Effect of cromakalim and glibenclamide on spontaneous and evoked motility of the guinea-pig isolated renal pelvis and ureter

Propagation of Pacemaker Activity and Peristaltic Contractions in the Mouse Renal Pelvis Rely on Ca2+-activated Cl- Channels and T-Type Ca2+ Channels

The process of urine removal from the kidney occurs via the renal pelvis (RP). The RP demarcates the beginning of the upper urinary tract and is endowed with smooth muscle cells. Along the RP, organized contraction of smooth muscle cells generates the force required to move urine boluses toward the ureters and bladder. This process is mediated by specialized pacemaker cells that are highly expressed in the proximal RP that generate spontaneous rhythmic electrical activity to drive smooth muscle depolarization. The mechanisms by which peristaltic contractions propagate from the proximal to distal RP are not fully understood. In this study, we utilized a transgenic mouse that expresses the genetically encoded Ca²⁺ indicator, GCaMP3, under a myosin heavy chain promotor to visualize spreading peristaltic contractions in high spatial detail. Using this approach, we discovered variable effects of L-type Ca²⁺ channel antagonists on contraction parameters. Inhibition of T-type Ca²⁺ channels reduced the frequency and propagation distance of contractions. Similarly, antagonizing Ca²⁺-activated Cl^- channels or altering the transmembrane Cl^- gradient decreased contractile frequency and significantly inhibited peristaltic propagation. These data suggest that voltage-gated Ca²⁺ channels are important determinants of contraction initiation and maintain the fidelity of peristalsis as the spreading contraction moves further toward the ureter. Recruitment of Ca²⁺-activated Cl^- channels, likely Anoctamin-1, and T-type Ca²⁺ channels are required for efficiently conducting the depolarizing current throughout the length of the RP. These mechanisms are necessary for the efficient removal of urine from the kidney.

Ureteral motility

The pyeloureteral function is to transport urine from the kidneys into the ureter toward the urinary bladder for storage until micturition. A set of mechanisms collaborates to achieve this purpose: the basic process regulating ureteral peristalsis is myogenic, initiated by active pacemaker cells located in the renal pelvis. Great emphasis has been given to hydrodynamic factors, such as urine flow rate in determining the size and pattern of urine boluses which, in turn, affect the mechanical aspects of peristaltic rhythm, rate, amplitude, and baseline pressure. Neurogenic contribution is thought to be limited to play a modulatory role in ureteral peristalsis. The myogenic theory of ureteral peristalsis can be traced back to Engelmann (1) who was able to localize the peristaltic pressure wave's origin in the renal pelvis and suggested that the ureteral contraction impulse passes from one ureteral cell to another, the whole ureter working as a functional syncitium. Recent studies of ureteral biomechanics, smooth muscle cell electrophysiology, membrane ionic currents, cytoskeletal components and pharmacophysiology much improved our understanding of the mechanism of how the urine bolus is propelled, how this process is disturbed in pathological states, and what could be done to improve it.

Inhibition of human and pig ureter motility in vitro and in vivo by the K(+) channel openers PKF 217-744b and nicorandil

The relaxing property of the K(+) channel opener and nitric oxide donor nicorandil and the new K(+) channel opener PKF 217-744b was investigated on isolated human ureteral tissue in vitro and in intact ureters of anesthetized pigs in vivo. In addition, nicorandil and its antagonists, glibenclamide and methylene blue, were tested on isolated pig ureter tissue in vitro. Nicorandil decreased the frequency of spontaneous contractions in isolated pig ureter rings. This effect was antagonized by glibenclamide and methylene blue suggesting that the nicorandil induced relaxation of the ureter is mediated by activation of ATP-sensitive K(+) channels and involvement of soluble guanylate cyclase. Moreover, nicorandil and PKF 217-744b reduced the amplitude of electrically induced contractions in isolated human ureter rings. Calculations of EC(50) values showed that PKF 217-744b [EC(50) = 4.83 x 10(-8) M] was more potent than nicorandil [EC(50) = 4.38 x 10(-5) M]. Both drugs reduced the contraction frequency of the pig ureter after intravenous and topical administration in vivo. Intravenous, but not topical, administration of nicorandil and PKF 217-744b significantly decreased arterial blood pressure but did not affect the heart rate. The in vitro findings suggest that K(+) channel opening and nitric oxide release mediate the effect of nicorandil. Our in vivo results indicate that PKF 217-744b and nicorandil are promising drugs for clinical application in patients with acute stone colic to relieve obstruction and facilitate stone passage or to relax the ureter before ureteroscopy.

Systemic and topical drug administration in the pig ureter: effect of phosphodiesterase inhibitors alpha1, beta and beta2-adrenergic receptor agonists and antagonists on the frequency and amplitude of ureteral contractions

PURPOSE

We searched for compounds that are pharmacologically active on ureteral motility for treating ureteral colic to ease retrograde access into the ureter and improve the clearance of stones or stone particles from the ureter. The effects of the alpha1-adrenergic receptor agonist phenylephrine, the nonselective beta and beta2-adrenergic receptor agonists isoproterenol and fenoterol, and the phosphodiesterase inhibitors papaverine (nonspecific) and rolipram (type IV) on the frequency and amplitude of ureteral contractions when administered intravenously or topically were investigated in pigs.

MATERIALS AND METHODS

A total of 52 pigs were anesthetized. A double lumen 6Fr catheter was inserted through each renal pelvis and into the ureter, allowing perfusion of saline or drug solution into the renal pelvis and the recording of contractions from the mid portion of the ureter.

RESULTS

The alpha1 and beta-adrenergic receptors of the ureter are not tonically activated by endogenous epinephrine or norepinephrine. Phenylephrine administered intravenously at a dose of 0.01 to 3 mg./kg. and topically at 0.1 to 3 mg./ml. per minute increased contraction frequency 10 and 4-fold, respectively, and contraction amplitude 2-fold each in a dose dependent manner. Arterial blood pressure increased markedly during intravenous administration of phenylephrine but was minimally affected during topical application. The phenylephrine effects were reversed by the antagonist prazosin. Isoproterenol administered intravenously at a dose of 0.01 to 10 mg./kg. and topically at 0.1 to 200 microg./ml. per minute decreased contraction frequency to 13% and 31% of controls, respectively. Contraction amplitude was not affected by intravenous administration but decreased to 59% of controls when applied topically. These effects were also observed with a slight delay in the saline perfused contralateral ureter. The heart rate also increased, suggesting absorption of the drug by the urothelium. The isoproterenol effects were blocked by the antagonist propranolol. Fenoterol administered intravenously at a dose of 0.1 to 30 microg./kg. and topically at 0.003 to 1 mg./ml. per minute decreased contraction frequency to 14% and 10% of controls, and contraction amplitude to 84% and 65%, respectively. These effects on the drug perfused ureter were also observed on the contralateral saline perfused ureter but to a lesser extent. The fenoterol effects were blocked by the antagonist propranolol. Papaverine administered intravenously at a dose of 0.001 to 3 mg./kg. decreased contraction frequency to 33% of controls. Topically administered papaverine as well as intravenous and topically administered rolipram had no relevant effect on ureteral motility.

CONCLUSIONS

Intravenous phenylephrine increases, and isoproterenol and fenoterol decrease the frequency and amplitude of ureteral contractions in the pig. The same effects are observed with the topical administration of phenylephrine, which causes a significant local but not systemic side effect. Topical administration of isoproterenol and fenoterol produced local as well as systemic effects, suggesting absorption by the urothelium. However, to our knowledge a drug that relaxes ureteral peristalsis in pigs without causing systemic side effects has not yet been identified.

A2B adenosine receptors mediate relaxation of the pig intravesical ureter: adenosine modulation of non adrenergic non cholinergic excitatory neurotransmission

1. The present study was designed to characterize the adenosine receptors involved in the relaxation of the pig intravesical ureter, and to investigate the action of adenosine on the non adrenergic non cholinergic (NANC) excitatory ureteral neurotransmission. 2. In U46619 (10(-7) M)-contracted strips treated with the adenosine uptake inhibitor, nitrobenzylthioinosine (NBTI, 10(-6) M), adenosine and related analogues induced relaxations with the following potency order: 5'-N-ethylcarboxamidoadenosine (NECA) = 5'-(N-cyclopropyl)-carboxamidoadenosine (CPCA) = 2-chloroadenosine (2-CA) > adenosine > cyclopentyladenosine (CPA) = N6-(3-iodobenzyl)-adenosine-5'-N-methylcarboxamide (IB-MECA) = 2-[p-(carboxyethyl)-phenylethylamino]-5'-N-ethylcarboxamidoaden os ine (CGS21680). 3. Epithelium removal or incubation with indomethacin (3 x 10(-6) M) and L-N(G)-nitroarginine (L-NOARG, 3 x 10(-5) M), inhibitors of prostanoids and nitric oxide (NO) synthase, respectively, failed to modify the relaxations to adenosine. 4. 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 10(-8) M) and 4-(2-[7-amino-2-(2-furyl) [1,2,4]-triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM 241385, 3 x 10(-8) M and 10(-7) M), A1 and A2A receptor selective antagonists, respectively, did not modify the relaxations to adenosine or NECA. 8-phenyltheophylline (8-PT, 10(-5) M) and DPCPX (10(-6) M), which block A1/A2-receptors, reduced such relaxations. 5. In strips treated with guanethidine (10(-5) M), atropine (10(-7) M), L-NOARG (3 x 10(-5) M) and indomethacin (3 x 10(-6) M), both electrical field stimulation (EFS, 5 Hz) and exogenous ATP (10(-4) M) induced contractions of preparations. 8-PT (10(-5) M) increased both contractions. DPCPX (10(-8) M), NECA (10(-4) M), CPCA, (10(-4) M) and 2-CA (10(-4) M) did not alter the contractions to EFS. 6. The present results suggest that adenosine relaxes the pig intravesical ureter, independently of prostanoids or NO, through activation of A2B-receptors located in the smooth muscle. This relaxation may modulate the ureteral NANC excitatory neurotransmission through a postsynaptic mechanism.

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.

Involvement of a glibenclamide-sensitive mechanism in the nitrergic neurotransmission of the pig intravesical ureter

1. The present study was designed to investigate whether potassium (K+) channels are involved in the relaxations to nitric oxide (NO) of pig intravesical ureteral preparations suspended in organ baths for isometric tension recordings. In ureteral strips treated with guanethidine (10(-5) M) and atropine (10(-7) M) to block adrenergic neurotransmission and muscarinic receptors, respectively, NO was either released from nitrergic nerves by electrical field stimulation (EFS, 0.5-10 Hz., 1 ms duration, 20 s trains), or exogenously-applied as an acidified solution of sodium nitrite (NaNO2, 10(-6)-10(-3) M). 2. Incubation with an inhibitor of guanylate cyclase activation by NO, methylene blue (10(-5) M) did not change the basal tension of intravesical ureteral strips but inhibited the relaxation induced by EFS or exogenous NO on ureteral preparations contracted with the thromboxane analogue U46619 (10(-7) M). 3. Incubation with charybdotoxin (3 x 10(-8) M) and apamin (5 x 10(-7) M), which are inhibitors of large and small conductance calcium (Ca2+)-activated K+ channels, respectively, did not modify basal tension or the relaxations induced by EFS and exogenous NO. Treatment with charybdotoxin or apamin plus methylene blue (10(-5) M) significantly reduced the relaxations to EFS and exogenous NO. However, in both cases the reductions were similar to the inhibition evoked by methylene blue alone. The combined addition of charybdotoxin plus apamin did not change the relaxations to EFS or exogenously added NO of the porcine intravesical ureter. 4. Cromakalim (10(-8) 3 x 10(-6) M), an opener of ATP-sensitive K+ channels, evoked a dose-dependent relaxation with a pD2 of 7.3 +/- 0.2 and maximum relaxant effect of a 71.8 +/- 4.2% of the contraction induced by U46619 in the pig intravesical ureter. The blocker of ATP-sensitive K+ channels, glibenclamide (10(-6) M), inhibited markedly the relaxations to cromakalim. 5. Glibenclamide (10(-6) M) had no effect on the basal tone of ureteral preparations but significantly reduced the relaxations induced by both EFS and exogenous NO. Combined treatment with methylene blue (10(-5) M) and glibenclamide (10(-6) M) did not exert an effect greater than that of methylene blue alone on either EFS- or NO-evoked relaxations of the pig ureter. 6. The present results suggest that NO acts as an inhibitory neurotransmitter in the pig intravesical ureter and relaxes smooth muscle through a guanylate cyclase-dependent mechanism which seems to favour the opening of glibenclamide-sensitive K+ channels.

Role of intracellular Ca2+ in the K channel opener action of CGRP in the guinea-pig ureter

1. The aim of this study was to assess the role of sarcoplasmic reticulum (SR) calcium (Ca2+) in the smooth muscle relaxant and hyperpolarizing actions of calcitonin gene-related peptide (CGRP) in the guinea-pig ureter. 2. CGRP (0.1 microM) rapidly and transiently reduced myogenic phasic contractions (twitches) produced by electrical field stimulation (EFS). Approximately 70% of the response to CGRP was antagonized by glibenclamide (1 microM). 3. Cyclopiazonic acid (CPA, 10 microM), ryanodine (100 microM) and thapsigargin (1 microM) reduced only the glibenclamide-sensitive component of the response to CGRP (0.1 microM) but did not modify the mechano-inhibitory effect of cromakalim (3 microM). A low concentration of CPA (1 microM), assumed to produce a limited impairment of Ca2+ uptake from the stores, prolonged the duration of the inhibitory response to CGRP. Pre-exposure to caffeine (5 mM) inhibited the suppression of twitches by CGRP or cromakalim. 4. When the frequency of EFS was increased, the suppression of twitches by CGRP was reduced. Under these conditions, CPA (1 microM) again prolonged the duration of the inhibitory response to CGRP. 5. CGRP (0.1 microM) and cromakalim (3 microM) markedly depressed the phasic component of contractions to 80 mM KCl. CPA (10 microM) antagonized the inhibitory effect of CGRP but not that of cromakalim. Inhibition of the tonic contraction to 80 mM KCl by CGRP was insensitive to CPA. 6. In sucrose gap experiments, a 5 min exposure to CGRP (0.1 microM) or cromakalim (3 microM) produced a sustained membrane hyperpolarization. Caffeine (5 mM) produced a glibenclamide-sensitive transient hyperpolarization followed by a sustained depolarization. When tested in a Ca(2+)-free medium the hyperpolarization produced by CGRP, cromakalim or caffeine was reduced. In normal Krebs, pre-exposure to CPA (10 microM, 60 min) only abolished the hyperpolarization induced by CGRP. In contrast, 5 min after a caffeine challenge (5 mM) the hyperpolarizations induced by CGRP or cromakalim were reduced. The CGRP-induced hyperpolarization was insensitive to apamin (0.1 microM) or charybdotoxin (0.1 microM). 7. We conclude that the K channel-opening action of CGRP in the guinea-pig ureter requires the mobilization of intracellular Ca2+ from a caffeine- and CPA-sensitive store, leading to transient activation of glibenclamide-sensitive K channels. The K channel-opening action of caffeine appears to involve Ca2+ mobilization from a store which is insensitive to depletion by CPA.

Effects of potassium channel modulators cromakalim, tetraethylammonium and glibenclamide on the contractility of the isolated human ureter

PURPOSE

Experiments were performed to assess the effect of the potassium channel modulators cromakalim, tetraethylammonium (TEA) and glibenclamide on the contractility of isolated human ureteric rings.

MATERIALS AND METHODS

Segments of human distal ureter obtained from kidney donors (leftovers) were cut into rings and suspended in an organ bath filled with modified Tyrode solution for measurement of isometric contractile force. The ureter was stimulated electrically or with KCl, and the contractile activity recorded on a polygraph.

RESULTS

The amplitude of the contraction induced by electrical stimulation was not changed by glibenclamide but was enhanced by tetraethylammonium. The resting tension of the ureter was not changed by either potassium channel inhibitor. Cromakalim did not change the resting tension of the human ureter per se but induced a concentration-dependent inhibition of the contractions induced by electrical stimulation. This inhibitory effect of cromakalim was not changed by tetraethylammonium but was inhibited by glibenclamide. A phasic and tonic contractile response in the isolated human ureteric ring was induced by 60 mM. KCl. The phasic contractions were abolished by cromakalim whereas the tonic contractions were unaffected. Following sustained contraction induced by 25 mM. KCl, the cumulative addition of cromakalim to the organ bath produced a concentration-dependent relaxation. However, in rings precontracted with 60 mM. KCl, cromakalim at a concentration as high as 10(-5) M. did not induce relaxation. The cromakalim-induced relaxation of rings precontracted with 25 mM. KCl was significantly inhibited by glibenclamide.

CONCLUSION

These results suggest that potassium channels are important in the control of human ureter contractility and that potassium channel openers may be an alternative therapeutic indication in the treatment of human ureteric colic.

Effect of exercise and 2-deoxyglucose on the K+ channel opener action of CGRP in the guinea pig ureter

1. In the guinea pig isolated ureter, a maximally effective concentration of calcitonin gene-related peptide (CGRP, 0.1 microM) produced a prompt and transient suppression of myogenic phasic contractions (twitches) evoked by direct excitation (electrical field stimulation, EFS) of the smooth muscle. This suppressant effect is prevented by glibenclamide (1 and 10 microM), indicating the importance of K+ channel activation in its genesis. In the presence of either 1 or 10 microM glibenclamide, CGRP produced a partial (about 30%) and delayed inhibition of the evoked response, but failed to produce a full suppression of twitches. 2. The intensity and duration of the early, glibenclamide-sensitive suppressant effect of CGRP were inversely related to the frequency at which the ureters were driven by EFS. The glibenclamide-resistant inhibitory effect of CGRP was unaffected by changes in the EFS driving frequency, and cromakalim (3 microM) suppressed twitches independently of the EFS driving frequency. 3. Replacement of 80% glucose in the Krebs solution with 2-deoxyglucose (2-DOG) reduced the amplitude of the EFS-evoked twitches. In the presence of 2-DOG the inhibitory effect of CGRP was enhanced and prolonged when tested in the absence, but not in the presence, of glibenclamide. 2-DOG counteracted the inhibitory effect produced by increasing the EFS driving frequency on the response to CGRP. 4. In sucrose gap, both CGRP (0.1 microM) and cromakalim (3 microM) produced prompt hyperpolarization of the membrane. During continued superfusion for 15 min in unstimulated preparations, the hyperpolarizing effect of cromakalim and CGRP was sustained. When tested within 3 min from the end of 'exercise', induced by application of EFS at intervals of 15 sec for 30 min, the hyperpolarization by CGRP was reduced and shortened but that produced by cromakalim was unaffected. 5. These findings demonstrate that exercise and metabolic inhibition selectively influence, in opposite directions, the K+ channel opener action of CGRP in the guinea pig ureter, indicating that the ability of this neuropeptide to suppress latent pacemakers in smooth muscle is markedly dependent upon degree/frequency of cell activation. These results suggest that the ability of endogenous CGRP to suppress ureteral motility may be inversely related to the frequency of ureteral peristalsis, the effect being reduced by, for example, increase in diuresis.

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.

Role of cyclic AMP and protein kinase A in K+ channel activation by calcitonin gene-related peptide (CGRP) in the guinea-pig ureter

1. The aim of this study was to assess whether agents that interfere with the intracellular actions of cAMP and activation of protein kinase A (PKA) prevent the inhibitory action of human alpha-calcitonin gene-related peptide (CGRP) in the guinea-pig ureter smooth muscle. The action of CGRP was compared to that of the K+ channel opener, cromakalim, and the adenylyl cyclase activator, forskolin, toward electrical field stimulation- (EFS) induced myogenic twitch contractions of the ureter. To further verify the role of cAMP in the action of CGRP, we also studied the effect of stable cAMP analogues and of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX). 2. Maximally effective concentrations of CGRP (0.1 microM) or forskolin (10 microM) produced a transient suppression of twitches. Cromakalim (3 microM) likewise produced a prompt suppression of twitches that in most cases exceeded 15 min. The early suppressant effect of CGRP or forskolin was inhibited by 1 or 10 microM glibenclamide; about 30% of the effect of CGRP was glibenclamide-resistant. The effect of cromakalim was totally suppressed by glibenclamide. 3. The inhibitory effect of CGRP was concentration-dependently reduced by low concentrations of barium chloride (IC50 63 microM), which blocked with similar potency the inhibitory action of cromakalim (IC50 60 microM). Glibenclamide (10 nM-10 microM) concentration-dependently inhibited the effect of CGRP and cromakalim with IC50S of 0.13 and 0.72 microM, respectively. 4. The cAMP analogues dibutyrye-cAMP (1-3 mM), 8-(4-chlorophenylthio)cAMP (0.3-1 mM) and Sp-cAMP monophosphothioate (0.1-0.3 mM) were either ineffective or poorly effective in inhibiting twitches. The cGMP analog, 8Br-cGMP (100-300 microM) produced a slowly developing, glibenclamide (1 microM)-resistant partial inhibition (25-30%) of twitches. 5. IBMX (1-300 microM) produced a concentration-dependent inhibition of twitches (EC50 16 microM). IBMX (100 microM) produced a large (peak 91%) and transient inhibition: glibenclamide (1 microM) blocked the early peak of the inhibitory action of IBMX, similar to the effect observed toward CGRP and forskolin.

Calcitonin gene related peptide as inhibitory neurotransmitter in the ureter

A dense plexus of calcitonin gene related peptide (CGRP) containing nerve fibres is present in the mammalian ureter, from which CGRP is released by depolarizing stimuli, including chemical normally present in the urine. CGRP exerts a profound, receptor-mediated, inhibitory effect on the evoked motility of the ureter by suppressing latent pacemakers in the smooth muscle. This effect is largely glibenclamide sensitive, indicating the activation of potassium (K) channels in its genesis. Electrical stimulation of intramural nerves in the guinea-pig ureter produces a transient membrane hyperpolarization, which is blocked by glibenclamide or by capsaicin pretreatment, enhanced in a low-K medium, and inhibited by a CGRP receptor antagonist. Thus endogenous CGRP acts as a neurotransmitter K channel opener in the ureter. The refractory period of the guinea-pig ureter is markedly and similarly reduced by capsaicin pretreatment or administration of a CGRP receptor antagonist, indicating that endogenous CGRP can modulate the maximal frequency of ureteral peristalsis. Using a three-chamber organ bath that enabled the separate perfusion of the renal, middle, and bladder regions of the organ, evidence was obtained that CGRP blocks propagation of impulses along the ureter through a glibenclamide-sensitive mechanism. These findings indicate a role of CGRP in the local regulation of ureteral motility and peristalsis.

Calcitonin gene-related peptide selectively increases cAMP levels in the guinea-pig ureter

Calcitonin gene-related peptide (CGRP, 0.1 microM) and forskolin (10 microM) both produced a time-dependent accumulation of cAMP in homogenates of the guinea-pig ureter, while cromakalim (3 microM) was ineffective. Neither agent did increase the cGMP levels. cAMP accumulation induced by CGRP or forskolin was unchanged by glibenclamide (1 microM). In sucrose gap, the application of forskolin (1-10 microM for 15 s) hyperpolarized the smooth muscle membrane and its effect was greatly enhanced when tested in a low-K+ medium (extracellular K+ reduced from 5.9 to 1.2 mM). The hyperpolarization produced by 10 microM forskolin was reduced and abolished by 1 and 10 microM glibenclamide, respectively, in both normal and low-K+ medium. The present findings demonstrate that CGRP determines a selective cAMP accumulation in the guinea-pig ureter and suggest that elevation of cAMP may be involved in the opening of glibenclamide-sensitive K+ channels in the ureter smooth muscle.

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

1. The effects of the (S)- and (R)-enantiomers of the cyclo-oxygenase (COX) inhibitor, ketoprofen, have been investigated on the spontaneous activity of the guinea-pig isolated renal pelvis and on electrical field stimulation-(EFS) induced contractions of the guinea-pig ureter in comparison with the effects of the achiral COX inhibitor, indomethacin. 2. (S)-ketoprofen (0.1-100 microM) produced a concentration- and time-dependent inhibition of the spontaneous myogenic activity of the renal pelvis. The maximal inhibitory effect (% inhibition of motility index) averaged 29, 42, 47 and 56% inhibition of control values at 0.1, 1, 10 and 100 microM. The (R)-enantiomer was ineffective up to 10 microM. 3. Indomethacin (0.1-100 microM) likewise produced a concentration- and time-dependent inhibition of spontaneous motility of the isolated renal pelvis: its maximal inhibitory effect was larger than that produced by (S)-ketoprofen and averaged 21, 40, 69 and 95% inhibition of motility index at 0.1, 1, 10 and 100 microM respectively. In the presence of a maximally effective (100 microM) concentration of (S)-ketoprofen, 100 microM indomethacin produced > 90% inhibition of residual motility. 4. In the guinea-pig isolated ureter, phasic contractions were induced by EFS (5 ms pulse width, 60 V): (S)-ketoprofen (100-500 microM) had no effect on the EFS-evoked contractions. Indomethacin (100-500 microM) produced a concentration-dependent inhibition and/or suppression of the EFS-evoked contractions. When contraction of the ureter was evoked by 80 mM KCl, indomethacin produced about 30 and 80% inhibition at 100 and 300 microM, respectively, while (S)-ketoprofen (300 microM) was ineffective. 5. The effect of (S)-ketoprofen or indomethacin (10 microM each) on the propagation of myogenic impulses along the ureter was determined by use of a three chamber organ bath. The renal end of the ureter was electrically stimulated while recording the mechanical activity of the renal and bladder ends of the ureter: addition of either (S)-ketoprofen or indomethacin (10 microM) did not effect propagation of impulses from the renal to the bladder end of the ureter, while nifedipine (10 microM) promptly blocked the propagated contractions. 6. In sucrose gap experiments, (S)-ketoprofen (10-100 microM) produced a time-dependent shortening of spontaneous action potentials of the guinea-pig renal pelvis and reduced the amplitude and duration of the accompanying phasic contractions. Indomethacin (10 microM) produced comparable effects on the same parameters and significantly reduced the maximal amplitude of depolarization of the pacemaker potential. In the presence of 100 microM (S)-ketoprofen, 100 microM indomethacin promptly suppressed the residual pacemaker potential and contraction.7. Neither (S)-ketoprofen nor indomethacin (10 microM each for 60 min) affected the parameters of action potential and contraction of the guinea-pig ureter evoked by EFS. Both drugs produced a sustained membrane depolarization.8. The present findings demonstrate that stereoselective COX inhibition affects pacemaker potentials and contractility (electromechanical coupling) in the guinea-pig renal pelvis. The modulatory role of endogenous prostanoids involves an amplification of electromechanical coupling in the renal pelvis while excitability, contractility or propagation of impulses along the ureter appear almost independent of prostanoid generation. Previous reports of a total suppression of pyeloureteral motility by indomethacin may reflect a combination of COX inhibition and nonspecific effect on electromechanical coupling.

Effect of the Ca(2+)-ATPase inhibitor, cyclopiazonic acid, on electromechanical coupling in the guinea-pig ureter

1. We have investigated the effect of the sarcoplasmic reticulum (SR) Ca(2+)-ATPase inhibitor, cyclopiazonic acid (CPA), on electromechanical coupling in the guinea-pig ureter. All experiments were performed in capsaicin-pretreated (10 microM for 15 min) ureters to prevent the release of sensory neuropeptides from afferent nerves. 2. In organ bath experiments, electrical field stimulation (EFS, 10 Hz for 1 s, 5 ms pulse width, 60 V) produced tetrodotoxin- (1 microM) resistant phasic contractions which were enhanced by Bay K 8644 (1 microM) and abolished by nifedipine (10-30 microM). 3. CPA (10 microM) enhanced the EFS-evoked contractions both in the absence and presence of Bay K 8644. The effect of CPA was concentration-dependent between 1 and 30 microM. The response to 10 microM CPA was biphasic: the maximal enhancement (58 +/- 3% increase) was observed within 10-20 min from CPA administration, followed by a decline to a new steady state (25 +/- 5% increase over baseline) at 50-60 min. The effect of CPA was reversed by washout. 4. Ryanodine (100 microM) produced a prompt enhancement of the EFS-evoked contractions of the guinea-pig ureter, which peaked at 42 +/- 3% increase over baseline; the co-administration of CPA (10 microM) and ryanodine (100 microM) produced a peak effect (60 +/- 8% enhancement) which was not different from that produced by CPA alone. With either ryanodine alone or ryanodine plus CPA, the enhancement of the EFS-induced contractions was biphasic, showing a time-course similar to that observed with CPA alone. Tetraethylammonium (10 mM) produced a significantly larger effect (93 +/- 13% increase over baseline) and its effect was sustained throughout the 60 min observation period. 5. In the presence of Bay K 8644, superfusion for 30 min with a low Na+ medium (60% of extracellular Na+ replaced by Li+ or choline) reduced the amplitude of EFS-evoked contractions by 20-35%. In both Li(+)- and choline-substituted media, spontaneous activity developed during superfusion with low Na+ Krebs solution which was suppressed by 10 microM nifedipine. CPA (10 microM) produced a marked enhancement of the EFS-evoked contractions in low-Na+ medium (both Li(+)- and choline-substituted) and this effect was sustained throughout the 60 min observation period. 6. In the absence of Bay K 8644, the response of the ureter smooth muscle to EFS is characterized by a refractory period: an interval of about 30 s was required between two applied stimuli to produce a second response comparable in size to that elicited by the first stimulus. CPA (10 micro M, 10-20 min before)markedly reduced the refractory period of the guinea-pig ureter to EFS.7. CPA (10 micro M, 30-60 min before) increased the phasic component of contraction produced by 80 m MKCl. The tonic component of the response to KCl was slightly but not significantly reduced by CPA,and a 'hump' in the tonic contraction was observed at 1-2 min from addition of KCl.8. In sucrose gap experiments, 10 micro M CPA produced a sustained depolarization of the membrane and reduced the latency between application of electrical stimuli and onset of the action potential; these effects were maintained throughout the 60 min superfusion with CPA. CPA also transiently prolonged the plateau phase of the action potential and increased the peak amplitude of contraction: these effects peaked at about 10-20 min from start of superfusion with CPA and then declined. At the peak of its enhancing effect on contraction amplitude, CPA prolonged the contractile phase of the contraction relaxation cycle.9.Superfusion with a low-Na, choline-substituted Krebs solution produced a reversible membrane depolarization. In the presence of Bay K 8644 (1 micro M), action potentials and phasic contractions were superimposed on this depolarization which were abolished by nifedipine (1O micro M).10. These findings indicate that CPA augments the excitability and affects the contraction-relaxation cycle of the smooth muscle of the guinea-pig ureter, implying a role for sarcoplasmic reticulum Ca2+-ATPase in the regulation of electromechanical coupling. The effects of CPA resemble those produced by ryanodine and the effect of the two agents on the amplitude of contractions is non-additive.It appears that following blockade of the CPA-sensitive SR Ca2+ pump, other mechanism(s) may come into action to reduce intracellular Ca2+. The Na+/Ca2+ exchanger could be involved in the compensatory changes responsible for the fading of the response to CPA.

Propagation of impulses in the guinea-pig ureter and its blockade by calcitonin gene-related peptide (CGRP)

The guinea-pig ureter was placed in a three-compartment organ bath to enable the application of electrical stimuli or drugs to its renal end (R-site), the middle region (M-site) or the bladder end (B-site) while recording mechanical activity at the R- and B-sites. All experiments were performed in ureters pre-exposed to capsaicin (10 microM for 15 min) to prevent the release of sensory neuropeptides from afferent nerves. Electrical field stimulation (EFS, 5-25 ms pulse width, 20 V) produced a phasic contraction at the site of stimulation ('direct' response to EFS) which propagated to the other end of the ureter. Section of the ureter at the M-site abolished the propagated response to EFS; after section, EFS applied at the M-site induced a phasic contraction at both the R- and B-sites. Likewise, the application of KCl at the M-site produced phasic contractions at both the R- and B-sites. Tetrodotoxin (1 microM), nifedipine (1 microM) or Bay K 8644 (1 microM) applied at the M-site had no influence on the direct or propagated responses to EFS; nifedipine (10 microM) applied at the M-site abolished the propagated responses without affecting the direct responses to EFS. Bay K 8644 (1 microM) applied at the R-site produced a marked enhancement of the direct response (EFS applied at R-site) while having no effect on the amplitude of the propagated response to EFS.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple mechanisms in the smooth muscle relaxant action of calcitonin gene-related peptide (CGRP) in the guinea-pig ureter

We have investigated the ability of human alpha CGRP (CGRP) to inhibit the electrically-evoked myogenic contractions of the guinea-pig ureter, in comparison with the K channel opener, cromakalim, and the adenylate cyclase activator, forskolin. CGRP (0.1 nM-0.1 microM) produced a concentration-dependent inhibition of the evoked contractions; its action was prevented by the CGRP receptor antagonist, CGRP(8-37) (1 microM), while it was unaffected by the nitric oxide (NO) synthase inhibitor, L-nitroarginine (30 microM). The effect of CGRP was antagonized in a noncompetitive manner (depression of Emax, no change in EC50) by glibenclamide (1-10 microM), a blocker of ATP-sensitive potassium channels (KATP). A substantial fraction of the inhibitory effect of CGRP was glibenclamide-resistant, however. Glibenclamide also blocked the inhibitory action of cromakalim (0.1-10 microM) without affecting the inhibition produced by forskolin (0.1-30 microM). When tested in a low-K medium (extracellular K reduced from 5.9 to 1.2 mM), the inhibitory effects of CGRP, cromakalim and forskolin were enhanced. The inhibitory effect of forskolin was partly antagonized by glibenclamide when tested in a low-K medium. CGRP (0.1 microM), cromakalim (3 microM) and forskolin (10 microM) inhibited the contractile response to KCl (80 mM), which is characterized by a distinct phasic and tonic component: cromakalim selectively inhibited the phasic response to KCl with CGRP and forskolin inhibited both components. The inhibitory effect of CGRP on the phasic contraction to KCl was partly glibenclamide-(1 microM) sensitive, while that on the tonic contraction was glibenclamide-resistant. The inhibitory action of forskolin on both components of the response to KCl was unchanged by glibenclamide.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory transmitter action of calcitonin gene-related peptide in guinea-pig ureter via activation of glibenclamide-sensitive K channels

1. In single sucrose gap, electrical field stimulation (EFS, 1-5 Hz) produced graded hyperpolarization of the membrane of the guinea-pig ureter smooth muscle, which was blocked by tetrodotoxin (0.3 microM) or in vitro capsaicin desensitization (3 microM for 15 min). Capsaicin itself produced a transient hyperpolarization of the membrane on its first application. 2. Superfusion with human alpha calcitonin gene-related peptide (CGRP, 30-300 mM) likewise produced a transient hyperpolarization of the membrane, mimicking the neurogenic inhibitory junction potential (i.j.p.). The hyperpolarization by CGRP was unaffected by tetrodotoxin, indicating a postjunctional site of action. 3. Both the EFS-evoked i.j.p. and the CGRP-induced hyperpolarization were inhibited by the CGRP receptor antagonist, CGRP(8-37) (0.3-3 microM) which did not affect the hyperpolarization produced by the KATP channel opener, cromakalim (0.3 microM). 4. The KATP channel blocker, glibenclamide (1 microM) blocked both the EFS-evoked i.j.p. and the CGRP-induced hyperpolarization. 5. When evoked in a low K medium (1.2 mM, KCl being replaced by an equimolar amount of NaCl), the EFS-evoked i.j.p. and the CGRP-induced hyperpolarization were both markedly enhanced, consistent with the idea that opening of K channels underlies both responses. 6. The present findings provide direct electrophysiological evidence for a neurotransmitter role of CGRP, released from the peripheral endings of capsaicin-sensitive primary afferent neurones, in the guinea-pig ureter. The action of both exogenous and endogenous CGRP involves the activation of glibenclamide-sensitive (KATP) potassium channels.

A thiorphan-sensitive mechanism regulates the action of both exogenous and endogenous calcitonin gene-related peptide (CGRP) in the guinea-pig ureter

The aim of this study was to assess the existence of mechanisms regulating the intensity and duration of action of calcitonin gene-related peptide (CGRP), the main candidate inhibitory transmitter released from capsaicin-sensitive afferents in the guinea-pig ureter. In a first series of experiments, performed in capsaicin-pretreated ureters, exogenously administered human alpha CGRP (h alpha CGRP) produced inhibition of contractions of the guinea-pig isolated ureter evoked by direct electrical stimulation of smooth muscle. The intensity and duration of the inhibitory effect of h alpha CGRP were potentiated by the inhibitor of neutral endopeptidase, thiorphan, while captopril and bestatin were without effect. In a second series of experiments, background motility of the guinea-pig ureter was evoked by administration of endothelin-1 (ET-1): electrical stimulation of intramural nerves produced a transient suppression of the ET-1-evoked contractions, ascribable to release of endogenous CGRP. Thiorphan enhanced the inhibitory effect produced by endogenous CGRP, while bestatin and captopril were without effect. These findings demonstrate that a thiorphan-sensitive mechanism, presumably neutral endopeptidase, regulates the intensity and duration of the inhibitory activity of both exogenous and endogenous CGRP in the guinea-pig ureter. The existence of a mechanisms for inactivation of the released peptide is consistent with the proposed role of CGRP as inhibitory neurotransmitter in this preparation.