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A F Brading

Publications and source records attributed to A F Brading.

At least 37 records · Page 2Linked to original sources
PubMed2000

Abnormal contractile properties of rectal smooth muscle in chronic ulcerative colitis.

BACKGROUND: Patients with ulcerative colitis have abnormal rectal motility. AIM: To compare the contractile properties of rectal smooth muscle from patients with ulcerative colitis and controls. METHODS: Rectal smooth muscle strips from patients undergoing resection for ulcerative colitis or cancer (control) were mounted in an organ bath. The effects of carbachol (receptor-mediated) and potassium (causes membrane depolarization) were studied. Acetylcholinesterase histochemistry was performed and nerve counts compared. RESULTS: Ulcerative colitis (n=41) and control (n=34) strips contracted in response to potassium and carbachol. Mean (S.E. M.) maximum response to potassium in the control and ulcerative colitis groups was 1.07 (0.06) g/mg and 1.02 (0.09) g/mg tissue, respectively (P=N.S.). EC50s (concentrations required to give 50% of maximal response) were 75 (1) mM and 73 (1) mM, respectively (P=N.S. ). Although maximum responses to carbachol were similar, 2.12 (0.12) g/mg and 1.95 (0.12) g/mg tissue (P=N.S.), ulcerative colitis strips exhibited an increased sensitivity to carbachol, EC50s: 5.05 x 10-6 (0.55 x 10-6) M vs. 8.36 x 10-6 (0.88 x 10-6) M, P=0.002). There was no significant difference in nerve counts between the tissues, as assessed by staining for acetylcholinesterase. CONCLUSIONS: Ulcerative colitis tissue has an increased sensitivity to carbachol and this is not due to denervation; it may result from increased calcium release from intracellular stores since contraction due to membrane depolarization is not altered. Modulation of this pathway could potentially be used to alter rectal motility in patients with ulcerative colitis.

Acetylcholinesterase↗
PubMed2000

The effect of bladder outlet obstruction on tissue oxygen tension and blood flow in the pig bladder.

OBJECTIVE: To investigate the effect of partial bladder outlet obstruction on detrusor blood flow and oxygen tension (PdetO2) in female pigs. MATERIALS AND METHODS: Detrusor-layer oxygen tension and blood flow were measured using oxygen-sensitive electrode and radiolabelled microsphere techniques in five female Large White pigs with a partial urethral obstruction and in five sham-operated controls. The effects of chronic outlet obstruction on bladder weight, and cholinergic nerve density and distribution, are also described. RESULTS: In the obstructed bladders, blood flow and oxygen tension were, respectively, 54.9% and 74.3% of control values at low bladder volume, and 47.5% and 42.5% at cystometric capacity. Detrusor blood flow declined by 27.8% and 37.5% in the control and obstructed bladders, respectively, as a result of bladder filling, whilst PdetO2 did not decrease in the controls, but fell by 42.7% in the obstructed bladders. Bladder weight increased whilst cholinergic nerve density decreased in the obstructed animals. CONCLUSION: In pigs with chronic bladder outlet obstruction, blood flow and oxygen tension in the detrusor layer were lower than in control animals. In addition, increasing detrusor pressure during filling caused significantly greater decreases in blood flow and oxygen tension in the obstructed than in the control bladders.

Animals↗
PubMed2000

The contribution of cholinergic detrusor excitation in a pig model of bladder hypocompliance.

OBJECTIVE: To investigate the role of cholinergic excitation in mediating changes in detrusor compliance (manifested on conventional cystometry as an incremental rise in detrusor pressure as bladder volume increases) under conditions of propofol-sedation in the pig. Materials and methods Consecutive cystometrograms (CMGs) were obtained from eight female Large White pigs at a bladder filling rate of 50 mL/min. The first CMG was obtained while the pig was awake and unsedated. Two subsequent CMGs were obtained after light to moderate sedation with propofol (2-8 mg/kg/h) before and after the administration of intravenous atropine (0.02 mg/kg). RESULTS: All bladders were highly compliant over the volumes instilled (before sedation) with a maximum pressure during the filling phase of 0.9 cmH2O and a compliance of 943 mL/cmH2O. After sedation with propofol, the maximum pressure during the filling phase increased to 14 cmH2O with a compliance of 69 mL/cmH2O. Atropine antagonized this change in compliance; after sedation and atropine, the maximum pressure during the filling phase decreased to 4 cmH2O (P < 0.05) and the compliance increased to 337 mL/cmH2O (P < 0.05). CONCLUSION: The decrease in compliance seen in the pig bladder after sedation with propofol is mediated via muscarinic excitation. This probably occurs as a result of low-level tonic release of acetylcholine by the efferent parasympathetic nerves. The existence of such efferent excitatory activity during the storage phase in the overactive human bladder might explain the efficacy of bladder-selective muscarinic antagonists in a proportion of patients with detrusor hyper-reflexia and instability.

Animals↗
PubMed2000

Possible underestimation of the channel conductance underlying pinacidil-induced K+ currents using noise analysis in pig urethral myocytes.

Electrophysiological and pharmacological properties of the pinacidil-induced K+ currents in isolated cells from pig urethra were investigated using patch-clamp techniques. Pinacidil (100 microM) induced an outward current at -50 mV which gradually decreased. Under current-clamp conditions, 100 microM pinacidil induced a hyperpolarization that was sustained. This suggests that activation of only a few channels can hyperpolarize the membrane. At a holding potential of -50 mV, glibenclamide inhibited the pinacidil-induced current with a single exponential time course. Unitary current recordings in symmetrical 140 mM K+ conditions demonstrated that pinacidil activates a 43-pS, glibenclamide-sensitive K+ channel (i.e. K(ATP) channel). Analysis of the basal noise of the pinacidil-induced macroscopic currents from -90 mV to -30 mV yielded estimates of channel conductance (6 pS) which were much smaller, and probably an underestimate. These results indicate that pinacidil induces a glibenclamide-sensitive K+ current through only one type of K+ channel (K(ATP) channel) in pig urethra.

Animals↗
PubMed2000

Electrical coupling in smooth muscles. Is it universal?

There is strong experimental evidence for electrical coupling in all types of smooth muscle. In some publications, and particularly in physiological textbooks, smooth muscles are still divided into those that are electrically coupled and those that are not. In this article we review the evidence for the universal presence of coupling in smooth muscles and the underlying mechanism, which, in most cases, appears to be gap junctions. We propose a classification of smooth muscles based on the mechanisms that initiate their activity. The two main types of smooth muscle according to this classification are neurogenic (e.g., iris, arterioles, vas deferens) and myogenic (e.g., urinary bladder, intestine, most blood vessels).

Animals↗
PubMed2000

Radiotelemetered cystometry in pigs: validation and comparison of natural filling versus diuresis cystometry.

PURPOSE: Cystometry has previously been performed in awake animals using vesical and abdominal catheters, and artificial bladder filling. Conventional urodynamic recordings may be obtained in this manner, albeit under nonphysiological and potentially stressful conditions. Therefore, we developed a technique to perform continuous, ambulatory cystometric monitoring in pigs. MATERIALS AND METHODS: A dual pressure radiotelemetry device was surgically implanted in 22 large white pigs. Vesical and abdominal pressures were recorded and validated, subtracted detrusor pressures were derived and natural fill and diuresis cystometry was compared. RESULTS: Continuous recordings were obtained for 1 to 24 hours, and the devices remained in the animals for up to 3 months. There were few complications and incrustation of the intravesical catheter tip occurred but it did not appear to affect recorded pressures. The pressure data were validated by comparison with filling pressures during bladder distention and simultaneous conventional cystometry at the end of the experimental period. Comparison of natural filling and diuresis cystometrograms showed that natural bladder filling results in higher maximum detrusor pressure during voiding (38.1 versus 33.9 cm. H2O, p <0.05), higher detrusor pressure after contractions (42.6 versus 32.2 cm. H2O, p <0.05) and more frequent detection of unstable contractions in pigs with detrusor instability secondary to experimental manipulation of the lower urinary tract (77.8% versus 45.0%, p <0.05). CONCLUSIONS: This technique allows continuous cystometric monitoring in less stressed animals under more physiological conditions for relatively long periods and, thus, allows prolonged assessment of bladder function in pigs in response to pathological and pharmacological manipulations. Nonphysiological rates of bladder filling have been shown to result in detrusor inhibition, which emphasizes the importance of ambulatory cystometry when describing bladder function.

Animals↗
PubMed1999

Effects of phosphorylation-related drugs on slow Ca2+ tail current in guinea-pig detrusor cells.

In isolated guinea-pig detrusor cells, large conditioning depolarizations evoke slowly deactivating Ca2+ tail currents, considered to represent the second open state. The possible involvement of channel phosphorylation in this open state was examined. Application of isoprenaline caused a marginal increase in Ca2+ channel current evoked by simple depolarization, while forskolin did not. During application of either drug, slow-tail currents were never observed after simple depolarizations. The conditions necessary to induce slow-tail currents were not changed, even when cyclic AMP, ATP-gamma-S (adenosine 5'-O-(3-thiotriphosphate)), GDP-beta-S (guanosine 5'-O-(2-thiodiphosphate)) (in the pipette) or H-7 (1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride) (to the bathing solution) was applied. The frequent depolarization protocol, known to facilitate Ca2+ current via Ca2+ and cyclic AMP-dependent phosphorylation mechanism(s) in cardiac myocytes, did not induce slow-tail currents. These results suggest that the transition of Ca2+ channels to the second open state during large depolarization is not a result of (voltage-operated) channel phosphorylation itself. Possible underlying mechanisms are discussed.

Adrenergic beta-Agonists↗
PubMed1999

Glibenclamide-sensitive K+ channels underlying levcromakalim-induced relaxation in pig urethra.

To investigate the possible mechanisms involved in the stable and long-lasting levcromakalim-induced relaxation of the resting urethral tone, we have performed mechanical and voltage-clamp experiments using intact tissue and isolated cells from pig urethra, respectively. At negative membrane potentials, levcromakalim induced time- and voltage-independent membrane currents in whole-cell configurations. In cell-attached patches, levcromakalim not only increased the open-state probability (the NP(0) value) of the glibenclamide-sensitive 43 pS K+ channel (K(GS)) in a concentration-dependent manner, but also activated K(GS) with a time- and voltage-independence. During long burst-like channel activity, neither the mean open lifetime nor the mean closed time of K(GS) exhibited voltage-dependency between -100 and - 40 mV. It is concluded that levcromakalim causes a stable and potent relaxation of pig urethra through opening of K(GS) which possesses time- and voltage-independent activating mechanisms.

Animals↗
PubMed1999

Effects of nifedipine on anorectal smooth muscle in vitro.

INTRODUCTION: Glyceryl trinitrate reduces anal resting pressure and aids the healing of anal fissures. However, some patients develop tachyphylaxis and the fissure fails to heal, suggesting that other agents are needed. This study assesses the effects of nifedipine (a calcium channel antagonist) in modulating resting tone and agonist-induced contractions in human internal anal sphincter (IAS) and rectal circular muscle. METHODS: Smooth muscle strips from the IAS and rectal circular muscle from ten patients undergoing surgical resection were mounted for isometric tension recording in a superfusion organ bath. The effects of noradrenaline and carbachol were assessed in the presence of various perfusates. RESULTS: LAS strips developed tone and spontaneous activity. Noradrenaline produced dose-dependent contractions. In calcium-free Krebs solution, tone and activity were abolished and no contractions were elicited in response to noradrenaline. Nifedipine also abolished tone and spontaneous activity, but contractions to noradrenaline were only slightly attenuated. In contrast, rectal smooth muscle strips developed spontaneous activity but no resting tone and contracted in response to carbachol. In calcium-free Krebs solution, the spontaneous activity and carbachol contractions were abolished. Addition of nifedipine to the perfusate abolished spontaneous activity and greatly reduced contractions. DISCUSSION: These data suggest that spontaneous activity and resting tone are dependent on extracellular calcium and flux across the cells. Agonist-induced contraction in the IAS is attributable mainly to the release of calcium from intracellular stores, whereas rectal circular smooth muscle depends principally on extracellular calcium entering the cell for contraction. The attenuation of contractions in both tissues and the abolition of resting tone in the IAS suggest that nifedipine may be useful in the management of patients with anorectal disorders.

Adult↗
PubMed1999

Differences in contractile properties of anorectal smooth muscle and the effects of calcium channel blockade.

BACKGROUND: Pharmacological manipulation of the anal sphincter is hampered by a lack of specificity. This study aimed to determine differences in the role of intracellular and extracellular calcium in the development of tone and agonist-induced contractions between internal anal sphincter (IAS) and rectal circular muscle which might allow targeted manipulation. METHODS: Smooth muscle strips from the IAS and rectal circular muscle of 24 Large White pigs were mounted for isometric tension recording in a superfusion organ bath in the presence of different perfusates. RESULTS: IAS developed tone and spontaneous activity that were abolished by nifedipine, which also reduced contractions to noradrenaline to 72 per cent of control values. Rectal smooth muscle developed spontaneous activity but no tone. Nifedipine abolished the activity and reduced contractions to carbachol to 17 per cent of control. Contractile activity was abolished in both tissues in calcium-free solution. Transient exposure to a high calcium concentration reloaded the stores, and the ability of agonists to release stored calcium was tested after 3 min in calcium-free solution. In IAS, noradrenaline contraction was 76 per cent of control and in rectal circular muscle carbachol contraction was 57 per cent of control. Store loading was prevented by nifedipine in rectal smooth muscle but not IAS. Cyclopiazonic acid reduced store filling in both tissues. CONCLUSION: Agonist-induced contraction of IAS is largely due to release of stored calcium and L-type calcium channels are not needed for store filling. Rectal circular smooth muscle depends more on extracellular calcium and uses L-type calcium channels for agonist-induced contraction and store filling. These differences suggest that targeted manipulation may be possible in patients with anorectal disorders.

Adrenergic alpha-Antagonists↗
PubMed1999

Elastic fibres in the vesicourethral junction and urethra of the guinea pig: quantification with computerised image analysis.

Elastic fibres, which are intimately associated with collagen, a major component of the urethra, have been assumed to contribute to the resting urethral closure pressure. The Miller stain for elastin was used to demonstrate elastic fibres in cryostat sections of guinea pig bladder base, vesicourethral junction (VUJ) and urethra. Computerised image analysis was employed to objectively quantify these fibres. Both male and female guinea pigs showed significantly greater amounts of circularly disposed elastic fibres in the VUJ than in the other 2 regions examined. This particular disposition of fibres may be responsible for imparting resiliency and plasticity to the VUJ, allowing it to distend and recoil repeatedly in response to urine outflow. Furthermore, the elastic fibres may be partly responsible for the passive occlusive force in this region. Elastic fibres in the distal urethra were not quantified because of their relative paucity. Sagittal sections of the urethra revealed a mass of longitudinally arranged elastic fibres localised almost exclusively within the mucosa, submucosa and longitudinal smooth muscle layer. Functionally, this arrangement may exist to facilitate urethral length changes that occur in micturition.

Animals↗
PubMed1999

The physiology of the mammalian urinary outflow tract.

Urinary outflow from the mammalian bladder occurs through the urethra. This outflow tract is a complicated structure composed of striated and smooth muscle and vascular urothelium. It is controlled by somatic and autonomic nerves and has several functions: it generates sustained tone to prevent urinary leakage during bladder filling; it generates transient reflex increases in pressure to prevent opening of the lumen when abdominal pressure rises; it undergoes relaxation preceding micturition and can generate urethral opening and shortening during micturition. A urethral pressure profile shows a peak pressure of > or = 100 cmH2O. The outermost coat is striated muscle, the striated or external sphincter. The fibres are predominantly circularly oriented. The extent varies in different species and between sexes. In the human female it extends the length of the urethra, and is composed mainly of slow twitch fibres. In the male, the sphincter extends from the membranous urethra over the base of the prostate and has nearly equal numbers of slow and fast twitch fibres. In both sexes, the posterior border may be deficient in striated muscle, and filled by circularly oriented smooth muscle. Activity in the slow twitch fibres through somatic nerves may be continuous during bladder filling. Outer circular and inner longitudinal smooth muscle is present Strips from either layer will generate sustained tone particularly if dissected from the high pressure zone. This tone is myogenic, and may be achieved in the absence of action potentials, but relies on influx of calcium through L-type calcium channels. Both layers receive sympathetic and parasympathetic excitatory innervation and nitrergic inhibitory innervation. Normal urethral pressure requires blood flow to the urothelium (lamina propria). Striated and smooth muscles are both thought to contribute to the resting urethral pressure in the human. The precise role of the smooth muscles during micturition is as yet unresolved.

Animals↗
PubMed1999

alpha1-adrenoceptors in urethral function.

The external urethral sphincteric mechanism generates forces which seal the urethra and can be measured as urethral pressure. Resting pressure can be augmented transiently through a reflex pathway during increases in intra-abdominal pressure. The exact role of the various components of the urethral wall that generate this pressure is so far unknown. Urethral contributions to continence come from the mucosal hermetic seal, the submucosa and its vascular filling and the smooth and striated muscle. In humans alpha1-adrenoceptor antagonists can reduce urethral pressure, whereas agonists have little effect. A significant part of urethral resting tone is thought to be mediated through the smooth muscles. In vitro, longitudinal and circular smooth muscle components possess spontaneous tone and are innervated by excitatory and inhibitory nerves. Both types possess alpha1-adrenoceptors and contract on stimulation of intrinsic sympathetic nerves or application of alpha1-adrenoceptor agonists. In human urethra, longitudinal smooth muscle predominates but its functional role is unclear. alpha1 stimulation may also affect the vasculature of the submucosa, the striated muscle of the urethra or transmitter release from neurones in the control pathways. Insufficient knowledge of alpha1-adrenoceptor distribution and function within the urethra and the surrounding tissues currently prevents accurate prediction of the therapeutic potential of alpha1-adrenoceptor ligands.

Animals↗
PubMed1999

Co-localization of carbon monoxide and nitric oxide synthesizing enzymes in the human urethral sphincter.

PURPOSE: Ineffective relaxation of the urethral sphincter during micturition can result in obstructive voiding symptoms. Several studies suggest carbon monoxide (CO) acts alongside nitric oxide (NO) as an inhibitory neurotransmitter, and may regulate NO production. We have investigated the distribution of the constitutive CO producing enzyme, heme oxygenase-2 (HO-2) and the NO producing enzyme, neuronal nitric oxide synthase (nNOS), in the human urethra. MATERIALS AND METHODS: Transverse cryostat sections (12 microns.) were cut from three male membranous and six female urethrae. Double immunofluorescence was carried out for co-localization of HO-2 with nNOS using standard methodology. RESULTS: Nerve trunks showing both HO-2 and nNOS immunoreactivities were identified in the urethrae in both sexes. In the female urethrae, of 152 ganglionic cell bodies expressing HO-2 or nNOS immunoreactivity, 74.3% exhibited both HO-2 and nNOS immunoreactivities, 25% exhibited only HO-2 immunoreactivity and 0.7% exhibited only nNOS immunoreactivity. CONCLUSIONS: Immunoreactivity for HO-2 has been demonstrated in neuronal structures innervating the male and female urethral sphincters. The dual expression of HO-2 with nNOS immunoreactivity in cell bodies and nerves suggests that there is an interaction between the CO and NO generating systems. Abnormality in these systems may play a role in urethral dysfunction.

Carbon Monoxide↗
PubMed1999

Blood supply to the bladder during filling.

Amongst other features of bladder physiology, the mechanics of cyclic filling and emptying make the blood supply of the bladder unique with respect to other organs of the body. Blood vessels are required to lengthen and shorten, whilst maintaining sufficient perfusion of the smooth muscle. Interruption of the blood supply may result in ischaemia and, ultimately reperfusion, resulting in bladder pathologies. The blood flow is also likely to be affected by factors such as increased intra-abdominal pressure. In this article, several features of the blood supply to the bladder- and also the urethra--are discussed.

Animals↗
PubMed1998

Purinoceptor subtypes mediating contraction and relaxation of marmoset urinary bladder smooth muscle.

1. The effects of adenosine triphosphate (ATP), adenosine diphosphate (ADP), alpha,beta-methylene-ATP (alpha,beta-MeATP) and 2-methylthio-ATP (2-MeSATP) on longitudinally orientated smooth muscle strips from marmoset urinary bladder were investigated by use of standard organ bath techniques. 2. After being mounted in superfusion organ baths, 66.7% (n=249) of marmoset detrusor smooth muscle strips developed spontaneous tone, 48.2% of all strips examined developed tone equivalent to greater than 0.1 g mg(-1) of tissue and were subsequently utilized in the present investigation. 3. On exposure to ATP, muscle strips exhibited a biphasic response, a rapid and transient contraction followed by a more prolonged relaxation. Both responses were found to be concentration-dependent. ADP and 2-MeSATP elicited a similar response (contraction followed by relaxation), whereas application of alpha,beta-MeATP only produced a contraction. The potency order for each effect was alpha,beta-MeATP> >2-MeSATP> ATP>ADP (contractile response) and ATP=2-MeSATP> or = ADP> > alpha,beta-MeATP (relaxational response). 4. Desensitization with alpha,beta-MeATP (10 microM) abolished the contractile phase of the response to ATP, but had no effect on the level of relaxation evoked by this agonist. On the other hand, the G-protein inactivator, GDPbetaS (100 microM) abolished only the relaxation response to ATP. Suramin (general P2 antagonist, 100 microM) shifted both the contractile and relaxation ATP concentration-response curves to the right, whereas cibacron blue (P2Y antagonist, 10 microM) only antagonized the relaxation response to ATP. In contrast, the adenosine receptor antagonist, 8-phenyltheophylline (10 microM), had no effect on the relaxation response curve to ATP. 5. Incubation with tetrodotoxin (TTX, 3 microM) or depolarization of the muscle strip with 40 mM K+ Krebs failed to abolish the relaxation to ATP. In addition, neither Nomega-nitro-L-arginine (L-NOARG, 10 microM) nor methylene blue (10 microM) had any effect on the relaxation response curve. However, tos-phe-chloromethylketone (TPCK, 3 microM), an inhibitor of cyclicAMP-dependent protein kinase A (PKA), significantly (P<0.01) shifted the curve for the ATP-induced relaxation to the right. 6. It is proposed that marmoset detrusor smooth muscle contains two receptors for ATP, a classical P2X-type receptor mediating smooth muscle contraction, and a P2Y (G-protein linked) receptor mediating smooth muscle relaxation. The results also indicate that the ATP-evoked relaxation may occur through the activation of cyclicAMP-dependent PKA.

Adenosine Diphosphate↗
PubMed1998

The effects of nifedipine and other calcium antagonists on the glibenclamide-sensitive K+ currents in smooth muscle cells from pig urethra.

1. The effects of nifedipine on both levcromakalim-induced membrane currents and unitary currents in pig proximal urethra were investigated by use of patch-clamp techniques (conventional whole-cell configuration and cell-attached patches). 2. Nifedipine had a voltage-dependent inhibitory effect on voltage-dependent Ba2+ currents at - 50 mV (Ki=30.6 nM). 3. In current-clamp mode, subsequent application of higher concentrations of nifedipine (> or =30 microM) caused a significant depolarization even after the membrane potential had been hyperpolarized to approximately -82 mV by application of 100 microM levcromakalim. 4. The 100 microM levcromakalim-induced inward current (symmetrical 140 mM K+ conditions, -50 mV) was inhibited by additional application of three different types of Ca antagonists (nifedipine, verapamil and diltiazem, all at 100 microM). In contrast, Bay K 8644 (1 microM) possessed no activating effect on the amplitude of this glibenclamide-sensitive current. 5. When 100 microM nifedipine was included in the pipette solution during conventional whole-cell recording at -50 mV, application of levcromakalim (100 microM) caused a significant inward membrane current which was suppressed by 5 microM glibenclamide. On the other hand, inclusion of 5 microM glibenclamide in the pipette solution prevented levcromakalim from inducing an inward membrane current. 6. The levcromakalim-induced K+ channel openings in cell-attached configuration were suppressed by subsequent application of 5 microM glibenclamide but not of 100 microM nifedipine. 7. These results suggest that in pig proximal urethra, nifedipine inhibits the glibenclamide-sensitive 43 pS K+ channel activity mainly through extracellular blocking actions on the K+ channel itself.

Animals↗