Modulation by stereoselective inhibition of cyclo-oxygenase of electromechanical coupling in the guinea-pig isolated renal pelvis

Mediators of human ureteral smooth muscle contraction-a role for erythropoietin, tamsulosin and Gli effectors

Background

Ureteral contractility is a poorly understood process. Contractions have been demonstrated to occur in the smooth muscle layers of the ureter. Previous work suggests the involvement of Gli family proteins and erythropoietin (EPO) in regulating mammalian ureteral smooth muscle contraction. We sought to devise a method by which the effects of these proteins and tamsulosin on distal human ureteral tissue contractility could be investigated to better understand mechanisms regulating human ureteral function.

Methods

IRB approval was obtained to procure portions of extraneous distal ureteral tissue from living donor renal transplants. Contractility was measured by placing the tissue in Krebs buffer and stimulating via a uniform electric current. Contractile force was recorded with each stimulation with and without the presence of a Gli inhibitor (GANT61) or EPO. Each ureteral specimen was subsequently fixed and tested by immunohistochemistry to determine Gli, EPO and alpha-adrenergic receptor activity.

Results

Electrical field stimulation successfully elicited contractions in the ureteral tissue. Administering tamsulosin decreased force and duration of ureteral contractions. Inhibiting Gli signaling decreased contractility and EPO decreased ureteral contractile forces within 5 minutes of administration versus untreated controls. Staining confirmed Gli1 protein and α-adrenergic receptor expression in ureteral smooth muscle and epithelial tissue with EPO receptor expression confined to the epithelial layer.

Conclusions

Distal ureteral contractile forces are decreased by inhibition of Gli family proteins and the α-adrenergic receptor. EPO acts within five minutes, suggesting ion channel involvement instead of changes in gene expression. Continuing work will elucidate the role of these proteins in coordinating ureteral contractions. This has implications for the use of pharmacologic methods to address ureteral contractility and dysfunctional peristalsis during stone passage, ureteroscopy, in transplant patients and potentially to reduce symptoms from ureteral stents.

Prostaglandin D2 effects and DP1 /DP2 receptor distribution in guinea pig urinary bladder out-flow region

The proximal urethra and urinary bladder trigone play important roles in continence. We have previously shown that PGD₂ is released from guinea pig bladder urothelium/suburothelium and can inhibit detrusor contractile responses. We presently wished to investigate PGD₂ actions in guinea pig out‐flow region and the distribution of DP₁/DP₂ receptors. The effects of PGD₂ on urothelium‐intact trigone and proximal urethra contractility were studied in organ bath experiments. Expression of DP₁/DP₂ receptor proteins was analysed by western blot. Immunohistochemistry was used to identify distribution of DP₁/DP₂ receptors. PGD₂ in a dose‐dependent manner inhibited trigone contractions induced by electrical field stimulation (EFS) and inhibited spontaneous contractions of the proximal urethra. PGD₂ was equally (trigone) or slightly less potent (urethra) compared with PGE₂. Expression of DP₁ and DP₂ receptors was found in male guinea pig bladder trigone, neck and proximal urethra. In the trigone and proximal urethra, DP₁ receptors were found on the membrane of smooth muscle cells and weak immunoreactivty was observed in the urothelium. DP₂ receptors were distributed more widespread, weakly and evenly in the urothelium and smooth muscles. Inhibitory effects by PGD₂ on motor activity of guinea pig trigone and proximal urethra are consistent with finding DP₁ and DP₂ receptors located in the urothelium and smooth muscle cells of the trigone and proximal urethra, and PGD₂ may therefore be a modulator of the bladder out‐flow region, possibly having a function in regulation of micturition and a role in overactive bladder syndrome.

Electrical propagation in the renal pelvis, ureter and bladder

Under normal conditions, following the passage of urine from the collecting duct, the urine is stored briefly in the renal pelvis before being transported through the ureter to the bladder where the urine is stored for a longer time (hours) before being voided through the urethra. The transport of urine from the renal pelvis to the bladder occurs spontaneously due to contractions of the muscles in the wall of the pelvis and ureter. Spontaneous contractions also occur in the detrusor muscle and are responsible for maintaining the bladder shape during the filling phase. These muscle contractions occur as result of electrical impulses, which are generated and propagated through different parts of the urinary tract. The renal pelvis and the ureter differ from the bladder in relation to the origin, characteristics and propagation of these electrical impulses. In the ureter, the electrical impulses originate mainly at the proximal region of the renal pelvis and are transmitted antegradely down the length of the ureter. The electrical impulses in the bladder, on the other hand, originate at any location in the bladder wall and can be transmitted in different directions with the axial direction being the prominent one. In this manuscript, an overview of the current state of research on the origin and propagation characteristics of these electrical impulses in the normal and pathological conditions is provided.

Propagation characteristics of the electrical impulse in the normal and obstructed ureter as determined at high electrophysiological resolution

OBJECTIVE

To investigate the propagation of the electrical impulses in a unilateral ureteric obstruction model using a high-resolution technique in vivo.

MATERIALS AND METHODS

In Wistar rats (n= 15), the left mid-ureter was occluded and the electrical activity was recorded from the proximal and distal part of the obstructed ureter and from the right ureter at different times up to 2 weeks post-obstruction using 64 extracellular electrodes.

RESULTS

In the left ureter, impulses propagated in an antegrade direction at a frequency of 15.5 ± 1.3/min and a velocity of 1.6 ± 0.1 cm/s. Immediately post-obstruction, the proximal part showed an increase in frequency (19.1 ± 2.5/min; P < 0.05) followed by a gradual decrease (at 2 weeks: 2.5 ± 1.2/min; P < 0.001). The velocity of these impulses decreased gradually (at 2 weeks: 0.5 ± 0.1 cm/s; P < 0.05). Distally, the antegrade propagations gradually disappeared and, at 1 week, 33% of ureters showed retrograde impulses and 67% displayed no electrical activity. The frequency of both antegrade and retrograde impulses distal to the obstruction dropped immediately after obstruction so that, at 1 day, it was 1.0 ± 0.3 and 1.5 ± 0.2/min, respectively (P < 0.01 for both). The velocity of these antegrade and retrograde impulses showed a significant rise throughout the post-obstruction period. The right ureter showed only a transient increase in frequency from 18.7 ± 2.7 to 30.3 ± 6.1/min (P < 0.05).

CONCLUSIONS

Using this high-resolution technique, it is concluded that, after ureteric obstruction, there were immediate and significant changes in the propagation of electrical impulses in the proximal and distal left ureter and in the right ureter, all of which behaved differently. This data may provide a better insight into the electrophysiological function of the normal and obstructed ureter.

Effects of a non-selective COX inhibitor and selective COX-2 inhibitors on contractility of human and porcine ureters in vitro and in vivo

BACKGROUND AND PURPOSE

Anti-inflammatory drugs are used in the treatment of acute renal colic. The aim of this study was to investigate the effects of selective COX-2 inhibitors and the non-selective COX inhibitor diclofenac on contractility of human and porcine ureters in vitro and in vivo, respectively. COX-1 and COX-2 receptors were identified in human ureter and kidney.

EXPERIMENTAL APPROACH

Human ureter samples were used alongside an in vivo pig model with or without partial ureteral obstruction. COX-1 and COX-2 receptors were located in human ureters by immunohistochemistry.

KEY RESULTS

Diclofenac and valdecoxib significantly decreased the amplitude of electrically-stimulated contractions in human ureters in vitro, the maximal effect (Vmax) being 120 and 14%, respectively. Valdecoxib was more potent in proximal specimens of human ureter (EC50=7.3 x 10(-11) M) than in distal specimens (EC50=7.4 x 10(-10) M), and the Vmax was more marked in distal specimens (22.5%) than in proximal specimens (8.0%) in vitro. In the in vivo pig model, parecoxib, when compared to the effect of its solvent, significantly decreased the maximal amplitude of contractions (Amax) in non-obstructed ureters but not in obstructed ureters. Diclofenac had no effect on spontaneous contractions of porcine ureter in vivo. COX-1 and COX-2 receptors were found to be expressed in proximal and distal human ureter and in tubulus epithelia of the kidney.

CONCLUSIONS AND IMPLICATIONS

Selective COX-2 inhibitors decrease the contractility of non-obstructed, but not obstructed, ureters of the pig in vivo, but have a minimal effect on electrically-induced contractions of human ureters in vitro.

Clozapine bioactivation induces dose-dependent, drug-specific toxicity of human bone marrow stromal cells: A potential in vitro system for the study of agranulocytosis

Clozapine, an atypical antipsychotic drug effective in treatment of refractory schizophrenia causes potentially life-threatening agranulocytosis. The drug undergoes bioactivation to a toxic, chemically reactive intermediate with capacity to target stromal cells, central components of the bone marrow microenvironment implicated in neutrophil development. To identify possible mechanisms underpinning disruption of stroma as a site of drug bioactivation, toxicity was induced in vitro. Therefore metabolite generation procedures utilizing HOCl or HRP-H(2)O(2) as primary components involved in clozapine metabolism were adapted for stromal culture and coupled with viability determinations. Drug oxidation by HOCl was less toxic to stromal cells than HRP-H(2)O(2) based methods. More specifically, clozapine bioactivation by HRP-H(2)O(2) caused dose-dependent inhibition of stromal viability at therapeutically relevant concentrations. Differences in susceptibility of HAS303 and LP101 cells to the clozapine nitrenium ion were also evident. Stromal cell death was attributed to clozapine in the presence of a complete metabolising system comprising HRP and H(2)O(2). In the absence of a complete metabolising system clozapine was not cytotoxic. For LP101 cells, drug plus HRP (minus H(2)O(2)) also induced toxicity. Importantly, other antipsychotic drugs including risperidone, olanzapine and haloperidol when bioactivated, were not cytotoxic, indicating system specificity for clozapine. Exogenous GSH, N-acetylcysteine, l-ascorbic acid, catalase, and sodium azide afforded protection to cells whereas S-methylGSH, GSSG, ketoprofen and proadifen did not. Thus functional data derived from the in vitro stromal system defined in these studies may enable further investigation of the mechanisms subserving stromal impairment in clozapine-induced agranulocytosis and direct attention to improved methods for its prevention.

Pacemaker activity in the upper urinary tract

Ureteral peristaltic activity begins with the origin of electrical activity at pacemaker sites. These sites are located in the proximal portion of the urinary collecting system. The 'atypical' smooth muscle cells at these sites fire 'pacemaker' potentials at a frequency higher than the 'driven' action potentials recorded from typical smooth muscle cells. In contrast to typical smooth muscle cells, these atypical pacemaker cells have less than 40% of their cellular area occupied by contractile filaments and demonstrate a sparse immunoreactivity for alpha-smooth muscle actin. Expression of c-Kit, a tyrosine kinase receptor, correlates with the onset of organized ureteral peristalsis in the embryo. Capsaicin-sensitive sensory afferents and the endogenous release of tachykinins and prostaglandins are involved in the maintenance of normal ureteral peristalsis.

Serum-mediated relaxant response to toluene diisocyanate (TDI) in isolated guinea-pig bronchi

The present study was designed to evaluate whether pre-incubation with serum, obtained from both control and toluene diisocyanate (TDI)-immunized guinea-pigs, modified the contractile response to TDI in isolated guinea-pig bronchial rings. Guinea-pigs were anaesthetized and the main bronchi dissected in two rings. Bronchial rings were incubated with normal or immune serum (100 microl ml(-1) for 2 h) and dose-response curves to TDI (0.03-1000 microM) were studied isometrically. Before serum incubation, in eight bronchial rings, epithelium was removed by rubbing the luminal surface gently with a gauze. In control rings, TDI produced a concentration-dependent contraction, whereas in rings pre-incubated with either normal or TDI-immune serum, it produced a concentration-dependent relaxation. Relaxation was 101.4 (SEM 17.4)% and 94.9 (SEM 21)% of the relaxation induced by isoproterenol (1 mM) respectively with normal and TDI-immune serum. Similarly to the pre-incubation with serum, pre-incubation with albumin produced a concentration-dependent relaxation to TDI. Serum-induced relaxant response to TDI was not affected by capsaicin desensitization, it was only partially inhibited by an NK1-tachykinin antagonist, whereas it was blocked by indomethacin. In bronchial rings without epithelium, pre-incubated with serum, TDI caused contraction at highest doses, while it still induced relaxation at the lowest doses. This study shows that one or more components of the serum modify the contractile response to TDI in isolated guinea-pig bronchi. In bronchial rings without epithelium serum was able to inhibit the contration induced by low doses of TDI.

Effects of selective inhibitors of cyclo-oxygenase-1 (COX-1) and cyclo-oxygenase-2 (COX-2) on the spontaneous myogenic contractions in the upper urinary tract of the guinea-pig and rat

The role of cyclo-oxygenase-1 (COX-1) and cyclo-oxygenase-2 (COX-2) in the upper urinary tract of the guinea-pig and rat was examined using simultaneous tension recordings of the proximal and distal regions of the renal pelvis and the ureter. The guinea-pig upper urinary tract contracted at a frequency (7.52+/-0.3 min(-1) at 35 degrees C) significantly lower than the frequency in the proximal renal pelvis (21.6+/-1.3 min(-1)) and in the distal renal pelvis and ureter (20.2+/-1.4 min(-1)) of the rat (at 30 degrees C). Indomethacin (>/=1 microM for 60 min), decreased the motility index (amplitudexfrequency) (MI) in all three regions of the guinea-pig upper urinary tract, an effect which mainly arose from a decrease in the frequency of contractions. In the rat, indomethacin (1 - 30 microM for 60 min) significantly decreased the MI calculated in the proximal renal pelvis (>/=30 microM indomethacin), and in the distal renal pelvis (>/=10 microM indomethacin), arising from a significant decrease in the amplitude of contractions. The COX-1 inhibitor, valeryl salicylate (VSA) (5 - 100 microM for 60 min), had no effect on either the amplitude or frequency of contractions in the guinea-pig upper urinary tract. In contrast, VSA increased the force of contractions in the proximal and distal renal pelvis of the rat, whilst having little effect on the frequency of contractions. The COX-2 inhibitor, NS-398 (10 - 100 nM for 60 min) reduced the MI in the guinea-pig upper urinary tract in a concentration-dependent manner. The MIs calculated for the proximal renal pelvis, distal renal pelvis and ureter, were decreased by 72, 64 and 72% respectively, in 100 nM NS-398. NS-398 (10 - 100 nM) had no effect on any of the three parameters measured in either the proximal or distal renal pelvis of the rat. These data suggest that endogenously-released prostaglandins (PGs) maintain the myogenic contractility of the upper urinary tract in both the guinea-pig and rat. Moreover COX-2 is the primary enzyme involved in synthesizing PGs in the guinea-pig upper urinary tract, while COX-1 appears to be the predominantly active enzyme in the rat.

Electrical basis of peristalsis in the mammalian upper urinary tract

1. Peristalsis in the mammalian upper urinary tract (UUT) is mostly myogenic in origin, originating predominately in the proximal pelvicalyceal regions of the renal pelvis, an area that is enriched with specialized smooth muscle cells termed 'atypical' smooth muscle cells. Propagating peristaltic contractions are little affected by blockers of either autonomic nerve function or nerve impulse propagation; however, blockers of sensory nerve function or prostaglandin synthesis reduce both the frequency and the strength of the spontaneous contractions underlying peristalsis. 2. The electrical drive for these peristaltic contractions has long been considered to involve mechanisms analogous to the heart, such that 'atypical' smooth muscle cells generate spontaneous 'pacemaker' action potentials. These pacemaker potentials trigger the firing of action potentials and contraction in the muscular regions of the renal pelvis, which propagate distally to the ureter, propelling urine towards the bladder. 3. Recent intracellular microelectrode and single cell/channel patch-clamp studies have revealed that the ionic conductances underlying the action potentials recorded in the UUT are likely to involve the opening and slow closure of voltage-activated 'L-type' Ca2+ channels, offset by the time-dependent opening and closure of both voltage- and Ca(2+)-activated K+ channels. 4. In the present review we summarize the current knowledge of the ionic mechanisms underlying action potential discharge in the UUT, as well as present our view on how this electrical activity supports the initiation and conduction of UUT peristalsis.

Effects of metamizol on nociceptive responses to stimulation of the ureter and on ureter motility in anaesthetised rats

In this study, we have examined the effects of metamizol (dipyrone), a non-opioid analgesic which is effective in relieving renal colic pain, on nociceptive responses evoked by stimulation of the ureter, on pyeloureteral motility and on intraureter pressure after ureter obstruction in anaesthetised rats. Metamizol (5- 50 mg/kg i.v.) dose-dependently inhibited reflex pressor responses evoked by distensions of the ureter to pressures of 30, 55 and 75 mmHg for 30 s (ID50 = 8 +/- 1 mg/kg). Metamizol also dose-dependently reduced intraureter pressure during total ureter occlusion (25 mg/kg produced a reduction of 25% in 10 min). However, metamizol at doses up to 50 mg/kg had no effect on pyleoureteric motility (contraction amplitude, rate or intraureter pressure) under normal pressure conditions. We conclude that metamizol has a direct antinociceptive action on pain of ureteric origin, and spasmolytic effects after ureter obstruction (but not under normal conditions) which may also contribute to pain relief.

Stimulation of neuropeptide release from sensory and enteric neurons in the guinea-pig by alpha-latrotoxin

alpha-Latrotoxin, from black widow spider venom, stimulates exocytosis of small synaptic vesicles at central and peripheral synapses. However, it is widely accepted that neuropeptide-containing large dense-core vesicles are insensitive to the toxin. In the present study, we investigated whether alpha-latrotoxin releases neuropeptides from primary afferent and enteric neurons. The guinea-pig renal pelvis is innervated by primary sensory neurons containing tachykinins and calcitonin gene-related peptide, but has no functional cholinergic or noradrenergic motor innervation. alpha-Latrotoxin increased the amplitude of spontaneous myogenic contractions of the renal pelvis, and this effect was prevented by prior capsaicin desensitization and by antagonists at neurokinin-1 and neurokinin-2 receptors. In the presence of the latter antagonists, alpha-latrotoxin decreased the amplitude of the contractions, and this is likely to be mediated by calcitonin gene-related peptide. Thus, alpha-latrotoxin releases tachykinins and calcitonin gene-related peptide from capsaicin-sensitive sensory neurons in the renal pelvis. The circular muscle of the guinea-pig distal colon is innervated by excitatory and inhibitory motor neurons, which use a number of transmitters. In the presence of antagonists to block each of the known transmitters apart from the tachykinins, alpha-latrotoxin increased the amplitude of spontaneous contractions; this effect was prevented by the prior addition of neurokinin-1 and neurokinin-2 receptor antagonists. Thus, alpha-latrotoxin stimulates the release of tachykinins from excitatory motor neurons in the myenteric plexus of the distal colon. In conclusion, this study demonstrates that alpha-latrotoxin is able to evoke the release of neuropeptides from both sensory and enteric neurons. This suggests that exocytosis of large dense-core vesicles shares more of the features of exocytosis of small synaptic vesicles than has previously been appreciated.

CGRP inhibition of electromechanical coupling in the guinea-pig isolated renal pelvis

We aimed at studying the mechanism(s) of the inhibitory effect exerted by calcitonin gene-related peptide (CGRP) on the spontaneous activity of the guinea-pig isolated renal pelvis. In organ bath experiments, CGRP (1-100 nM) produced a concentration-dependent (EC50 8 nM) partial inhibition (Emax about 35% inhibition of motility index) of spontaneous contractions. The potassium (K) channel opener, cromakalim (3-10 microM) promptly suppressed the spontaneous contractions in a glibenclamide-(10 microM) sensitive manner. Glibenclamide (10 microM) did not affect the inhibitory action of CGRP. The calcium (Ca) channel agonist, Bay K 8644 (1 microM), markedly enhanced the spontaneous activity of the renal pelvis and reduced the inhibitory effect of CGRP. The protein kinase A inhibitors Rp-cAMPS (300 microM), H8 (100 microM) and H89 (10 microM), and the blockers of intracellular Ca handling by sarcoplasmic reticulum, ryanodine (100 microM) and thapsigargin (1 microM) did not affect the response to CGRP. The response to CGRP was likewise unaffected by the nitric oxide synthase inhibitor, L-nitroarginine (30 microM) and by the protein kinase G inhibitor, KT5823 (3 microM). Furthermore, the inhibitory action of CGRP was not modified by lowering the extracellular concentration of K (from 5.9 to 1.2 mM) nor by increasing (from 2.5 to 3.75 mM) or decreasing (from 2.5 to 0.25 mM) the extracellular Ca concentration. Replacement of 80% glucose with 2-deoxyglucose (2-DOG) reduced the amplitude of spontaneous contractions, both in the absence and presence of 10 microM glibenclamide. In the presence of 2-DOG, the inhibitory action of CGRP was enhanced at a similar extent, either in the absence or presence of glibenclamide. In sucrose gap, the effect of CGRP (0.1 microM for 5 min) was separately analyzed in the proximal (close to the kidney) and distal (close to the ureter) regions of the renal pelvis. Both preparations discharged spontaneous (pacemaker) action potentials having different shape, duration and frequently. CGRP had no effect on pacemaker potentials in the proximal renal pelvis while producing about 30% reduction of the frequency of pacemaker potentials and motility index in the distal renal pelvis. Cromakalim (3 microM) abolished pacemaker potentials in both regions of the renal pelvis. In conjunction with the results of previous studies in the guinea-pig ureter, the present findings document the existence of remarkable regional differences in the effector mechanisms initiated by CGRP receptor occupancy in the guinea-pig pyeloureteral tract. CGRP appears to be inherently unable to activate glibenclamide-sensitive K channels in the guinea-pig renal pelvis, a mechanism which is central for its ability to suppress latent pacemakers in the ureter. Within the renal pelvis, the sensitivity to the inhibitory effect of CGRP appears in the more distal region, from which an 'ureter-like' action potential is recorded.