetric detrusor pressure, and vmax, the maximum (unloaded) shortening velocity of the detrusor muscle. The neurogenic control system of the urinary tract modulates bladder contractility, which might effectively change the values of Pisv and vmax. These parameters also depend on the instantaneous bladder volume. In previous work the dependence of Pisv on the intensity of stimulation and bladder volume was measured in guinea pig bladders in vivo and in vitro. In the present work vmax was derived in 5 guinea pig bladder in vitro, using electrical stimulation and the stop-flow technique. This technique implies that pressure values measured at a certain shortening velocity of the bladder circumference and in an isovolumetric contraction at the same volume are used to derive vmax mathematically from the Hill equation. vmax was independent of the bladder volume in the range of 0.6 to 6.1 ml., but it was significantly different for the two intensities of stimulation used. Therefore, it is concluded that the maximum shortening velocity of the guinea pig detrusor muscle depends on the intensity of stimulation. During submaximal stimulation the detrusor not only generates lower pressures, it also contracts more slowly. A possible explanation for this phenomenon is that the bladder is not uniformly stimulated. The isovolumetric pressure measured in the stop-flow test was compared with the isovolumetric pressure measured at the same bladder volume some minutes later. It was observed that shortening had a depressant effect of approximately 33% on the isovolumetric pressure. This implies that the clinically employed stop-flow test might underestimate detrusor contraction strength.

Animals↗
PubMed1995

A comparative study of voiding in rat and guinea pig: simultaneous measurement of flow rate and pressure.

In this study, the voiding phase of the micturition cycle in the anesthetized rat and guinea pig is analyzed. In both animals, voiding is characterized by an increase in intravesical pressure and then a decrease, which is accompanied by flow through the urethra and emission of urine. An ultrasonic flow probe was used in both species to measure the flow rate in relation to the intravesical pressure. In the (male) rat, so-called high-frequency oscillations are superimposed on the decreasing bladder pressure. These oscillations do not occur in the guinea pig. It is concluded that the high-frequency oscillations are caused by intermittent flow and not by variations in the bladder contraction. The intermittent flow most likely is caused by the relaxation and contraction of the external urethral sphincter and may have a function in territory marking. In our view, it is not likely that the oscillations enhance bladder emptying, as has been suggested in the literature.

Animals↗
PubMed1994

Photolysis of caged calcium using a low-cost flash unit: efficacy analysis with a calcium selective electrode.

Photolysis of caged calcium (Nitr5, Calbiochem) can be used to study calcium dependent processes such as excitation-contraction coupling and muscular mechanics. Expensive high energy light sources are routinely used for UV light exposure, but this study describes an alternative low cost xenon flash unit constructed in our laboratory. A 300 J short arc xenon flash lamp (Heimann) was mounted in an elliptical reflector and driven by a modified Metz 60 CT 4 photoflash unit up to 240 J input energy and 4 ms flash duration. A 20 microliters cuvette containing a test solution was placed in a complementary elliptical reflector. An ion selective calcium electrode was used to measure the free calcium concentration [Ca2+] before and after flash in test solutions containing 1.00 mM Nitr5 in combination with different added [Ca2+]s. Using this technique we estimated that 1 flash on 1.00 mM Nitr5 increased the free [Ca2+] from 10(-7) to 1.1 x 10(-5) M. When the added [Ca2+] was less than 2.3 x 10(-4) M, the used Nitr5 behaved as a strong calcium chelator because 23% of it was unloaded with calcium. It is concluded that a physiologically relevant change in free [Ca2+] can be evoked by photolysis of Nitr5 using a low cost (approximately $1500) xenon flash unit, and that ion selective Ca electrodes can be adequately used to monitor the resulting changes in [Ca2+].

Calcium↗
PubMed1993

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.

Animals↗
PubMed1992

Improved indication and followup in transurethral resection of the prostate using the computer program CLIM: a prospective study.

Analysis of preoperative and postoperative detrusor pressure-flow measurements with the aid of the IBM compatible software package CLIM in 29 patients who underwent transurethral prostatic resection indicated that CLIM supplies reliable obstruction parameters that are recommended for preoperative assessment and postoperative followup, and that approximately a third of the patients who present with prostatism are nonobstructed, suggesting that the indication for transurethral resection of the prostate is over assessed.

Adult↗
PubMed1992

The prognostic value of bladder contractility in transurethral resection of the prostate.

The contractility of the bladder as quantified by a parameter of approximated power per bladder surface area based on the Hill equation (Wmax) was calculated for 29 patients before and 3 months after transurethral resection of the prostate. There was no significant change in this parameter as a result of the operation. Patients who still had a significant amount of residual urine postoperatively had decreased contractility before and after surgery so that the postoperative condition could have been predicted preoperatively. In many patients a fading contraction was observed, that is detrusor contractility decreased during voiding, which gave rise to a significantly increased volume of residual urine. In most patients this pattern was restored to normal after relief of the obstruction, indicating that it was not related to structural changes in the detrusor muscle. A preoperative fading contraction had no predictive value towards the outcome of the operation.

Humans↗
PubMed1991

Excitatory pathways in smooth muscle investigated by phase-plot analysis of isometric force development.

Excitatory pathways in the smooth muscle of the pig urinary bladder were investigated using phase-plot analysis of isometric contractions. The phase plots, plots of the rate of change of the force as a function of the force itself, were dominated by a straight line described by the horizontal intercept (Fiso) and the vertical intercept (U). The quotient Fiso/U is a time constant that characterizes the rate-limiting step in isometric force development in the muscle. Bladder strips of 1 mm diameter were activated by electrical field stimuli, acetylcholine, potassium, and ATP in combination with selective pathway inhibitors such as verapamil, atropine, or a calcium-free solution containing ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. When pathways that depended significantly on depolarization or intracellular calcium release were selected, the time constant was significantly smaller, indicating a faster process. The results indicated that the rate-limiting step in force development was determined by the influx of extracellular calcium.

Animals↗
PubMed1990

Mechanical properties of mammalian single smooth muscle cells. III. Passive properties of pig detrusor and human a terme uterus cells.

Cells isolated from pig urinary bladders and pregnant full term human uteruses were attached longitudinally between a microforce transducer and a length displacement apparatus. Cells were stretched by applying a series of ramp-like length changes of 0.2 s duration and 10.0 microns amplitude at intervals of 15 min. Passive forces upon straining were as high as 70-100 microNs. Following these peak forces stress relaxation occurred, levelling off approximately 50% of the maximum peak force. The maximum elastic modulus estimated for single cells was found to be at least a tenfold higher than was previously estimated from intact bladder strips. The relation between the increase in length and the increase in initial force increment was found to be approximately linear. An exponential equation was fitted to a selected number of stress relaxation curves. Relaxation curves of bladder cells show a clearly different time course as compared to bladder tissue strips, suggesting that a significant amount of relaxation in strips has to be contributed to the connective tissue components or to structural changes in these strips.

Animals↗
PubMed1990

Mechanical properties of mammalian single smooth muscle cells. I. A low cost large range microforce transducer.

A transducer has been developed for measuring the minute forces generated during isometric contractions (1.0-10.0 microN) of single smooth muscle cells from the pig urinary bladder and the human uterus. In addition to its high sensitivity, resolution and stability (100 mV microN-1, and less than 0.1 microN and less than 2.0 microN h-1), the transducer features a very wide range (100-140 microN) with good linearity, enabling measurement of contractions as well as passive force-length characteristics within one uninterrupted measurement session. Since the transducer features an independent and interchangeable force to displacement conversion system, different force ranges can be realized by inserting force conversion systems with different compliances.

Animals↗
PubMed1990

Mechanical properties of mammalian single smooth muscle cells. II. Evaluation of a modified technique for attachment of cells to the measurement apparatus.

A method is described for attaching isolated single smooth muscle cells to an apparatus designed for measuring the longitudinal forces developed passively and actively by the cell upon straining, electrical or pharmacological stimulation. Primary attachment of the cell is based on its natural negative surface charge in combination with a positive surface charge on the micro-tools used for attaching. Definite attachment is obtained by a knotting technique. Results show that this method of attachment is reliable and strong enough to withhold forces exceeding those necessary to break or tear the cell. Although this method allows relatively short cells to be attached (L greater than 80 microns). alternative methods e.g. glueing, are necessary to attach the shortest smooth muscle cells.

Animals↗
PubMed1988

The length dependence of the series elasticity of pig bladder smooth muscle.

Strips of urinary bladder smooth muscle were subjected to a series of quick release measurements. Each measurement consisted of several releases and resets to the original length, made during one contraction. The complete length-force characteristic of series elasticity was quantified by estimating H, the amplitude of quick release necessary to reduce the active force to exactly zero, and Db, a measure for the deviation of the characteristic from a straight line. By measuring a series of contractions at increasing stretched strip lengths, the length dependence of these parameters was studied. It was found that H depends linearly on stretched strip length. On average H/length amounted to 0.04. Db decreased when strips were stretched, i.e. a straight line was more closely approximated. Both parameter dependencies support the concept of two separate elastic mechanisms, a linear true passive elasticity in series with a non-linear elasticity in the cross-bridges. For the latter, H amounts to 3.8% of the initial strip length.

Animals↗
PubMed1981

First results of stepwise straining of the human urinary bladder and human bladder strips.

A new method of cystometry called stepwise cystometry, based on a viscoelastic model of the urinary bladder wall, is proposed. This cystometry technique yields objective parameters, which provide information on the mechanical condition of the bladder wall. The method was tested on 21 patients. It was technically simple to perform. The parameters obtained were in good agreement with those derived from 105 measurements on 13 human bladder wall strips, provided that a correction was applied for the lower strain rates involved.

Elasticity↗