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Biomedical subjects

Alison F Brading

Publications and source records attributed to Alison F Brading.

31 records · Page 2Linked to original sources
PubMed2003

Ionic basis for the regulation of spontaneous excitation in detrusor smooth muscle cells of the guinea-pig urinary bladder.

(1) The regulatory mechanisms of spontaneous excitation in detrusor smooth muscles of the guinea-pig urinary bladder were investigated using intracellular microelectrode and muscle tension recording techniques. (2) Detrusor smooth muscle cells exhibited nifedipine-sensitive spontaneous action potentials. Their frequency was highly sensitive to membrane polarization and was reduced by lowering the temperature. Lowering the temperature also reduced the frequency of spontaneous contractions and increased their amplitude. (3) Charybdotoxin (50 nm) and iberiotoxin (0.1 microm) increased the amplitude and duration of action potentials, and abolished after hyperpolarizations (AHPs). Both agents also increased the amplitude and duration of spontaneous contractions, and reduced their frequency. Apamin (0.1 microm) did not change the shape of action potentials but often converted individual action potentials into bursts. It also increased the amplitude and duration of spontaneous contractions, and reduced their frequency. 4-aminopyrideine (4-AP, 1 mm) increased the frequency of action potentials without affecting their shape, and increased the amplitude and frequency of spontaneous contractions. (4) Cyclopiazonic acid (CPA, 10 microm) and ryanodine (50 microm) increased the amplitude of action potentials, and suppressed AHPs. Both agents also increased the amplitude and duration of spontaneous contractions, and reduced their frequency. 1,2-(Bis (2-aminophenoxy) ethane-N,N,N', N'-tetraacetic acid tetrakis (acetoxymethyl ester) (50 microm) dramatically increased the amplitude and duration of the action potential, and abolished AHPs. (5) Spontaneous action potentials in detrusor smooth muscles cells result from the opening of L-type Ca2+ channels, and their frequency is regulated by voltage-dependent mechanisms and by some metabolic process. Both the activation of large conductance Ca2+-activated K+ (BK) channels and Ca2+-mediated inactivation of the Ca2+ channels are involved in the repolarizing phase of action potentials. The Ca2+ influx through L-type Ca2+ channels triggers calcium-induced calcium release via ryanodine receptors and activates BK channels to generate AHPs. Both small conductance Ca2+-activated K+ channels and voltage-sensitive K+ channels may contribute to the resting membrane potential and regulate the frequency of action potentials. The regulatory mechanisms of action potentials are closely related to the regulation of spontaneous contractions.

Action Potentials↗
PubMed2003

Electrical properties of detrusor smooth muscles from the pig and human urinary bladder.

(1) The electrophysiological properties of detrusor smooth muscles have been studied almost exclusively in small mammals and the relevance of the information to the human bladder has been questioned. In the present study, electrical properties of detrusor smooth muscles of the pig and human were investigated using intracellular recording techniques. (2) Bladder smooth muscles of the pig and human exhibited nifedipine (10 microm)-sensitive spontaneous action potentials, and their frequency was highly sensitive to membrane polarization. (3) During bursts of action potentials, each action potential was followed by a fast after-hyperpolarization (fast AHP). Charybdotoxin (CTX, 50 nm) increased the amplitude and duration of action potentials but failed to inhibit the fast AHPs, while apamin (0.1 microm) blocked the fast AHPs and induced action potential complexes, which were followed by slow AHPs. 4-Aminopyridine (4-AP, 1 mm) suppressed the slow AHP and increased action potential frequency. (4) In the human bladder, transmural stimuli initiated inhibitory junction potential-like hyperpolarizations, which were followed by action potential discharges. The hyperpolarizations were blocked by atropine (1 microm) and by apamin (0.1 microm) but not by CTX (50 nm). In the pig bladder, transmural stimuli evoked excitatory junction potentials (EJPs), which triggered action potentials. After desensitizing P2x receptors with alpha,beta methylene-ATP (10 microm), nerve-evoked responses were similar to those of human bladder. (5) These results indicate that detrusor smooth muscles of the pig share many features of electrical properties with those of the human. In addition to large conductance (BK) and small conductance (SK) Ca2+-activated K+ channels, voltage-dependent K+ (VK) channels may play an important role in the regulation of electrical activity of detrusor smooth muscles.

Action Potentials↗
PubMed2003

Preconditioning protects the guinea-pig urinary bladder against ischaemic conditions in vitro.

AIMS: To investigate the ability of ischaemic preconditioning (IPC) to protect guinea-pig detrusor from damage caused by a subsequent more prolonged exposure to ischaemic conditions. MATERIALS AND METHODS: Smooth muscle strips were mounted for tension recording in small organ baths continuously superfused with Krebs' solution at 37 degrees C. Ischaemia was mimicked by removing oxygen and glucose from the superfusing solution. Contractile responses to electrical field stimulation (EFS) and carbachol were monitored. Three regimes of preconditioning were examined: 15, 10, and 5 min of ischaemic conditions followed by 15, 10, and 5 min of normal conditions, respectively. RESULTS: Without preconditioning, nerve-mediated responses were significantly and proportionally reduced by periods of ischaemic conditions lasting for 45, 60, and 90 min, but recovered fully after exposure to ischaemic conditions for 30 min. The recovery of the responses to EFS was significantly improved in preconditioned strips when the period of ischaemic conditions was 45 or 60 min. However, no significant differences were seen with preconditioning when the period of ischaemic conditions was 90 min. The recovery of responses to carbachol was much greater than for the responses to EFS, and no significant differences were found between control and preconditioned strips. CONCLUSIONS: It is suggested that in vivo short periods of transient ischaemia may be able to protect the guinea-pig bladder from the impairment associated with longer periods of ischaemia and reperfusion, which might happen in obstructed micturition. Our results also indicate that the phenomenon affects mainly the intrinsic nerves, which are more susceptible to ischaemic damage than the smooth muscle.

Animals↗
PubMed2003

Role of nitric oxide in anorectal function of normal and neuronal nitric oxide synthase knockout mice: a novel approach to anorectal disease.

PURPOSE: In vitro data suggest that nitric oxide is an important inhibitory neurotransmitter in the internal anal sphincter, and morphologic evidence implies that it mediates the rectoanal inhibitory reflex. This study examined the anatomy, physiology, and pharmacology of the internal sphincter in control and neuronal nitric oxide synthase knockout mice. METHODS: Neuronal nitric oxide synthase, nicotinamide adenosine triphosphate dinucleotide phosphate diaphorase histochemistry, and PGP 9.5 immunohistochemistry were compared between knockout and sibling control mice. Anorectal manometry was performed with a balloon-tipped water-perfused catheter. In vitro studies were performed on both whole internal anal sphincter rings and strips. RESULTS: Staining of the myenteric plexus and nerves traversing the internal anal sphincter in sibling control mice demonstrated the presence of neuronal nitric oxide synthase and nicotinamide adenine dinucleotide phosphate diaphorase at these sites. These markers were absent in knockout mice. Maximum anal resting pressure was similar in control and knockout mice (15.6 +/- 2.6 cm H(2)O (n = 4) vs. 14.0 +/- 2.3 cm H(2)O (n = 7)). The rectoanal inhibitory reflex was present in all control mice (n = 4) but in only four of seven knockout mice. Field stimulation with parameters designed to activate inhibitory nerves produced relaxation of internal sphincter tissue from both control and knockout mice, which was partially attenuated in control mice only by pretreatment with the nitric oxide synthase inhibitor N omega-nitro-L-arginine. Further inhibition of nerve-induced relaxation in control mice was achieved with antagonists of vasoactive intestinal peptide, adenosine triphosphate, and heme oxygenase. CONCLUSIONS: Although in the normal mouse, nitric oxide is an inhibitory neurotransmitter in the internal sphincter, other transmitters may play a role in the rectoanal inhibitory reflex. These other inhibitory neurotransmitters can apparently compensate for the absence of nitric oxide synthase in knockout mice to maintain approximately normal function.

Anal Canal↗
PubMed2003

Nerve regeneration: might this be the only solution for functional problems of the urinary tract?

PURPOSE OF REVIEW: To assess the potential role of nerve regeneration in restoring urinary tract function, the rapidly developing and exciting area of central and peripheral nerve repair and regeneration is reviewed, with particular reference to papers in which animal models of nerve damage resulting in urogenital dysfunction have been used. The difficulties and potential of these techniques for therapeutic application to human subjects with functional problems of the urinary tract are discussed. RECENT FINDINGS: Methods for encouraging regeneration of cut axons and directed growth in the inhibitory environment of the central nervous system are being extensively explored. The recent discovery of the potential of olfactory ensheathing cells has proved a significant advance. Olfactory ensheathing cells are a type of glial cell which can be harvested from the olfactory mucosa. Transplantation of these cells, in conjunction with a biodegradable synthetic nerve guide or conduit, has been shown to restore urinary tract function after spinal cord injury. Artificial, biodegradable conduits have also restored bladder and spermatic duct function after sympathetic nerve damage. Other adjuvants facilitating the process of axonal recovery include the use of neurotrophins to accelerate and guide the formation of new nerve-fibre growth. SUMMARY: These revolutionary technologies may, in the future, provide a means of treating urinary tract dysfunction with some types of aetiology, including acute spinal cord injury, and injury to nerves following pelvic surgery. It is, however, less likely that these treatments will be used successfully in the near future in patients in which the neural damage is long term, or associated with death of post-ganglionic neurons.

Animals↗
PubMed2003

Morphology, phenotype and ultrastructure of fibroblastic cells from normal and neuropathic human detrusor: absence of myofibroblast characteristics.

PURPOSE: Fibroblasts are functionally diverse and fibroblastic cells with smooth muscle-like characteristics (myofibroblasts) regulate smooth muscle activity in certain tissues. The presence of myofibroblasts has been reported in the bladder with important implications for normal function and detrusor overactivity. We assessed fibroblastic cell characteristics to discern features suggesting a myofibroblast phenotype in normal or neuropathic human detrusor. MATERIALS AND METHODS: A total of 25 control samples were obtained from cadaveric organ donors or patients with a mean age of 42.3 years investigated for hematuria and compared with samples from 18 patients with a mean age of 37.4 years with neurogenic detrusor overactivity. Morphology, phenotypic expression of various markers and the ultrastructure of each fibroblastic cell visible in multiple sections from each specimen was evaluated by 2 independent assessors. RESULTS: Fibroblastic cells were observed throughout the smooth muscle and connective tissue. They were located peripherally on muscle fascicles and had a polar stellate appearance with processes ramifying in interfascicular planes and muscle. They possessed vimentin-like immunoreactivity and weak c-kit-like immunoreactivity but not desmin or alpha-smooth muscle actin-like immunoreactivity. Ultrastructurally they showed dilated rough endoplasmic reticulum with a moderately electron dense amorphous content and prominent golgi complexes. Nuclei had clumped peripheral heterochromatin. There were extensive flattened processes that lacked basal laminae. There was no specific contact with nerve fibers or smooth muscle. Neuropathic bladder samples did not differ overtly from those of controls. CONCLUSIONS: The detrusor possesses an extensive network of fibroblastic cells and processes. No evidence of myofibroblast differentiation was discerned in normal or neuropathic detrusor, although a minority subpopulation or regional variability in cellular phenotype could not be excluded.

Adult↗
PubMed2003

Expression of nitric oxide synthase immunoreactivity in the human female intramural striated urethral sphincter.

PURPOSE: While we have recently detected neuronal nitric oxide synthase (nNOS) immunoreactivity in a heterogeneous population of human male urethral striated muscle, to our knowledge the association of nNOS in the female counterpart is unknown. We investigated the association of nNOS with female urethral striated muscle and re-investigated muscle fiber types. MATERIALS AND METHODS: Cryostat sections were taken from the middle third of 4 human female urethras. Nicotinamide adenine dinucleotide phosphate diaphorase histochemistry and nNOS immunohistochemistry were performed. Muscle fiber types were identified by myofibrillar adenosine triphosphatase histochemistry and fast twitch troponin T immunohistochemistry. The association between nNOS immunoreactivity and muscle fiber type was analyzed. RESULTS: Positive staining for nicotinamide adenine dinucleotide phosphate diaphorase histochemistry and nNOS immunoreactivity were recognized in the sarcolemma of 43.9% of female urethral striated muscle fibers. Immunoreactivity for fast twitch troponin T immunohistochemistry was demonstrated by 2% of the striated fibers. The use of myofibrillar adenosine triphosphatase showed that all fibers darkly stained uniformly at a pH of 9.6, 4.6 and 4.3, suggesting that they were myofibrillar intermediate muscle fibers. The results allowed the differentiation of 2 subgroups of fibers, namely smaller fibers (modal diameter 10.1 to 15.0 microm.) without nNOS immunoreactivity and larger fibers (modal diameter 15.1 to 20.0 microm.) with nNOS immunoreactivity. CONCLUSIONS: To our knowledge female urethral striated muscle has for the first time been found to consist of myofibrillar intermediate fibers and nNOS was positively localized in the sarcolemma of a subgroup of the fibers. This study provides a basis for further investigation into female urethral striated sphincter function and changes in pathological conditions.

Adenosine Triphosphatases↗
PubMed2002

Modification of ATP-sensitive K+ channels by proteolysis in smooth muscle cells from pig urethra.

Patch-clamp experiments have been performed to investigate the effects of endoproteases (such as trypsin, carboxypeptidase B) on both membrane currents and unitary currents in isolated smooth muscle cells from pig proximal urethra (conventional whole-cell configuration, cell-attached configuration, and inside-out patches). Application of either trypsin (1 mg/mL) or carboxypeptidase B (0.1 mg/mL) to the intracellular surface of the excised membrane patches stimulated the activity of a 2.1 pA K+ channel (in symmetrical 140 mM K+ conditions) at a holding potential of -50 mV. The trypsin-induced K+ channels in inside-out configuration exhibited the same amplitude and similar channel opening kinetics to the levcromakalim-induced ATP-sensitive K+ channel (i.e. K ATP channel) in cell-attached patches of the same membrane; however, the sensitivity of the channels to glibenclamide was greatly reduced after the trypsin-treatment. The activity of the trypsin-induced K+ channel was reversibly inhibited by cibenzoline in an inside-out configuration (Ki = 5 microM). It is concluded that trypsin and carboxypeptidase B reactivate the channel with an intact pore activity but the different pharmacological properties of the channels may reflect some change in the conformation in channel proteins after proteolysis.

ATP-Binding Cassette Transporters↗
PubMed2002

Ca(2+) channel properties in smooth muscle cells of the urinary bladder from pig and human.

Ca(2+) channel properties of pig and human bladder smooth muscle were investigated utilizing standard whole-cell patch clamp techniques. Both the amplitude obtained and the current density of Ca(2+) channel current evoked by step depolarization were larger in human than in pig myocytes. The inward currents were sensitive to an L-type Ca(2+) channel antagonist, nifedipine, the effects of which were not significantly different between species. In both species, prior application of ATP (0.1 mM) had no effect on activation of this voltage-sensitive channel current, while a muscarinic receptor agonist, carbachol (0.1 mM), significantly attenuated the amplitude of this current. Furthermore, inclusion of GDP-beta-S or Heparin in the pipette abolished or had no effect on the suppression of Ca(2+) current by carbachol, respectively. These results forward the pig as a good model for the human in detrusor Ca(2+) channel properties, especially with regard to neural modulation, although voltage-sensitive Ca(2+) channels seem to make greater contribution in human bladder physiology.

Adenosine Triphosphate↗
PubMed2002

Phosphodiesterase inhibitors cause relaxation of the internal anal sphincter in vitro.

PURPOSE: Pharmacologic treatments are gaining widespread acceptance as first-line therapy for anal fissure. However, existing treatments have limited clinical usefulness because of side effects and incomplete healing rates. METHODS: Fresh human surgical resection specimens containing internal anal sphincter and rectal circular muscle were collected. Strips of smooth muscle were cut from each muscle group and mounted in a superfusion organ bath. The effects of increasing concentrations of phosphodiesterase inhibitors were evaluated. RESULTS: All phosphodiesterase inhibitors tested caused a dose-dependent reduction in the tone of the internal anal sphincter, with potencies as follows: vinpocentine (phosphodiesterase-1 inhibitor; 50 percent maximum inhibition concentration = 0.87 +/- 0.10 microM), erythro-9-(2-hydroxy-3-nonyl) adenine hydrochloride (phosphodiesterase-2 inhibitor; 32 +/- 4.8 microM), trequinsin (phosphodiesterase-3 inhibitor; 0.28 +/- 0.041 microM), rolipram (phosphodiesterase-4 inhibitor; 63 +/- 9 microM), zaprinast (phosphodiesterase-1,5,6,9,11 inhibitor; 3 +/- 0.69 microM), and dipyridamole (phosphodiesterase-5,6,8,10,11 inhibitor; 5.5 +/- 2 microM). Although all inhibitors were also effective on rectal circular muscle strips, erythro-9-(2-hydroxy-3-nonyl) adenine hydrochloride, trequinsin, and rolipram were at least an order of magnitude more potent in this tissue than in the internal anal sphincter. CONCLUSIONS: There are several functionally important phosphodiesterases in the internal anal sphincter and rectal circular muscle. Both adenosine 3', 5'-cyclic monophosphate and guanosine 3',5'-cyclic monophosphate appear to be important in the myogenic tone of the internal anal sphincter, and this study provides further evidence of the sphincteric specialization of this tissue. Phosphodiesterase inhibitors might represent a new therapy for the treatment of anal fissure.

Adenine↗
PubMed2002

The physiology, pharmacology and therapeutic manipulation of the internal anal sphincter.

Recent research into the physiology and pharmacology of the internal anal sphincter has elucidated the importance of this structure in health and disease. Its pharmacological manipulation for therapeutic gain has focused mainly on agents to reduce internal anal sphincter tone, a 'chemical sphincterotomy' that might heal chronic anal fissure. However, drugs to increase sphincter tone, and augment intermittent and appropriate relaxation are also being evaluated. The initial results with this medical approach to anorectal disease have often been disappointing, failing to match the results achievable with surgery, and many of these drugs have a high rate of side effects in the short term. However, clinical trials have yet to establish the optimum doses, dose intervals and routes of administration for many of these therapies. Furthermore, it is uncertain whether this medical approach should be applied to all patients or just to an as yet undefined subgroup. Certainly, even in the current environment of uncertainty, there is little reason not to try medical manipulation of the internal sphincter as first-line treatment. Surgery remains an option for treatment failures; patients responding to pharmacological manipulation of the internal anal sphincter are spared the long term risks of continence that are inherent in many surgical procedures on the anorectum.

Anal Canal↗