Bladder Science Abstracts
1. J Physiol. 2002 Jan 15;538(Pt 2):357-69.
The role of the L-type Ca(2+) channel in refilling functional intracellular Ca(2+) stores in guinea-pig detrusor smooth muscle.
Department of Medicine, University College London, 48 Riding House Street, London W1W 7EY, UK.
The transient rise of intracellular Ca(2+) in detrusor smooth muscle cells is due to the release of Ca(2+) from intracellular stores. However, it is not known how store refilling is maintained at a constant level to ensure constancy of the contractile response. The aim of these experiments was to characterise the role of L-type Ca(2+) channels in refilling. Experiments used isolated guinea-pig detrusor myocytes and store Ca(2+) content was estimated by measuring the magnitude of change to the intracellular [Ca(2+)] ([Ca(2+)](i)) after application of caffeine or carbachol using epifluorescence microscopy. Membrane potential was controlled when necessary by voltage clamp. After Ca(2+) stores were emptied they refilled with an exponential time course, with a time constant of 88 s. The value of the time constant was similar to that of the undershoot of [Ca(2+)](i) following store Ca(2+) release. The degree of store filling was enhanced by maintained depolarisation, or by transient depolarising pulses, and attenuated by L-type Ca(2+) channel antagonists. Inhibition of the sarcoplasmic reticular Ca(2+)-ATPase prevented refilling. Reduction of the resting [Ca(2+)](i) was accompanied by membrane depolarisation; under voltage clamp reduction of [Ca(2+)](i) decreased the number and magnitude of spontaneous transient outward currents. Ca(2+) release from intracellular stores, elicited by caffeine or carbachol, is independent of membrane potential under physiological conditions. However, store refilling occurs via Ca(2+) influx through L-type Ca(2+) channels. Ca(2+) influx is regulated by a feedback mechanism whereby a fall of [Ca(2+)](i) reduces the activity of Ca(2+)-activated K(+) channels, causing cell depolarisation and an enhancement of L-type Ca(2+) channel conductance.
2. Urology. 2009 Sep;74(3):691-6. Epub 2009 Jun 7.
Albany College of Pharmacy, Albany, NY 12203, USA.
To evaluate the effect ovariectomy (OVX) after 2 and 4 weeks on bladder function and biochemistry of the adult female rabbit urinary bladder.
Twelve mature female rabbits were divided into 3 groups: control, 2-week ovariectomized, and 4-week ovariectomized. At the end of the experimental period, the following studies were performed: contractile studies on isolated strips; examinations of the activity of citrate synthase (a marker for mitochondrial function) and thapsigargin-sensitive calcium ATPase (a marker for sarcoplasmic reticular calcium uptake function); and quantification of Rho-kinase (ROK) alpha and beta and myosin light chain kinase by Western blot analyses.
By 28 days after OVX, there were significant decreases in bladder weight, contractile responses, and citrate synthase and sarcoplasmic reticular calcium uptake activity. In addition, by 28 days following OVX the relative concentration of ROK alpha was significantly increased, whereas ROK beta concentration was significantly decreased. Myosin light chain kinase was significantly reduced.
Our study demonstrated that OVX contributed significantly to chronically decreased contractile function in the detrusor muscle of the female rabbit bladder, and this decrease, in turn, was mediated by decreased mitochondrial and sarcoplasmic reticulum function. These specific bladder dysfunctions could be related to the demonstrated decreased blood flow to the bladder muscle and mucosa and the increased generation of free radicals. Changes in smooth muscle regulatory proteins, especially myosin light chain kinase, may also play a role in contractile dysfunctions.
3. Mol Cell Biochem. 2007 Dec;306(1-2):213-9. Epub 2007 Aug 3.
Effect of aging on the response of biochemical markers in the rabbit subjected to short-term partial bladder obstruction.
Department of Pediatric Surgery, Gulhane Military Medical Faculty, Ankara, Turkey.
Partial bladder outlet obstruction (PBOO) results in marked biochemical alterations in the bladder. In this study, we focused on comparison of thapsigargin sensitive sarco/endoplasmic reticulum Ca(2+) ATPase activity (SERCA) and Citrate Synthase after short term PBOO in young versus old rabbits.
MATERIALS AND METHODS:
A total of 20 young and 20 mature male rabbits were divided into 4 sub-groups of 5 rabbits each (4 obstructed and 1 sham-control rabbit). The rabbits in the groups were evaluated after 1, 3, 7, and 14 days of obstruction, respectively. The activities of SERCA and citrate synthase were examined as markers for sarcoplasmic reticular calcium storage and release and mitochondrial function, respectively.
The SERCA activity of bladder body smooth muscle in the young animals increased at 7 and 14 days. For the old rabbits, the SERCA activity decreased significantly by 1 day and remained this level throughout the course of obstruction, and was significantly lower than young at all time periods. The citrate synthase activity in the young animals decreased over the 1-7 days, and then returned toward control level by 14 days following obstruction. In the old animals, citrate synthase activity of bladder body smooth muscle progressively decreased over the course of the study, and was significantly lower in the old than the young animals after 14 days obstructed.
The urinary bladders of the young rabbits have a considerable greater ability to adapt to PBOO than do those of the old rabbits. The deterioration of mitochondrial and SR function may be important mechanisms underlying geriatric voiding dysfunction.
4. Pharmacology. 1997 Dec;55(6):309-16.
Subcellular distribution of SERCA and calcium-activated ATPase in rabbit and human urinary bladder smooth muscle.Levin RM, Nicholas TJ, Snitkoff GG, Mandell J, Russell D, Wilbur HJ, Mogavero LJ.
SourceDepartment of Biological Science, Albany College of Pharmacy, NY 12208, USA.
AbstractPrevious studies have demonstrated that calcium storage and release from IP3-dependent sites in the sarcoplasmic reticulum play an important role in the contractile response of the rabbit urinary bladder to both field stimulation (mediated via neurotransmitter release) and bethanechol (direct muscarinic stimulation). In view of the importance of SERCA (see text) in urinary bladder smooth muscle function, we studied the distribution of SERCA by two methods; using Western blotting to quantitate the protein concentration and by enzyme analysis using thapsigargin to specifically inhibit SERCA. Rabbit and human samples of urinary bladder smooth muscle were homogenized and the homogenate separate into three particulate fractions by different centrifugation: the cell wall-nuclear, mitochondrial, and microsomal. The protein concentration of these three particulate fractions was determined and the SERCA protein level quantitated by Western blotting using SERCA-2 antibodies. The calcium ATPase activity was quantitated using standard enzymatic analysis and the thapsigargin sensitivity determined. The results demonstrated that (1) the concentration of SERCA was significantly greater in the microsomal fraction than in either of the other fractions for both rabbit and human bladder smooth muscle; (2) the enzymatic activities of both total calcium-activated ATPase and thapsigargin-sensitive calcium ATPase were evenly divided among the three fractions, and (3) the enzymatic activity of both total calcium-activated ATPase and thapsigargin-sensitive calcium ATPase of the rabbit exceeded that of the human. In conclusion, the distribution of SERCA and calcium ATPase of the rabbit bladder smooth muscle was similar to that in the human bladder smooth muscle, although activities in rabbit were significantly greater than those of human tissue.
5. J Urol. 1997 Feb;157(2):732-8.
Department of Surgery, University of Pennsylvania School of Medicine, Philadelphia, USA.
To investigate the effect of independently inhibiting calcium influx from extracellular sources and calcium release from intracellular stores on the ability of the urinary bladder to generate pressure and empty.
MATERIALS AND METHODS:
Rabbit bladders were mounted in an in vitro whole organ bath and filled with 15 ml. saline. Each bladder was incubated separately in Tyrode’s solution, with diltiazem (10 microM), to block extracellular calcium influx, or with thapsigargin (40 microM) and ryanodine (80 microM), to block the uptake and release of calcium from the sarcoplasmic reticulum. The bladder was then stimulated isometrically with field stimulation (32 Hz), and to empty with field stimulation and with bethanechol (250 microM), independently. During stimulation, transmural pressure and volume emptied were measured. From these, flow rate, power, and external mechanical work were calculated.
In the presence of diltiazem, the time to maximal pressure decreased while the rate of pressure generation increased. This results from increased participation of intracellular calcium release, which occurs rapidly and near the smooth muscle filaments, decreasing the diffusion time. In the presence of thapsigargin and ryanodine the maximal rate of pressure generation was decreased, due to the increased diffusion time required for calcium to move to the muscle filaments from extracellular sites.
The current study demonstrates that bladder pressure generation and emptying are dependent upon both an influx of calcium through L-type calcium channels (inhibited by diltiazem) and the stimulated release of calcium from the SR (inhibited by thapsigargin and ryanodine).