The epithelial cholinergic system of the airways

Acetylcholine (ACh), a classical transmitter of parasympathetic nerve fibres in the airways, is also synthesized by a large number of non-neuronal cells, including airway surface epithelial cells. Strongest expression of cholinergic traits is observed in neuroendocrine and brush cells but other epithelial cell types—ciliated, basal and secretory—are cholinergic as well. There is cell type-specific expression of the molecular pathways of ACh release, including both the vesicular storage and exocytotic release known from neurons, and transmembrane release from the cytosol via organic cation transporters. The subcellular distribution of the ACh release machineries suggests luminal release from ciliated and secretory cells, and basolateral release from neuroendocrine cells. The scenario as known so far strongly suggests a local auto-/paracrine role of epithelial ACh in regulating various aspects on the innate mucosal defence mechanisms, including mucociliary clearance, regulation of macrophage function and modulation of sensory nerve fibre activity. The proliferative effects of ACh gain importance in recently identified ACh receptor disorders conferring susceptibility to lung cancer. The cell type-specific molecular diversity of the epithelial ACh synthesis and release machinery implies that it is differently regulated than neuronal ACh release and can be specifically targeted by appropriate drugs

Choline transporter gene variation is associated with attention-deficit hyperactivity disorder

The neurotransmitter acetylcholine (ACh) plays a critical role in brain circuits mediating motor control, attention, learning and memory. Cholinergic dysfunction is associated with multiple brain disorders including Alzheimer’s Disease, addiction, schizophrenia and Attention-Deficit Hyperactivity Disorder (ADHD). The presynaptic choline transporter (CHT, SLC5A7) is the major, rate-limiting determinant of ACh production in the brain and periphery and is consequently upregulated during tasks that require sustained attention. Given the contribution of central cholinergic circuits to the control of movement and attention, we hypothesized that functional CHT gene variants might impact risk for ADHD. We performed a case-control study, followed by family-based association tests on a separate cohort, of two purportedly functional CHT polymorphisms (coding variant Ile89Val (rs1013940) and a genomic SNP 3’ of the CHT gene (rs333229), affording both a replication sample and opportunities to reduce potential population stratification biases. Initial genotyping of pediatric ADHD subjects for two purportedly functional CHT alleles revealed a 2–3 fold elevation of the Val89 allele (n = 100; P = 0.02) relative to healthy controls, as well as a significant decrease of the 3’SNP minor allele in Caucasian male subjects (n = 60; P = 0.004). In family based association tests, we found significant overtransmission of the Val89 variant to children with a Combined subtype diagnosis (OR = 3.16; P = 0.01), with an increased Odds Ratio for a haplotype comprising both minor alleles. These studies show evidence of cholinergic deficits in ADHD, particularly for subjects with the Combined subtype, and, if replicated, may encourage further consideration of cholinergic agonist therapy in the disorder

Biochemical, autoradiographic and pharmacological evidence for the involvement of tubular DA-1 receptors in the natriuretic response to dopexamine hydrochloride.

Dopexamine hydrochloride (DPX) is a dopamine analog and it possesses agonistic action at DA-1 receptors and beta 2-adrenoceptors. It also is a weak agonist at DA-2 receptors. In the present study, we have examined the anatomical localization of DPX binding sites in rat kidney and their functional significance in terms of the renal effects of this compound. In receptor-ligand binding studies, [3H]-DPX was found to bind specifically to sections of rat kidney in a time (maximum binding at 60 min), temperature (optimal temperature 25 degrees C) and concentration (highest specific/non-specific ratio at 2 nmol/l) dependent manner. Autoradiographic studies revealed the presence of [3H]-DPX binding sites in renal tubules, glomerulus and various layers of small and large blood vessels. Inhibition studies with SCH 23390, ICI 118.551 and 1-sulpiride showed that DPX binds primarily to DA-1 receptors in tubules, only to beta 2-adrenoceptors in glomerulus and to beta 2-adrenoceptors, DA-1 and DA-2 receptors in blood vessels. Also, DPX caused concentration related increases in cyclic AMP levels in rat kidney membrane particles, which could be completely abolished by a combined presence of SCH 23390 and propranolol suggesting that both binding sites of DPX are linked to adenylate cyclase. In functional studies DPX (1 microgram/kg.min for 30 min) produced a modest fall in blood pressure, pronounced tachycardia and slight but significant increase in renal blood flow (11%). These responses were accompanied by increases in urine output (97%), urinary sodium excretion (89%), and fractional excretion of sodium (132%). There was no change in glomerular filtration rate. Propranolol pretreatment abolished DPX-induced hypotension and tachycardia but seemed to potentiate the natriuretic responses to DPX. On the other hand, SCH 23390, a DA-1 receptor antagonist completely abolished DPX-induced hypotension, natriuresis and diuresis without affecting tachycardia. These results indicate that (1) DPX binds predominantly to DA-1 receptors in renal tubules, to beta 2-adrenoceptors in glomerulus and to beta 2-adrenoceptors, as well as DA-1 and DA-2 receptors in renal blood vessels (2) DPX stimulates cAMP formation in the kidney by activating both DA-1 and beta 2-adrenoceptors and (3) DPX produces natriuresis and diuresis by selectively activating DA-1 receptors located on renal tubules

Antidepressants targeting the serotonin reuptake transporter act via a competitive mechanism. J Pharmacol Exp Ther

ABSTRACT Although several antidepressants (including fluoxetine, imipramine, citalopram, venlafaxine, and duloxetine) are known to inhibit the serotonin transporter (SERT), whether or not these molecules compete with 5-hydroxytryptamine (serotonin) (5-HT) for binding to SERT has remained controversial. We have performed radioligand competition binding experiments and found that all data can be fitted via a simple competitive interaction model, using Cheng-Prusoff analysis (Biochem Pharmacol 22: 3099 -3108, 1973 In accordance with the Cheng-Prusoff relationship for a competitive interaction, we observed that test compound concentrations associated with 50% maximal inhibition of radiotracer binding (IC 50 ) increased linearly with increasing radioligand concentration for all ligands: 5-HT, S-citalopram, R-citalopram, paroxetine, clomipramine, fluvoxamine, imipramine venlafaxine, duloxetine, indatraline, cocaine, and 2-␤-carboxy-3-␤-(4-iodophenyl)tropane. The equilibrium dissociation constant of 5-HT and SERT inhibitors were also derived using Scatchard analysis of the data set, and they were found to be comparable with the data obtained using the ChengPrusoff relationship. Our studies establish a reference framework that will contribute to ongoing efforts to understand ligand binding modes at SERT by demonstrating that 5-HT and the SERT inhibitors tested bind to the serotonin transporter in a competitive manner