Role Of Muscarinic Acetylcholine Receptors Research Articles

M1/M3 and M2/M4 muscarinic receptor double-knockout mice present distinct respiratory phenotypes

We investigated the role of muscarinic acetylcholine receptors in the control of breathing. Baseline breathing at rest and ventilatory responses to brief exposures to hypoxia (10% O(2)) and hypercapnia (3% and 5% CO(2)), measured by whole-body plethysmography in partially restrained animals, were compared in mice lacking either M(1) and M(3) or M(2) and M(4) muscarinic receptors, and in wild-type matched controls. M(1/3)R double-knockout mice showed at rest an elevated ventilation (V (E)) due to a large (57%) increase in tidal volume (V(T)). Chemosensory ventilatory responses were unaltered. M(2/4)R double-knockout mice were agitated and showed elevated V (E) and breathing frequency (f(R)) at rest when partially restrained, but unaltered V (E) and low f(R) when recorded unrestrained. Chemosensory ventilatory responses were unaltered. The results suggest that M(1) and M(3) receptors are involved in the control of tidal volume, while M(2) and M(4) receptors may be involved in the control of breathing frequency at rest and response to stress.

Differential signalling pathways involved in cholinoceptor‐dependent stimulation of nitric oxide isoforms in dental pulp

To investigate the role of muscarinic acetylcholine receptor (mAChR) subtype activity in the regulation of endothelial- (e) and neuronal- (n) nitric oxide synthase (NOS) expression and activity. Rat dental pulp tissue was used throughout the study. The e-nos and n-nos mRNA levels were specifically measured using reverse transcriptase polymerase chain reaction procedures that involve simultaneous co-amplification of both target cDNA and a reference template with a single set of primers. NOS activity was measured by the production of [U-(14)C]-citrulline from [U-(14)C]-arginine. Stimulation of M(1)/M(2) and M(3)/M(4) mAChRs with pilocarpine caused an increase in e-nos and n-nos mRNA levels and NOS activity in the dental pulp. The specific mAChR subtype antagonists, L-NMMA, l-NIO and N(2)-propyl-L-arginine but not aminoguanidine attenuated all these effects. Inhibitors of phospholipase C (PLC), protein kinase C (PKC) and calcium/calmodulin (CaM) prevented the pilocarpine-dependent increase in n-nos and e-nos mRNA levels and NOS activity. Activation of mAChR subtypes stimulated NOS activity by increasing the production of NO through e-nos and n-nos gene expression and NOS activity. The mechanism appears to occur secondarily to stimulation of CaM and PKC enzymatic activity.

Functional roles of muscarinic M 2 and M 3 receptors in mouse stomach motility: Studies with muscarinic receptor knockout mice

Functional roles of muscarinic acetylcholine receptors in the regulation of mouse stomach motility were examined using mice genetically lacking muscarinic M 2 receptor and/or M 3 receptor and their corresponding wild-type (WT) mice. Single application of carbachol (1 nM–30 μM) produced concentration-dependent contraction in antral and fundus strips from muscarinic M 2 receptor knockout (M 2R-KO) and M 3 receptor knockout (M 3R-KO) mice but not in those from M 2 and M 3 receptors double knockout (M 2/M 3R-KO) mice. A comparison of the concentration–response curves with those for WT mice showed a significant decrease in the negative logarithm of EC 50 (pEC 50) value (M 2R-KO) or amplitude of maximum contraction (M 3R-KO) in the muscarinic receptor-deficient mice. The tonic phase of carbachol-induced contraction was decreased in gastric strips from M 3R-KO mice. Antagonistic affinity for 4-diphenylacetoxy- N-methyl-piperidine (4-DAMP) or 11-([2-[(diethylamino)methyl]-1-piperdinyl]acetyl)-5,11-dihydro-6H-pyrido[2,3-b][1,4]benzodiazepine-6-one (AF-DX116) indicated that the contractile responses in M 2R-KO and M 3R-KO mice were mediated by muscarinic M 3 and M 2 receptors, respectively. Electrical field stimulation (EFS, 0.5–32 Hz) elicited frequency-dependent contraction in physostigmine- and N ω-nitro- l-arginine methylester ( l-NAME)-treated fundic and antral strips from M 2R-KO and M 3R-KO mice, but the cholinergic contractile components decreased significantly compared with those in WT mice. In gastric strips from M 2/M 3R-KO mice, cholinergic contractions elicited by EFS were not observed but atropine-resistant contractions were more conspicuous than those in gastric strips from WT mice. Gastric emptying in WT mice and that in M 2/M 3R-KO mice were comparable, suggesting that motor function of the stomach in the KO mice did not differ from that in the WT mice. The results indicate that both muscarinic M 2 and M 3 receptors but not other subtypes mediate carbachol- or EFS-induced contraction in the mouse stomach but that the contribution of each receptor to concentration–response relationships is distinguishable. Although there was impairment of nerve-mediated cholinergic responses in the stomach of KO mice, gastric emptying in KO mice was the same as that in WT mice probably due to the compensatory enhancement of the non-cholinergic contraction pathway.

Muscarinic cholinoceptor activation modulates DNA synthesis and CD40 expression in fibroblast cells

1 The aim of the present work was to examine the role of muscarinic acetylcholine receptors (mAChR) on DNA synthesis and CD40 expression in human fibroblast cells. Neonatal human skin fibroblast cultures were stimulated with carbachol in presence or absence of specific antagonists and the following parameters were measured: identification of mAChR subtypes, DNA synthesis, inositol phosphates (InsP) production and CD40 expression. 2 Human fibroblasts express mAChR with Kd 0.47 +/- 0.11 nm and Bmax 236 +/- 22 fmol mg protein(-1). Carbachol stimulates DNA synthesis, InsP and the expression of CD40. All these effects were inhibited by atropine, mustard hydrochloride (4-DAMP) and pirenzepine but not by AF-DX 116 and tropicamide, indicating that M3 and M1 mAChR are implicated in carbachol action. The relative Ki of the antagonists obtained by competition binding assay was in parallel to the relative potency for blocking both carbachol-stimulated InsP accumulation and DNA synthesis. 3 The intracellular pathway leading to carbachol-induced biological effects involved phospholipase C and calcium/calmodulin, as U-73122 and trifluoroperazine blocked carbachol effects, respectively. Calphostin C, a protein kinase C inhibitor, had no effect, indicating that this enzyme does not participate in the system. 4 These results may contribute to a better understanding of the modulatory role of the parasympathetic muscarinic system on normal human fibroblast function.

A critical role for β cell M 3 muscarinic acetylcholine receptors in regulating insulin release and blood glucose homeostasis in vivo

One of the hallmarks of type 2 diabetes is that pancreatic beta cells fail to release sufficient amounts of insulin in the presence of elevated blood glucose levels. Insulin secretion is modulated by many hormones and neurotransmitters including acetylcholine, the major neurotransmitter of the peripheral parasympathetic nervous system. The physiological role of muscarinic acetylcholine receptors expressed by pancreatic beta cells remains unclear at present. Here, we demonstrate that mutant mice selectively lacking the M3 muscarinic acetylcholine receptor subtype in pancreatic beta cells display impaired glucose tolerance and greatly reduced insulin release. In contrast, transgenic mice selectively overexpressing M3 receptors in pancreatic beta cells show a profound increase in glucose tolerance and insulin release. Moreover, these mutant mice are resistant to diet-induced glucose intolerance and hyperglycemia. These findings indicate that beta cell M3 muscarinic receptors play a key role in maintaining proper insulin release and glucose homeostasis.

Inducible nitric oxide synthase subserves cholinergic vasodilation in retina

In this paper, we investigate the role of muscarinic acetylcholine receptor (mAChR) activity in the regulation of inducible (i) nitric oxide synthase (iNOS) expression and activity. The signaling pathway involved is also examined. These experiments also provide a link between mAChR activation and the nitric oxide (NO)-dependent regulation of retinal vascular diameter. The diameter of the retinal vessels at a distance of 1 disc diameter from the center of the optic disc was measured in rats using digital retinal photography, and both iNOS-mRNA gene expression and NOS were specifically measured using RT-PCR and [U-(14)C] citrulline assays, respectively. Stimulation of M(1) and M(3) mAChR with carbachol caused an increase in vessel diameter, in iNOS-mRNA levels and in NOS activity in the retina. Aminoguanidine, an inhibitor of iNOS, attenuated all these effects. Inhibitors of phospholipase C (PLC) and protein kinase C (PKC) but not calcium/calmodulin (CaM) prevented the muscarinic-dependent increase in iNOS-mRNA levels. The results obtained suggest that the activation of mAChR increases retinal vessel diameters by increasing the production of nitric oxide (NO) through iNOS activation and iNOS-mRNA gene expression. The mechanism appears to occur secondarily to stimulation of PLC and PKC enzymatic activity.

Muscarinic modulation of the trigemino-reticular pathway in lampreys.

In lampreys, reticulospinal neurons integrate sensory inputs to adapt their control onto the spinal locomotor networks. Whether and how sensory inputs to reticulospinal neurons are modulated remains to be determined. We showed recently that cholinergic inputs onto reticulospinal neurons play a key role in the initiation of locomotion elicited by stimulation of the mesencephalic locomotor region in semi intact lampreys. Here, we examined the possible role of muscarinic acetylcholine receptors in modulating trigeminal inputs to reticulospinal neurons. A local application of muscarinic agonists onto an intracellularly recorded reticulospinal cell depressed the disynaptic responses to trigeminal stimulation. A depression was also observed when muscarinic agonists were pressure ejected over the brain stem region containing second-order neurons relaying trigeminal inputs to reticulospinal neurons. Conversely, muscarinic antagonists increased the trigeminal-evoked responses, suggesting that a muscarinic depression of sensory inputs to RS neurons is exerted tonically. The muscarinic modulation affected predominantly the N-methyl-d-aspartate (NMDA) component of the trigeminal-evoked responses. Moreover, atropine perfusion facilitated the occurrence of sustained depolarizations induced by stimulation of the trigeminal nerve, and it revealed NMDA-induced intrinsic oscillations in reticulospinal neurons. The functional significance of a muscarinic modulation of a sensory transmission to reticulospinal neurons is discussed.

Radiation hybrid mapping of five muscarinic acetylcholine receptor subtype genes in Rattus norvegicus

Acetylcholine is the main neurotransmitter of the vestibular efferent system and a wide variety of muscarinic and nicotinic acetylcholine receptors are expressed in the vestibular periphery. The role of these receptors and in particular the role of muscarinic acetylcholine receptors in the physiology of the vestibular neuroepithelium is not understood. Congenic and consomic rats are a convenient way to investigate the involvement of candidate genes in the manifestation of defined traits. To use congenic or consomic rats to elucidate the roles of these receptors in vestibular physiology or pathology the chromosomal location of the genes encoding these receptors has to be determined. Using radiation hybrid (RH) mapping and a rat RH map server ( www.rgd.mcw.edu/RHMAP SERVER/), we determined the chromosomal locations of the muscarinic acetylcholine receptor genes in the rat ( Rattus norvegicus). The m1–m5 muscarinic subtypes mapped to the following chromosomes: Chrm1, chromosome 1; Chrm2, chromosome 4; Chrm3, chromosome 17; Chrm4, chromosome 3; and Chrm5, chromosome 3. With the chromosomal location for each of these muscarinic subtypes known, it is now possible to develop congenic and consomic strains of rats that can be used to study the functions of each of these subtypes.

Contribution of cholinergic systems to state-dependent modulation of respiratory control.

Respiration is altered during different stages of the sleep-wake cycle. We review the contribution of cholinergic systems to this alteration, with particular reference to the role of muscarinic acetylcholine receptors (MAchRs) during rapid eye movement (REM) sleep. Available evidence demonstrates that MAchRs have potent excitatory effects on medullary respiratory neurones and respiratory motoneurones, and are likely to contribute to changes in central chemosensitive drive to the respiratory control system. These effects are likely to be most prominent during REM sleep, when cholinergic brainstem neurones show peak activity levels. It is possible that MAchR dysfunction is involved in sleep-disordered breathing, such as obstructive sleep apnea.

Role of muscarinic acetylcholine receptors in a guinea pig model of asthma

We examined the density of muscarinic acetylcholine receptor (mACh-R) subtypes (M1R, M2R and M3R) in guinea pig lung. The density of M3R in the lung tissue of ovalbumin (OA)-sensitized guinea pigs was higher than that in the control group. However, no difference was observed in the affinity of M3R between the sensitized and the control lungs. No difference was observed in the density and affinity of M1R and M2R in sensitized and control lungs. Pilocarpine, which is an M2R stimulant, increased the density of M3R in the lung tissue and the rate of the increase in sensitized guinea pigs was less than that in the control group. In contrast, methoctranine, which is an M2R antagonist, decreased the density of M3R and the rate of this decrease was the same in the sensitized and control groups. These results suggest that, in OA-sensitized guinea pigs, a dysfunction of M2R leads to the abnormal density of M3R.

Muscarinic receptor knockout mice: role of muscarinic acetylcholine receptors M(2), M(3), and M(4) in carbamylcholine-induced gallbladder contractility.

Muscarinic receptors play a major role in gallbladder function, although the muscarinic receptor(s) mediating smooth muscle contractility is unclear. This study compared smooth muscle contractile responses to carbamylcholine (10(-7)-10(-3) M) in isolated gallbladder from wild-type and M(2), M(3), and M(4) receptor knockout mice. Carbamylcholine-induced contraction in gallbladder was associated with tachyphylaxis and the release of a cyclooxygenase product because indomethacin (10(-6) M) inhibited carbamylcholine-induced contraction. The M(3) receptor was the major muscarinic receptor involved in contraction because carbamylcholine-induced contractility was inhibited in gallbladder from M(3) receptor knockout mice. Furthermore, the muscarinic receptor antagonists 11-[[[2-diethylamino-O-methyl]-1-piperidinyl]acetyl]-5,11-dihydrol-6H-pyridol[2,3-b][1,4]benzodiazepine-6-one (AF-DX 116) and pirenzepine dextrally shifted contraction to carbamylcholine in gallbladder from wild-type, M(2), and M(4) receptor knockout mice, with affinities consistent with M(3) receptor interaction. In addition, maximal contraction to carbamylcholine was reduced in gallbladder from M(2) receptor knockout mice and affinities for AF-DX 116 and pirenzepine in gallbladder from M(3) receptor knockout mice were consistent with their affinities at M(2) receptors. In M(4) receptor knockout mice, contraction to carbamylcholine was dextrally shifted, although the affinities for AF-DX 116 and pirenzepine in gallbladder from M(2) or M(3) knockout mice were not similar to their affinities at M(4) receptors. The M(4) receptor may serve as an accessory protein necessary for optimal potency of M(2) and M(3) receptor-mediated responses. Thus, muscarinic receptor knockout mice provided direct and unambiguous evidence that M(3), and to a lesser extent, M(2) receptors are the predominant muscarinic receptors mediating gallbladder contractility, and M(4) receptors appear necessary for optimal potency of carbamylcholine in gallbladder contraction.

MAChRs in the grasshopper brain mediate excitation by activation of the AC/PKA and the PLC second-messenger pathways.

The species-specific sound production of acoustically communicating grasshoppers can be stimulated by pressure injection of both nicotinic and muscarinic agonists into the central body complex and a small neuropil situated posterior and dorsal to it. To determine the role of muscarinic acetylcholine receptors (mAChRs) in the control of acoustic communication behavior and to identify the second-messenger pathways affected by mAChR-activation, muscarinic agonists and membrane-permeable drugs known to interfere with specific mechanisms of intracellular signaling pathways were pressure injected to identical sites in male grasshopper brains. Repeated injections of small volumes of muscarine elicited stridulation of increasing duration associated with decreased latencies. This suggested an accumulation of excitation over time that is consistent with the suggested role of mAChRs in controlling courtship behavior: to provide increasing arousal leading to higher intensity of stridulation and finally initiating a mating attempt. At sites in the brain where muscarine stimulation was effective, stridulation could be evoked by forskolin, an activator of adenylate cyclase (AC); 8-Br-cAMP-activating protein kinase A (PKA); and 3-isobuty-1-methylxanthine, leading to the accumulation of endogenously generated cAMP through inhibition of phosphodiesterases. This suggested that mAChRs mediate excitation by stimulating the AC/cAMP/PKA pathway. In addition, muscarine-stimulated stridulation was inhibited by 2'-5'-dideoxyadenonsine and SQ 22536, two inhibitors of AC; H-89 and Rp-cAMPS, two inhibitors of PKA; and by U-73122 and neomycin, two agents that inhibit phospholipase C (PLC) by independent mechanisms. Because the inhibition of AC, PKA, or PLC by various individually applied substances entirely suppressed muscarine-evoked stridulation in a number of experiments, activation of both pathways, AC/cAMP/PKA and PLC/IP(3)/diacylglycerine, appeared to be necessary to mediate the excitatory effects of mAChRs. With these studies on an intact "behaving" grasshopper preparation, we present physiological relevance for mAChR-evoked excitation mediated by sequential activation of the AC- and PLC-initiated signaling pathways that has been reported in earlier in vitro studies.

A role for muscarinic excitation: control of specific singing behavior by activation of the adenylate cyclase pathway in the brain of grasshoppers.

Muscarinic acetylcholine receptors exert slow and prolonged synaptic effects in both vertebrate and invertebrate nervous systems. Through activation of G proteins, they typically decrease intracellular cAMP levels by inhibition of adenylate cyclase or stimulate phospholipase C and the turnover of inositol phosphates. In insects, muscarinic receptors have been credited with two main functions: inhibition of transmitter release from sensory neuron terminals and regulation of the excitability of motoneurons and interneurons. Our pharmacological studies with intact and behaving grasshoppers revealed a functional role for muscarinic acetylcholine receptors as being the basis for specific arousal in defined areas of the brain, underlying the selection and control of acoustic communication behavior. Periodic injections of acetylcholine into distinct areas of the brain elicited songs of progressively increasing duration. Coinjections of the muscarinic receptor antagonist scopolamine and periodic stimulations with muscarine identified muscarinic receptor activation as being the basis for the underlying accumulation of excitation. In contrast to reports from other studies on functional circuits, muscarinic excitation was apparently mediated by activation of the adenylate cyclase pathway. Stimulation of adenylate cyclase with forskolin and of protein kinase A with 8-Br-cAMP mimicked the stimulatory effects of muscarine whereas inhibition of adenylate cyclase with SQ22536 and of protein kinase A with H-89 and Rp-cAMPs suppressed muscarine-stimulated singing behavior. Activation of adenylate cyclase by muscarinic receptors has previously been reported from studies on membrane preparations and heterologous expression systems, but a physiological significance of this pathway remained to be demonstrated in an in vivo preparation.

The Non-neuronal Cholinergic System: Roles of Muscarinic Acetylcholine Receptors in Interleukin-2 Synthesis in Lymphocytes

Receptors for many neurotransmitters including catecholamines and acetylcholine (ACh) have been detected on the cell surface of lymphocytes. It has been demonstrated that a human T cell line synthesizes ACh and suggested that ACh may be an autacoid modulating T cell-dependent immune responses. However, the biochemical interactions of the ACh system with the immune system have not been elucidated in detail. We have shown that m1 and m2 muscarinic receptor mRNAs are expressed in human peripheral blood lymphocytes and in human T cell line Jurkat cells and that pretreatment of these cells with a muscarinic receptor agonist enhances interleukin-2 (IL-2) production. We also postulated possible intracellular signaling pathways via which muscarinic receptors regulate IL-2 production in Jurkat cells. The findings suggest that M1 muscarinic receptors are involved in muscarinic receptor-mediated enhancement of IL-2 production in Jurkat cells and that the transcription factor AP-1 and pathways via mitogen-activated protein kinase (MAPK)/extracellular signal regulated protein kinase and c-Jun N-terminal kinase, but not via p38 MAPK, may be involved in the muscarinic receptor-mediated enhancement of IL-2 production. Our findings demonstrate a neuro-immune interaction through muscarinic receptor signaling in immune cells.

S17-3 - Role of muscarinic acetylcholine receptors on interleukin-2 formation in lymphocytes

S17-3 - Role of muscarinic acetylcholine receptors on interleukin-2 formation in lymphocytes

Muscarinic receptors mediate enhancement of spontaneous GABA release in the chick brain

The functional role of muscarinic acetylcholine receptors in the lateral spiriform nucleus was studied in chick brain slices. Whole-cell patch-clamp recordings of neurons in the lateral spiriform nucleus revealed that carbachol enhanced GABAergic spontaneous inhibitory postsynaptic currents. The duration of the response to carbachol was significantly reduced after blockade of muscarinic receptors with atropine. In the presence of the nicotinic receptor antagonist dihydro-β-erythroidine, carbachol produced a delayed but prolonged enhancement of spontaneous GABAergic inhibitory postsynaptic currents that was completely blocked by atropine. Muscarine also enhanced the frequency of spontaneous GABAergic inhibitory postsynaptic currents in a dose-dependent manner, but had no effect on inhibitory postsynaptic current amplitude. While 4-diphenylacetoxy- N-(2-chloroethyl)-piperidine hydrochloride, a M 3 antagonist, completely blocked muscarine's effect, telenzepine, a M 1 antagonist, and tropicamide, a M 4 antagonist, only partially decreased the response to muscarine. Pirenzepine, a M 1 antagonist, and methoctramine, a M 2 antagonist, potentiated muscarine's enhancement of spontaneous GABAergic inhibitory postsynaptic currents. Muscarine's action was blocked by tetrodotoxin, cadmium chloride and ω-conotoxin GVIA, but was not affected by dihydro-β-erythroidine, 6-cyano-7-nitroquinoxaline-2,3-dione, d(−)-2-amino-5-phosphonopentanoic acid, naloxone or fluphenazine. These results demonstrate that activation of both muscarinic and nicotinic acetylcholine receptors can enhance GABAergic inhibitory postsynaptic currents in the lateral spiriform nucleus. The muscarinic response has a slower onset but lasts longer than the nicotinic effect. The M 3 receptor subtype is predominantly involved in enhancing spontaneous GABAergic inhibitory postsynaptic currents. These M 3 receptors must be located some distance from GABA release sites, since activation of voltage-dependent sodium channels, and consequent activation of N-type voltage-dependent calcium channels, is required to trigger enhanced GABA release following activation of muscarinic receptors.

Stimulatory roles of muscarinic acetylcholine receptors on T cell antigen receptor/CD3 complex-mediated interleukin-2 production in human peripheral blood lymphocytes.

It is known that there are some bidirectional interactions between the nervous and the immune systems via neurotransmitters and cytokines. To clarify whether any neurotransmitters modulate lymphocyte functions, we examined the effects of oxotremorine-M (Oxo-M) on interleukin-2 (IL-2) production in human peripheral blood lymphocytes by using enzyme-linked immunosorbent assays, Northern blot analyses, reverse transcriptase-polymerase chain reaction, and fluorescence-activated cell sorter. Pretreatment of cells with Oxo-M (10 nM to 10 microM) for 4-24 hr enhanced phytohemagglutinin (PHA)-induced IL-2 mRNA expression and markedly increased IL-2 production compared with those induced by PHA alone. Oxo-M alone did not affect IL-2 mRNA expression and IL-2 production. In CD3-positive T cells, pretreatment with Oxo-M for 24 hr enhanced PHA-induced IL-2 production. Furthermore, pretreatment with Oxo-M enhanced PHA-induced mRNA expression of the alpha and beta subunits of IL-2 receptors and DNA synthesis. Cytometric analysis showed Oxo-M treatment did not up-regulate expression of cell surface molecules such as CD3, CD2, CD4, CD8, and IL-2 receptors. These results suggest that activation of muscarinic receptors enhances T cell antigen receptor/CD3-induced IL-2 production.

O-183 - Roles of muscarinic acetylcholine receptors in interleukin-2 production in the human T cell line, Jurkat cells

O-183 - Roles of muscarinic acetylcholine receptors in interleukin-2 production in the human T cell line, Jurkat cells

P-653 - Different role of muscarinic acetylcholine receptors (mAChR) in the urethral smooth muscle of male rabbit

P-653 - Different role of muscarinic acetylcholine receptors (mAChR) in the urethral smooth muscle of male rabbit

Autoradiographic localization of muscarinic receptors within the rat kidney

We used a combination of radioreceptor binding and autoradiographic techniques to study the pharmacological characteristics and anatomical localization of [ 3H]quinuclidinyl benzylate (QNB) in kidney sections of Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). [ 3H]QNB was bound by sections of rat kidney in a manner consistent with the labeling of muscarinic acetylcholine receptors. Anatomically, these receptor sites were located primarily within the smooth muscle of the renal vascular tree and to a lesser extent within cortical and medullary tubules. The density of renal muscarinic acetylcholine receptors (both vascular and tubular) was decreased in hypertension but the affinity of the ligand for muscarinic receptors was unchanged. A possible role of muscarinic acetylcholine receptors in renal function is suggested.