Dual capsaicin effects on ureteric motility: low dose inhibition mediated by calcitonin gene-related peptide and high dose stimulation by tachykinins?

TRPM3 channel activation inhibits contraction of the isolated human ureter via CGRP released from sensory nerves

AIMS

Sensory nerve activation modulates ureteral contractility by releasing neuropeptides including CGRP and neurokinin A (NKA). TRPM3 is a recently discovered thermosensitive channel expressed in nociceptive sensory neurons, and plays a key role in heat nociception and chronic pain. The aim of this study is to examine the role of TRPM3 activation in human ureter motility.

MAIN METHOD

Human proximal ureters were obtained from fourteen patients undergoing nephrectomy. Spontaneous or NKA-evoked contractions of longitudinal ureter strips were recorded in an organ bath. Ureteral TRPM3 expression was examined by immunofluorescence.

KEY FINDINGS

Spontaneous contractions were observed in 60% of examined strips. TRPM3 activation using pregnenolone sulphate (PS) or CIM0216 (specific TRPM3 agonists) dose-dependently reduced the frequency of spontaneous and NKA-evoked contractions, with IC50s of 241.7 μM and 4.4 μM, respectively. The inhibitory actions of TRPM3 agonists were mimicked by CGRP (10 to 100 nM) or a cAMP analogue (8-Br-cAMP; 1 mM). The inhibitory actions of TRPM3 agonists (300 μM PS or 30 μM CIM0216) were blocked by pretreatment with primidone (TRPM3 antagonist; 30 μM), tetrodotoxin (sodium channel blocker; 1 μM), olcegepant (CGRP receptor antagonist; 10 μM), or H89 (non-specific PKA inhibitor; 30 μM). TRPM3 was co-expressed with CGRP in nerves in the sub-urothelial and intermuscular regions of the ureter.

SIGNIFICANCE

TRPM3 channels expressed on sensory terminals of the human ureter involve in inhibitory sensory neurotransmission and modulate ureter motility via the CGRP-cAMP-PKA signal pathway. Targeting TRPM3 may be a pharmacological strategy for promoting the ureter stone passage.

Pacemaker Mechanisms Driving Pyeloureteric Peristalsis: Modulatory Role of Interstitial Cells

The peristaltic pressure waves in the renal pelvis that propel urine expressed by the kidney into the ureter towards the bladder have long been considered to be 'myogenic', being little affected by blockers of nerve conduction or autonomic neurotransmission, but sustained by the intrinsic release of prostaglandins and sensory neurotransmitters. In uni-papilla mammals, the funnel-shaped renal pelvis consists of a lumen-forming urothelium and a stromal layer enveloped by a plexus of 'typical' smooth muscle cells (TSMCs), in multi-papillae kidneys a number of minor and major calyces fuse into a large renal pelvis. Electron microscopic, electrophysiological and Ca²⁺ imaging studies have established that the pacemaker cells driving pyeloureteric peristalsis are likely to be morphologically distinct 'atypical' smooth muscle cells (ASMCs) that fire Ca²⁺ transients and spontaneous transient depolarizations (STDs) which trigger propagating nifedipine-sensitive action potentials and Ca²⁺ waves in the TSMC layer. In uni-calyceal kidneys, ASMCs predominately locate on the serosal surface of the proximal renal pelvis while in multi-papillae kidneys they locate within the sub-urothelial space. 'Fibroblast-like' interstitial cells (ICs) located in the sub-urothelial space or adventitia are a mixed population of cells, having regional and species-dependent expression of various Cl^-, K⁺, Ca²⁺ and cationic channels. ICs display asynchronous Ca²⁺ transients that periodically synchronize into bursts that accelerate ASMC Ca²⁺ transient firing. This review presents current knowledge of the architecture of the proximal renal pelvis, the role Ca²⁺ plays in renal pelvis peristalsis and the mechanisms by which ICs may sustain/accelerate ASMC pacemaking.

Characterization of capsaicin induced responses in mice vas deferens: evidence of CGRP uptake

Calcitonin gene-related peptide (CGRP) is extensively distributed in primary afferent sensory nerves, including those innervating the genitourinary tract. Capsaicin can stimulate the release of CGRP from intracellular stores of these nerves, but this phenomenon has not been investigated in-depth in isolated preparations. The present study sets out to study and characterize the capsaicin as well as CGRP-induced responses in isolated mouse vas deferens. The effects of capsaicin and CGRP family of peptides were studied on electrically-induced twitch responses in the absence or presence of transient receptor potential cation channel vanilloid subfamily member 1 (TRPV1) antagonist and CGRP receptor antagonists. Twitch responses were attenuated by capsaicin (1nM-30nM) and CGRP family of peptides. The potency order was CGRP>intermedin-long (IMDL)~[Cys(Et)(2,7)]αCGRP~adrenomedullin (AM)>[Cys(ACM)(2,7)]αCGRP>amylin (AMY). These responses were disinhibited by the CGRP receptor antagonists and TRPV1 antagonists. The addition of CGRP receptor antagonists caused a transient potentiation of the twitch response and this potentiation was blocked by pretreatment with capsaicin and enhanced by incubation with exogenous CGRP. During the second consecutive cumulative concentration-response curve with capsaicin, the first phase of concentration-response curve disappeared and this was partially restored when the mouse vas deferens was preincubated with CGRP, suggesting the uptake of exogenous CGRP by nerves. Besides showing capsaicin-induced CGRP releases this study shows that exogenous CGRP can be taken up in vas deferens and can be re-released. CGRP uptake will add another dimension in understanding the homeostasis of this neuropeptide.

Physiology and pharmacology of the human ureter: basis for current and future treatments

INTRODUCTION

This article sets out to be a review regarding agents that affect contraction and relaxation of the ureter in order to establish a basis for current and future treatments for upper urinary tract obstruction.

MATERIAL AND METHODS

A complete review of the English literature using MEDLINE was performed between 1960 and 2007 on ureter physiology and pharmacology with special emphasis on signal transduction mechanisms involved in the contractile regulation of the human ureter.

RESULTS

Activation of muscarinic and adrenergic receptors increases the amplitude of ureteral contractions. The sympathetic nerves modulate the contractions by alpha-adrenoceptors and relaxation by beta-adrenoceptors. The purinergic system is important in sensory/motor functions and ATP is an important non-adrenergic non-cholinergic (NANC) agent causing contraction. Nitric oxide (NO) is a major inhibitory NANC neurotransmitter causing relaxation. Serotonin causes contraction. Prostaglandin-F(2)alpha contracts whereas prostaglandin-E(1)/E(2) relaxes the ureter. Phosphodiesterases (PDE) and the Rho-kinase pathway have recently been identified in the human ureter. PDE-IV inhibitors, K(+) channel openers, calcium antagonists, alpha(1)-adrenoceptor antagonists and NO donors seem to be promising drugs in relieving obstruction and facilitating stone passage.

CONCLUSIONS

Further understanding of the ureteral function and pharmacology may lead to the discovery of promising new drugs that could be useful in relieving ureteral colic, facilitating spontaneous stone passage, preparing the ureter for ureteroscopy as well as acting adjunctive to extracorporeal shock-wave lithotripsy.

The vanilloid receptor and hypertension

Mammalian transient receptor potential (TRP) channels consist of six related protein sub-families that are involved in a variety of pathophysiological function, and disease development. The TRPV1 channel, a member of the TRPV sub-family, is identified by expression cloning using the "hot" pepper-derived vanilloid compound capsaicin as a ligand. Therefore, TRPV1 is also referred as the vanilloid receptor (VR1) or the capsaicin receptor. VR1 is mainly expressed in a subpopulation of primary afferent neurons that project to cardiovascular and renal tissues. These capsaicin-sensitive primary afferent neurons are not only involved in the perception of somatic and visceral pain, but also have a "sensory-effector" function. Regarding the latter, these neurons release stored neuropeptides through a calcium-dependent mechanism via the binding of capsaicin to VR1. The most studied sensory neuropeptides are calcitonin gene-related peptide (CGRP) and substance P (SP), which are potent vasodilators and natriuretic/diuretic factors. Recent evidence using the model of neonatal degeneration of capsaicin-sensitive sensory nerves revealed novel mechanisms that underlie increased salt sensitivity and several experimental models of hypertension. These mechanisms include insufficient suppression of plasma renin activity and plasma aldosterone levels subsequent to salt loading, enhancement of sympathoexcitatory response in the face of a salt challenge, activation of the endothelin-1 receptor, and impaired natriuretic response to salt loading in capsaicin-pretreated rats. These data indicate that sensory nerves counterbalance the prohypertensive effects of several neurohormonal systems to maintain normal blood pressure when challenged with salt loading. The therapeutic utilities of vanilloid compounds, endogenous agonists, and sensory neuropeptides are also discussed.

Calcitonin gene-related peptide (CGRP) expression in the human neonatal paravertebral ganglia

The distribution of calcitonin gene-related peptide-immunoreactivity (CGRP-IR) in human neonatal paravertebral ganglia was demonstrated by the method of indirect immunohistochemistry. A marked population (up to 21%) of CGRP-IR neurons and varicose nerve fibres was observed. The number of calcionin gene-related peptide-immunoreactive neurons varied from ganglion to ganglion in the sympathetic trunk. In addition to its cotransmitter functions, the existence of CGRP in neonatal ganglionic nerve cells was suggested by its inductive and trophic actions on the growth and differentiation of neurons.

Excitatory motor and electrical effects produced by tachykinins in the human and guinea-pig isolated ureter and guinea-pig renal pelvis

1. In isolated tissue experiments, neurokinin A (NKA) produced concentration-dependent contraction of human and guinea-pig ureter (pD2 = 6.7 and 7.2, respectively); an effect greatly reduced (>80% inhibition) by the tachykinin NK2 receptor-selective antagonist MEN 11420 (0.1 microM). The tachykinin NK1 and NK3 receptor agonists septide and senktide, respectively, were ineffective. 2. Electrical field stimulation (EFS) of the guinea-pig isolated renal pelvis produced an inotropic response blocked by MEN 11420 (0.01-1 microM). In the same preparation MEN 11420 (0.1 microM) blocked (apparent pK(B) = 8.2) the potentiation of spontaneous motor activity produced by the NK2 receptor-selective agonist [betaAla8]NKA(4-10). 3. In sucrose-gap experiments, EFS evoked action potentials (APs) accompanied by phasic contractions of human and guinea-pig ureter, which were unaffected by tetrodotoxin or MEN 11420 (3 microM), but were blocked by nifedipine (1-10 microM). NKA (1-3 microM) produced a slow membrane depolarization with superimposed APs and a tonic contraction with superimposed phasic contractions. NKA prolonged the duration of EFS-evoked APs and potentiated the accompanying contractions. MEN 11420 completely prevented the responses to NKA in both the human and guinea-pig ureter. 4. Nifedipine (1-10 microM) suppressed the NKA-evoked APs and phasic contractions in both human and guinea-pig ureter, and slightly reduced the membrane depolarization induced by NKA. A tonic-type contraction of the human ureter in response to NKA persisted in the presence of nifedipine. 5. In conclusion, tachykinins produce smooth muscle excitation in both human and guinea-pig ureter by stimulating receptors of the NK2 type only. NK2 receptor activation depolarizes the membrane to trigger the firing of APs from latent pacemakers.

Calcitonin gene-related peptide innervation of the rat hepatobiliary system

The digestive system is densely innervated by calcitonin gene-related peptide (CGRP)-immunoreactive neurons. The present study investigated a) the distribution and origin of CGRP-immunoreactive fibers in the rat hepatobiliary tract, and b) their relation with substance P/tachykinin (SP/TK) immunoreactivity using immunohistochemical and radioimmunoassay techniques. CGRP-containing fibers form dense networks in the fibromuscular layer of the biliary tree and surrounding the portal vein. Thin, varicose fibers are present at the base of the mucosa of the ducts. In the liver, labeled fibers are restricted to the portal areas and the stromal compartment. Neonatal treatment with capsaicin, a neurotoxin for primary afferent neurons, or celiac/superior mesenteric ganglionectomy depletes CGRP-containing fibers in the biliary tract, and reduces those associated with the portal vein. In contrast, subdiaphragmatic vagotomy does not appreciably modify the density of these fibers. Radioimmunoassay studies show a reduction of CGRP-immunoreactive contents in the biliary tract and portal vein by 84% and 65%, respectively, following capsaicin treatment, and by 80% and 66%, respectively, following ganglionectomy. By contrast, CGRP concentrations in vagotomized animals are comparable to those of controls. Most CGRP-positive fibers appear to contain SP/TK immunoreactivity, as indicated by double-label studies. These results demonstrate that the rat hepatobiliary tract is prominently innervated by CGRP- and CGRP/SP/TK-immunoreactive fibers, which are likely to originate from spinal afferent neurons. The abundance of these fibers and their association with a variety of targets are in line with the involvement of these peptidergic visceral afferents in regulating hepatobiliary activities, including hemodynamic functions of the hepatic vasculature.

Opposite modulation by tachykinin (NK1) and CGRP receptors of sympathetic control of mouse vas deferens motility

Electrical field stimulation of isolated mouse vas deferens elicited sympathetic twitch whose amplitude was transiently enhanced by the selective tachykinin NK1 receptor agonist, [Sar9,Met(O2)11]substance P (0.3-30 nM), but not by selective NK2 and NK3 receptor agonists. Potentiation by [Sar9,Met(O2)11]substance P was antagonized by (+/-)-CP 96,345 [(2S,3S)-cis-2-(diphenylmethyl)-N- [(2-methoxyphenyl)-methyl]-1-azabicyclo[2.2.2]octan-3-amine] (IC50 = 0.1 microM). On the other hand, electrical field stimulation-induced contractions were inhibited by calcitonin gene-related peptide, CGRP (0.1-30 nM), and this action was reduced by its antagonist, human CGRP-(8-37) (3 microM). [Sar9,Met(O2)11]substance P (3 nM) did not affect either high-K+ or noradrenaline-induced contraction, while CGRP (3 nM) significantly reduced the noradrenaline-induced motor response. Capsaicin (1 microM) inhibited sympathetic twitches, and this effect was partially antagonized by human CGRP-(8-37). In the presence of this antagonist, capsaicin induced a short-living and (+/-)-CP 96,345-sensitive twitch enhancement. These data suggest that the sympathetic control of mouse vas deferens motility can be modulated in an opposite manner by tachykinin NK1 (prejunctionally located) and by CGRP (pre- and/or postjunctionally located) receptors.

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)

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.

Effects of inhaled capsaicin in heart-lung transplant patients and asthmatic subjects

We have studied the effects on FEV1 of inhaled capsaicin in concentrations of 3 x 10(-6) to 3 x 10(-1) mg/ml and methacholine (1 to 16 mg/ml) in 15 heart-lung transplant (HLT) patients who had undergone recent transbronchial lung biopsy to determine the relationships in chronically denervated lungs between these different forms of airway hyperreactivity and inflammation. A total of 10 normal subjects and 17 asthmatic subjects were included for comparison. Capsaicin caused bronchodilation in eight HLT patients (FEV1 rising by 6.4 to 26.8%) and bronchoconstriction in two (fall in FEV1 of 7.2 and 7.6%). By contrast, seven asthmatic subjects developed bronchoconstriction after capsaicin (fall in FEV1 5.6 to 40.4%); the remaining 10 asthmatic subjects showed no response. Bronchial hyperresponsiveness to methacholine was most evident in the asthmatic subjects, but six HLT patients demonstrated a > or = to 20% fall in FEV1 with < or = 8 mg/ml of methacholine. All normal subjects were nonresponsive to both agents, and all normal and asthmatic subjects, unlike HLT patients, coughed with capsaicin. No relationship existed between the methacholine and capsaicin responses. In the HLT patients neither form of airway responsiveness was related to the degree of inflammation seen on transbronchial lung biopsy. The results suggest that in normal subjects, although it provokes cough, inhaled capsaicin causes little airway narrowing.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical demonstration of nerves and nerve cells in human and porcine ureters

There are divergent opinions about the origin of ureteral motility. It is either a myogenic or a neutral phenomenon. Furthermore, the existence of nerve cells in the ureter is also a controversial question. In the present study we applied immunohistochemical methods to human and porcine ureters in an attempt to clarify the mattern. As neuronal markers we used anti-PGP 9.5 and anti-NSE, and as a glial marker anti-S-100. In the whole mount preparations of pig ureter we observed two neuronal plexuses on both sides of the tunica muscularis. The inner plexus consisted of both nerve bundles and nerve cells, whereas the outer one did not contain any nerve cells. In the human ureter we found a ganglion with nerve cells beneath the tunica muscularis and the tunica adventitia.

The effects of neonatal capsaicin on plasma levels and tissue contents of CGRP

Tissue contents and plasma levels of IR-CGRP were studied following administration of capsaicin to newborn rats. A depletion of > 50% of IR-CGRP content was seen in the cardiovascular tissues (e.g., heart and peripheral arteries), lungs, gastrointestinal tract (e.g., esophagus, stomach, and intestine), genitourinary tract (e.g., ureter, bladder, uterus, and penis), and in the nervous system (e.g., dorsal root and trigeminal ganglia, sciatic and trigeminal nerves, and dorsal spinal cord) in capsaicin-treated rats, in comparison with the control rat tissues (p < 0.01). These findings are compatible with the known involvement of capsaicin of the unmyelinated sensory C and A delta fibers and hence their distribution in the nervous system and other organs. Plasma IR-CGRP levels were also significantly lower in the capsaicin-treated rats throughout their life span (p < 0.001), suggesting that, at least in part, circulating CGRP is derived from the nervous system. RP-HPLC confirmed the identity of CGRP in both tissue and plasma extracts.

Substance P and calcitonin gene-related peptide in the ureter of chicken and guinea-pig: distribution, binding sites and possible functions

To elucidate the possible functional significance of sensory neuropeptides in visceral organs of mammals and birds the distribution, binding sites and the effects on ureteric peristalsis of substance P and calcitonin gene-related peptide (CGRP) were investigated in the ureter of guinea-pigs and chickens. In the guinea-pig numerous substance P and CGRP-immunoreactive fibres were located in the adventitia, smooth muscle layer, submucosa and occasionally in the epithelium. Varicose peptidergic fibres were often found on blood vessels. Binding sites for substance P were associated with blood vessels and epithelium in the following density order: venules greater than epithelium greater than arterioles. The highest density of CGRP binding sites was detected on the smooth muscle; venules and arterioles expressed moderate binding. The peristalsis frequency of the isolated ureter of the guinea-pig was increased by neurokinin A and substance P, whereas CGRP inhibited ureteric motility. In the chicken the immunoreactivity to substance P and CGRP was less pronounced. Immunoreactive fibres were found in the submucosa close to the epithelium and around ureteric ganglion cells. Correspondingly, substance P binding sites were located in the epithelium and in ureteric ganglia; however, specific CGRP binding was restricted to large blood vessels. In the chicken none of the sensory neuropeptides affected ureteric motility. Only high doses of the sensory neurotoxin capsaicin (greater than 10 microM) repeatedly produced a non-specific inhibitory effect, similar to that found in a capsaicin-desensitized guinea-pig ureter preparation. The data suggest that in the guinea-pig ureter sensory neuropeptides play a modulatory role in the regulation of ureteric motility and might have vascular and epithelial functions. In the chicken, substance P might be involved in the regulation of epithelial function and modulation of ganglionic transmission. The physiological or pathophysiological role of sensory neuropeptides and the efferent functions of afferent fibres appears to be much better developed in the guinea-pig than in the chicken.

Tachykinins and calcitonin gene-related peptide as co-transmitters in local motor responses produced by sensory nerve activation in the guinea-pig isolated renal pelvis

Electrical field stimulation of circular muscle strips from the guinea-pig isolated renal pelvis produces a frequency-dependent positive inotropic effect of the spontaneous contractions which is unaffected by atropine and guanethidine and abolished by tetrodotoxin or in vitro capsaicin desensitization. Omega conotoxin fraction GVIA markedly inhibited the response to low frequencies of stimulation but had only a partial or minor inhibitory effect at higher frequencies. Tachykinins produce a concentration-dependent positive inotropic effect, neurokinin A being more potent than substance P. On the other hand, rat alpha calcitonin gene-related peptide (CGRP) inhibited spontaneous contractions of the renal pelvis. MEN 10,376 a neurokinin A (4-10) analog, antagonized the positive inotropism produced by neurokinin A, without affecting the response to KCl, and suppressed the positive inotropic response produced by electrical field stimulation. In the presence of MEN 10,376, a negative inotropic response was produced by electrical field stimulation which was antagonized by the C-terminal fragment (8-37) of human alpha calcitonin gene-related peptide (hCGRP). hCGRP (8-37) antagonized the negative inotropic effect of exogenously administered CGRP without affecting inhibition by isoprenaline. Application of capsaicin (10 microM) produced a marked increase in the outflow of substance P-, neurokinin A- and CGRP-like immunoreactivities from the superfused guinea-pig renal pelvis. Substance P-, neurokinin A- and CGRP-like immunoreactivities were also detected in tissue extracts of the renal pelvis by radioimmunoassay. These experiments indicate that peptide release from peripheral endings of capsaicin-sensitive primary afferents represents the major type of nerve-mediated response affecting motility of the guinea-pig isolated renal pelvis. Tachykinins and CGRP act as physiological antagonists and the excitatory action of tachykinins prevails over the inhibitory action of CGRP. Local modulation of renal pelvis motility by sensory nerves could facilitate removal of irritants present in the urine, protecting the kidney during obstruction and ureteral antiperistalsis.

Calcitonin gene-related peptide (CGRP)-immunoreactive nerve plexuses in the renal pelvis and ureter of rats

The distribution of calcitonin gene-related peptide-immunoreactive nerve fibers in the renal pelvis and ureter was examined by immunohistochemistry using whole-mount preparations and cryostat sections. The patterns of innervation were contrasted between the pelvis and ureter; the immunoreactive nerve fibers in the pelvis ran parallel to the long axis of each of the circular and longitudinal muscle layers, causing a lattice-like appearance of the nerve fibers. In the ureter, the immunoreactive fibers were accumulated in the subepithelial region and the longitudinal muscle. In both the pelvis and ureter, a portion of the nerve fibers of smaller caliber showed a swollen or beaded structure; they were located in the musculature and beneath the epithelium extending for considerable distances. Ligation of the ureter caused a marked decrease in the immunoreactive nerves in the pelvis and the proximal portion of the ureter, suggesting that the axonal flow in the calcitonin gene-related peptide-containing neurons of the ureter runs towards the pelvis.

Sensory innervation of the rat kidney and ureter as revealed by the anterograde transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) from dorsal root ganglia

The sensory innervation of the rat kidney and ureter was investigated in wholemount preparations and sectioned materials by labeling the afferent nerve fibers with wheat germ agglutinin-horseradish peroxidase (WGA-HRP) transported anterogradely from dorsal root ganglia. Labeled fibers were seen in large numbers in the ureter and in the lining of the renal pelvis, where they were located in the adventitia, smooth muscle, subepithelial connective tissue, and epithelium. Most of the fibers in the ureter and ureteropelvic junctional zone traveled parallel to the long axis of the organ. In contrast, fibers in the widest part of the funnel-shape renal pelvis were oriented predominantly in a circumferential fashion. Many of the pelvic afferents were extremely fine and appeared to terminate as free nerve endings. Modest networks of labeled axons were also observed around branches of the renal artery; the greatest innervation was supplied to the distal portions of the interlobar arteries and to the arcuate arteries. Only single axons were observed around the interlobular arteries, and very few fibers were seen around afferent arterioles or near glomeruli. In contrast to the arteries, branches of the renal vein were relatively sparsely innervated. Occasional labeled fibers entered the renal cortex and formed intimate associations with renal tubules; however, the vast majority of renal tubular elements were not contacted by labeled sensory fibers. Labeled fibers were never observed in the renal medulla or in the papilla. The present study represents the first time that the sensory innervation of the kidney and ureter has been investigated by using a highly specific anterograde nerve tracing technique. The pattern of innervation demonstrated here reveals an anatomical configuration of ureteral and renal pelvic sensory nerves consistent with a role in detection of ureteral and pelvic pressure and chemical changes and a renal vascular sensory innervation that may monitor changes in renal arterial and venous pressure and chemical content. Still other renal afferent nerve endings may signal renal pain.

Relaxant effect of capsaicin in the rat gastric fundus

The effect of capsaicin was studied in precontracted longitudinal muscle strips of the rat gastric fundus. Capsaicin induced a relaxation in the concentration range 10(-7)-10(-6) M. The relaxation induced by 10(-6) M capsaicin was completely prevented by extrinsic denervation of the stomach. The adrenoceptor antagonists phentolamine and propranolol did not influence the effect of capsaicin while hexamethonium potentiated it; this potentiation was not observed with another nicotinic receptor antagonist trimethaphan. Tetrodotoxin did not have a consistent effect as it reduced the capsaicin-induced relaxation in some but not all tissues. The peptidase trypsin consistently reduced the action of capsaicin but vasoactive intestinal polypeptide (VIP) antiserum, desensitization to calcitonin gene-related peptide (CGRP), and CGRP antiserum had no influence. The neuropeptide involved in the relaxant effect of capsaicin in the rat gastric fundus has thus still to be determined.

The neurotransmitter role of calcitonin gene-related peptide in the rat and guinea-pig ureter: effect of a calcitonin gene-related peptide antagonist and species-related differences in the action of omega conotoxin on calcitonin gene-related peptide release from primary afferents

In the rat and guinea-pig isolated ureter electrical field stimulation of intrinsic nerves (10 Hz for 10 s) produces transient inhibition of evoked (20 mM KCl or 0.1-1 microM neurokinin A) rhythmic contractions by releasing transmitter(s) from peripheral endings of capsaicin-sensitive primary afferents. The C-terminal fragment of human calcitonin gene-related peptide (8-37) blocked the inhibitory effect of electrical field stimulation as well as that produced by exogenous calcitonin gene-related peptide, while leaving unaffected the inhibitory response to isoprenaline. Human calcitonin gene-related peptide (8-37) was devoid of any inhibitory activity of its own but enhanced the amplitude and frequency of KCl-evoked rhythmic contractions in the rat ureter, probably by antagonizing the inhibitory effect of endogenous calcitonin gene-related peptide released by KCl. Omega conotoxin fraction GVIA, a peptide which possesses a potent blocking activity of N-type voltage-sensitive calcium channels, prevented the inhibitory response to electrical stimulation in the guinea-pig ureter, while leaving the response unaffected in the rat ureter. Conotoxin had no effect toward the inhibition produced by exogenous calcitonin gene-related peptide indicating its prejunctional site of action, demonstrated previously in the guinea-pig ureter [Maggi et al. (1990) Neurosci, Lett. 114, 203-206]. Dermorphin, an amphibian peptide with potent agonist activity on mu-type opioid receptors, inhibited the response to electrical stimulation in the guinea-pig ureter but had no effect in the rat ureter.(ABSTRACT TRUNCATED AT 250 WORDS)

Dual effects of capsaicin on responses of the rabbit ear artery to field stimulation

1. The effects of capsaicin (Cap) on contractions of ring segments of rabbit ear artery induced by field stimulation were studied. 2. At low concentrations (0.3-3 microM) Cap caused transient enhancement and at higher concentrations (above 3 microM) inhibition of stimulation-induced contractions, without affecting noradrenaline (NA)-induced contractions. 3. In the continuous presence of high concentrations of Cap, rebound facilitation was observed after inhibition, and at this stage, Cap elicited less inhibition of the response. 4. Repeated application of Cap at 60 min intervals irreversibly desensitized the artery to the inhibitory effect of Cap. 5. Functional removal of the endothelium enhanced the facilitatory effect of low concentrations of Cap and attenuated its inhibitory effect. 6. Pretreatment with indomethacin abolished the facilitatory effect of Cap and enhanced its inhibitory effect, indicating that prostaglandins are involved in the action of Cap. The effect of indomethacin was more marked in preparations from which the endothelium had been removed. 7. Desensitization to substance P (SP) or substance K (SK), did not affect either the inhibitory or the facilitatory effect of Cap. 8. These results suggest that the dual effects of Cap on stimulation-induced contractions of rabbit ear artery may arise from the release of multiple mediators that act prejunctionally to modulate NA release. The stimulant effect seems to be mediated by prostanoids, while the inhibitory effect seems to be caused by a substance(s) that is not SP or SK. The possibility that the mediator is calcitonin gene-related peptide requires further study.

Neuropeptide Y: presence in sympathetic and parasympathetic innervation of the nasal mucosa

The occurrence of neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP) and peptide histidine isoleucine (PHI) in the sympathetic and parasympathetic innervation of the nasal mucosa was studied in various species including man. A dense network of NPY-immunoreactive (IR) fibres was present around arteries and arterioles in the nasal mucosa of all species studied. NPY was also located in nerves around seromucous glands in pig and guinea-pig, but not in rat, cat and man. The NPY-IR glandular innervation corresponded to about 20% of the NPY content of the nasal mucosa as revealed by remaining NPY content determined by radioimmunoassay after sympathectomy. These periglandular NPY-positive fibres had a distribution similar to the VIP-IR and PHI-IR nerves but not to the noradrenergic markers tyrosine hydroxylase (TH) or dopamine-beta-hydroxylase (DBH). The NPY nerves around glands and some perivascular fibres were not influenced by sympathectomy and probably originated in the sphenopalatine ganglion where NPY-IR and VIP-IR ganglion cells were present. The venous sinusoids were innervated by NPY-positive fibres in all species except the cat. Dense NPY and DBH-positive innervation was seen around thick-walled vessels in the pig nasal mucosa; the latter may represent arterio-venous shunts. Double-labelling experiments using TH and DBH, and surgical sympathectomy revealed that the majority of NPY-IR fibres around blood vessels were probably noradrenergic. The NPY-positive perivascular nerves that remained after sympathectomy in the pig nasal mucosa also contained VIP/PHI-IR. The major nasal blood vessels, i.e. sphenopalatine artery and vein, were also densely innervated by NPY-IR fibres of sympathetic origin. Perivascular VIP-IR fibres were present around small arteries, arterioles, venous sinusoids and arterio-venous shunt vessels of the nasal mucosa whereas major nasal vessels received only single VIP-positive nerves. The trigeminal ganglion of the species studied contained only single TH-IR or VIP-IR but no NPY-positive ganglion cells. It is concluded that NPY in the nasal mucosa is mainly present in perivascular nerves of sympathetic origin. In some species, such as pig, glandular and perivascular parasympathetic nerves, probably of VIP/PHI nature, also contain NPY.

Effect of capsaicin on gastric corpus smooth muscle of the rat in vitro

Circular strips of the rat gastric corpus muscle were mounted in Krebs solution for isometric tension recording. Addition of capsaicin usually led to either relaxation or contraction, but in some strips a biphasic response was observed. Although no clear-cut concentration-response relationship could be established, capsaicin predominantly induced contraction at 500 nM, whereas at 5 microM it mainly induced relaxation. In Krebs solution containing atropine plus guanethidine, the contraction induced by 500 nM capsaicin was significantly reduced. The contraction induced by capsaicin was abolished by spantide, a tachykinin antagonist, or by tachyphylaxis to substance P. Calcitonin gene-related peptide relaxed gastric smooth muscle, however, a dose-response relationship could not be established. This peptide contracted the muscle strips only at 1 microM. Tachyphylaxis to calcitonin gene-related peptide did not significantly influence the action of capsaicin. Vasoactive intestinal polypeptide dose dependently relaxed gastric corpus strips; however, these responses were qualitatively different from those to capsaicin. It is concluded that capsaicin contracts rat gastric smooth muscle via the release of tachykinins; cholinergic interneurones are involved. The mediator of the capsaicin-induced relaxation has yet to be determined.

Regulation of epithelial transport in the jejunal mucosa of the guinea pig by neurokinins

This study characterizes the actions of the neurokinins and calcitonin-gene related peptide (CGRP) on electrolyte transport across the mucosa of the guinea pig jejunum in vitro in a modified Ussing chamber. By following changes in short circuit current (Isc) induced by substance P (SP) and neurokinins A & B (NKA & NKB) in the presence and absence of tetrodotoxin (TTX) and atropine, it was established that two distinct neurokinin receptors are involved in the regulation of electrolyte transport. NKA preferentially activates a neuronal receptor since the actions of this neurokinin were inhibited by both TTX and atropine. SP, whose actions were reduced to a lesser extent by TTX and atropine, is considered to activate preferentially a receptor on the epithelial cells. The third neurokinin, NKB, appears to act non-selectively on both the neuronal and epithelial receptors. CGRP, which per se did not affect Isc, markedly potentiated the increases in Isc induced by SP and NKB, and thus acts synergistically with the epithelial neurokinin receptor. These results suggest that two distinct neurokinin receptors (the NK-1 and the NK-2) regulate epithelial transport in the jejunal mucosa of the guinea pig, and furthermore indicate that at least one of the peptides found in enteric nerves (i.e. CGRP) modulates the actions of neurokinins on epithelial cells.

Stimulation of afferent fibres of the guinea-pig ureter evokes potentials in inferior mesenteric ganglion neurones

1. Intracellular recordings were made from neurones of the guinea-pig inferior mesenteric ganglion (IMG) maintained in vitro with both ureters and major nerve trunks attached. Afferent fibres in the ureteric nerve were activated by electrical, chemical and mechanical stimuli. 2. Repetitive stimulation of a ureteric nerve branch evoked a non-cholinergic, synaptic slow excitatory potential (slow EPSP) in 48% of neurons. The amplitude of the slow EPSP was dependent on membrane potential and was decreased by membrane depolarization and increased by hyperpolarization. 3. The slow EPSP was attenuated or abolished by capsaicin (1 microM), which itself depolarized IMG neurones. Substance P (2 microM) or neurokinin A (2 microM) also depolarized IMG neurones and in the presence of these tachykinins the slow EPSP was attenuated or abolished. 4. Distension of the ureter evoked a non-cholinergic slow depolarization in 45% of IMG neurones which was abolished by tetrodotoxin (1 microM) and by capsaicin (1 microM). 5. Chemical stimulation of ureteric afferent nerve terminals by intralumenal perfusions of the ureter with capsaicin (1 microM) produced a slow depolarization in the IMG which was prevented by blocking nerve conduction with TTX. 6. These data demonstrate that electrical stimulation of ureteric afferent fibres produces a non-cholinergic slow EPSP in the IMG. Primary afferent (capsaicin-sensitive) C fibres are also activated by distension of the ureter and evoke a slow depolarization in the IMG. The synaptic mediator of these events is likely to be tachykinin(s) released from capsaicin-sensitive C fibres. These fibres may be mechanosensory and/or nociceptive.

Secretion, pain and sneezing induced by the application of capsaicin to the nasal mucosa in man

1. Topical application of capsaicin to the human nasal mucosa induced a burning sensation and sneezing. A dose-dependent seromucous nasal secretion was also observed. Capsaicin (75 micrograms) was more potent than methacholine (50 mg) in producing nasal secretion, while topical histamine (200 micrograms), substance P (135 micrograms) and calcitonin gene-related peptide (36 micrograms) did not induce rhinorrhea. 2. Pretreatment with either topical ipratropium bromide, systemic dexchlorpheniramine or indomethacin did not influence the effects induced by capsaicin. Topical pretreatment with lidocaine inhibited the painful sensation but failed to block the rhinorrhea. Desensitization to the effects of capsaicin occurred following 4-5 subsequent applications, and full recovery was observed within 30-40 days. 3. It is proposed that the effects of capsaicin in human nasal mucosa are due to excitation of primary afferent neurones that (a) convey burning and painful sensation, (b) evoke a sneezing reflex and (c) induce nasal secretion by releasing transmitter(s) from their peripheral terminals.

Actions of neuropeptide K and calcitonin gene-related peptide on inferior mesenteric ganglion cells--tachykinin interactions with non-cholinergic potentials evoked by ureteric nerve stimulation

Neuropeptide K (NPK) induced a slow depolarization in principal ganglion cells of the guinea pig inferior mesenteric ganglion (IMG) in vitro. This effect was due to a postsynaptic action and prevented by pre-exposure of the IMG to neurokinin A (NKA) or substance P (SP). The non-cholinergic slow postsynaptic excitatory potential (s-EPSP) evoked by ureteric nerve stimulation was depressed during NPK, SP or NKA application. Calcitonin gene-related peptide (CGRP) applied in concentrations up to 10 microM had no effect on the membrane potential in 90% of IMG cells nor did it influence the s-EPSP. We suggest that NPK may depolarize IMG neurones via similar mechanisms/in a similar fashion, to other tachykinins and that the s-EPSP, induced by stimulation of the afferent ureteric nerve fibres, is mediated by a tachykinin whereas there is little indication/evidence for an involvement of CGRP.

Calcitonin gene-related peptide: release by capsaicin and prolongation of the action potential in the guinea-pig heart

The mechanisms underlying the stimulatory effects of capsaicin on the contractility of the guinea-pig heart were studied in vitro. Capsaicin (10(-7) to 10(-5) M) caused an increased overflow of immunoreactive material, suggesting release of calcitonin gene-related peptide (CGRP)-and neurokinin A (NKA)-like immunoreactivity (-LI), but not of neuropeptide Y (NPY)-LI from the isolated Langendorff-perfused whole heart. The capsaicin-induced release was calcium-dependent. During exposure to capsaicin, the heart rate was increased, while the contractile force was reduced. In addition to releasing CGRP and NKA-LI, potassium (60 mM) also increased the overflow of NPY-LI. The potassium-induced release of peptides was less calcium-dependent than the response to capsaicin. Considerably higher tissue levels of CGRP-LI were found in the atria (about 30 pmol g-1) than in the ventricles (about 10 pmol g-1). In experiments on the right atria using transmembrane action-potential recordings of myocytes, CGRP induced a prolongation of the action potential concomitantly with an increase in rate and contractile force, which was similar to the effect of noradrenaline. Furthermore, CGRP increased the contractile force and relaxation velocity of the electrically stimulated atria. Capsaicin (10(-7) M) also increased the duration of the atrial action potential. In conclusion, CGRP-like material is released by capsaicin from the isolated guinea-pig heart. Both CGRP and capsaicin prolong the plateau phase of the action potential of atrial myocytes. Therefore, the present data give further evidence that CGRP release from sensory nerves within the heart underlies the cardiostimulatory actions of capsaicin.

The sensory-efferent function of capsaicin-sensitive sensory neurons

Capsaicin-sensitive sensory neurons convey to the central nervous system signals (chemical and physical) arising from viscera and the skin which activate a variety of visceromotor and neuroendocrine reflexes integrated at various levels (intramurally in peripheral organs, at level of prevertebral ganglia, spinal and supraspinal level). Much evidence is now available that peripheral terminals of certain sensory neurons, widely distributed in skin and viscera have the ability to release, upon adequate stimulation, their transmitter content. In addition to the well-known "axon reflex" arrangement, the capsaicin-sensitive sensory neurons have the ability to release the stored transmitter also from the same terminal which is excited by the environmental stimulus. The efferent function of these sensory neurons is realized through the direct and indirect (i.e. mediated by activation of other cells) effects of released mediators. The action of released transmitters on postjunctional elements covers a wide range of effects which may have a physiological or pathological relevance. Development of drugs capable of controlling the sensory-efferent functions of the capsaicin-sensitive sensory neurons represent a new and very promising area of research for pharmacological treatment of various human diseases.

Pharmacological action of nicotine in the isolated urinary bladder from rabbit: special reference to the chronic nicotine treatment

1. A mode of action of nicotine and a change of the responsiveness to nicotine following chronic nicotine treatment in the urinary bladder of rabbit were investigated. 2. Nicotine induced only a contraction in the urinary bladder of rabbit, and the response to nicotine was reduced by hexamethonium, atropine and capsaicin. These findings suggest that the contractile response to nicotine was mediated through an action on the nicotinic receptors and partially due to the release of acetylcholine and tachykinins. 3. Tetrodotoxin did not inhibit the contractile response to nicotine in the rabbit detrusor muscle, suggesting that the nicotine-induced response may be produced mainly through a sodium action potential-independent process. 4. Nicotine-induced contraction was reduced following the chronic nicotine treatment without a change of its pharmacological properties. These findings suggest that chronic nicotine treatment might cause a decrease of the amounts of nicotinic receptors and also receptors for mediators released by nicotine.

Two types of relaxation due to capsaicin in the guinea pig isolated ileum

The relaxant effect of capsaicin was investigated on isolated segments of guinea pig ileum precontracted by histamine. Two types of relaxation could be distinguished. Low concentrations of capsaicin (0.033-3.3 microM) caused partial relaxation (type I) which was prevented by in vitro desensitization to capsaicin or by extrinsic denervation and reduced by tachyphylaxis to calcitonin gene-related peptide. At higher concentrations (10-100 microM) capsaicin caused relaxation (type II) to the baseline; this effect was insensitive to capsaicin desensitization or extrinsic denervation. Neither type of relaxation was inhibited by tetrodotoxin or by alpha- and beta-adrenoceptor antagonists. We suggest that type I relaxation results from a specific effect of capsaicin on extrinsic sensory neurones of the gut while type II represents a non-specific smooth muscle depressant effect. Intrinsic enteric neurones are not involved in these effects.

Capsaicin enhances the non-adrenergic twitch response of rat vas deferens

1 Capsaicin (Cap) enhanced the twitch response of the epididymal and prostatic portions of rat vas deferens induced by field stimulation at 0.1 Hz. The effect of Cap was reproducible and showed no desensitization. 2 Prazosin, and pretreatment with reserpine or Cap did not affect the potentiating effect of Cap, whereas pretreatment with 6-hydroxydopamine abolished the action of Cap. 3 Cap tended to attenuate the contractions induced by noradrenaline, tyramine and ATP. 4 Like Cap, substance K and substance P augmented the twitch response without causing desensitization, but their effects differed somewhat from that of Cap. Calcitonin gene-related peptide inhibited the twitch response. 5 These results suggest that Cap enhances a stimulation-induced, prazosin-resistant non-adrenergic twitch response of rat vas deferens through an as yet undefined prejunctional mechanism. This mechanism is possibly mediated by some peptide released in response to Cap from sensory neurones, which in turn acts on sympathetic nerves and increases stimulation-induced release of a mediator or cotransmitter responsible for the non-adrenergic twitch response. However, the possibility that Cap has a direct action on sympathetic nerves cannot be ruled out.

Bronchoconstrictor and hypotensive effects in relation to pharmacokinetics of tachykinins in the guinea-pig--evidence for extraneuronal cleavage of neuropeptide K to neurokinin A

1. The biological effects of the tachykinins substance P (SP), neurokinin A (NKA) and neuropeptide K (NPK) were studied in relation to their pharmacokinetic properties in the guinea-pig in vivo. 2. NKA and NPK exerted a considerably larger bronchoconstrictor effect than SP. The effect of NPK was slow in onset and had a long duration. The three tachykinins showed similar hypotensive effects although NPK had a longer duration of action than SP and NKA. 3. The disappearance of NPK-like immunoreactivity (-LI) from plasma after i.v. infusion of synthetic NPK was biphasic with apparent half-lives of 0.9 min and 6 min. The plasma half-life of NKA-LI was less than 2 min, while plasma SP-LI was degraded before biochemical analysis could be performed. 4. In guinea-pig plasma at 37 degrees C in vitro, NKA- and NPK-LI were stable for 10 min, while SP-LI disappeared with a half-life of 10 s. 5. Reversed phase HPLC analysis of plasma collected after an i.v. infusion of NPK for 25 min, indicated a partial cleavage of NPK into NKA. 6. It is concluded that potency of the biological effects of SP, NKA and NPK in the guinea-pig in vivo, may not only be attributed to activation of multiple tachykinin receptors but must also be related to the marked differences in pharmacokinetical properties between the tachykinins. Furthermore, whereas SP is rapidly degraded in plasma, NKA and NPK seem to be metabolized in other compartments.

Neuropeptides in pelvic afferent pathways

Neurochemical and pharmacological experiments have raised the possibility that several neuropeptides including, vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine amide (PHI), substance P, calcitonin gene-related peptide (CGRP), neurokinin A, cholecystokinin (CCK) and opioid peptides may be transmitters in afferent pathways to the pelvic viscera. These substances are widely distributed in: 1) nerve fibers in the pelvic organs, 2) visceral afferent neurons in the lumbosacral dorsal root ganglia and 3) at sites of afferent termination in the spinal cord. Double staining immunocytochemical techniques have shown that more than one peptide can be localized in individual visceral afferent neurons and that neuronal excitatory (VIP, substance P, CCK) and inhibitory peptides (leucine enkephalin) can coexist in the same afferent cell. Studies with the neurotoxin, capsaicin, indicate that peptidergic afferent pathways are involved in the initiation of central autonomic reflexes as well as peripheral axon reflexes which modulate smooth muscle activity, facilitate transmission in automatic ganglia and trigger local inflammatory responses.

Calcitonin gene-related peptide (CGRP) in capsaicin-sensitive substance P-immunoreactive sensory neurons in animals and man: distribution and release by capsaicin

The presence of calcitonin-gene related peptide (CGRP)-like immunoreactivity (-LI) in sensory neurons was established by immunohistochemistry and radioimmunoassay (RIA) in combination with high performance liquid chromatography (HPLC). CGRP-immunoreactive (-IR) nerve fibres were present in many peripheral organs including heart, ureter, uterus and gall bladder of guinea-pig and man. The distribution of CGRP-IR nerves in the dorsal horn of the spinal cord, of positive cell bodies in thoracic spinal and nodose ganglia and nerves in peripheral organs was closely related to that of substance P-LI. Double staining experiments revealed that in most cases peripheral CGRP-IR nerve terminals also contained SP-LI. However, different localization of SP- and CGRP-IR neurons was observed in the nucleus of the solitary tract as well as in the ventral horn of the spinal cord. In the heart, CGRP-IR nerves were associated with myocardial cells (mainly atria), coronary vessels, local parasympathetic ganglia as well as with the epi- and endocardia. Three to 4-fold higher levels of native CGRP-LI were observed in the atria than in the ventricles of the heart. HPLC analysis revealed that the major peak of CGRP-LI in the heart of rat and man had the same retention times as the synthetic equivalents. Systemic capsaicin pretreatment and adult guinea-pigs caused a loss of CGRP-IR terminals in the dorsal horn of the spinal cord as well as in peripheral organs including the heart. After capsaicin treatment, the content of CGRP-IR was reduced by 70% in the heart and by 60% in the dorsal part of the spinal cord. In superfusion experiments with slices from the rat spinal cord, a release of CGRP-LI was induced by 60 mM K+ and 3 microM capsaicin in a calcium-dependent manner.