Alzheimer's disease is a central nervous system disorder characterized by the presence of neurofibrillary tangles, neuritic plaques and dystrophic neurites in susceptible areas of the brain. Investigation of the mechanism and development of the disease has been hampered by the lack of an animal model and the inaccessibility of neural tissue during the illness. Deficits in odour detection and discrimination are among the signs of Alzheimer's and previous anatomical studies suggest that olfactory pathways may be involved early in the illness. Neurons in the olfactory epithelium, which are of central origin, are relatively accessible for biopsy and could be used as a source of living nerve cells for the study of Alzheimer's disease if they can be shown to have characteristics of this disease. As these neurons have the unusual property of arising from stem cells throughout the life of the organism, they are good candidates for the development of cell cultures or cell lines which may express the disorder from living patients. We report here that nasal epithelium tissue taken at autopsy shows unique pathological changes in morphology, distribution and immunoreactivity of neuronal structures in patients with Alzheimer's disease.
The effects of ATP on salivary glands have been recognized since 1982. Functional and pharmacological studies of the P2 nucleotide receptors that mediate the effects of ATP and other extracellular nucleotides have been supported by the cloning of receptor cDNAs, by the expression of the receptor proteins, and by the identification in salivary gland cells of multiple P2 receptor subtypes. Currently, there is evidence obtained from pharmacological and molecular biology approaches for the expression in salivary gland of two P2X ligand-gated ion channels, P2Z/P2X7 and P2X4, and two P2Y G protein-coupled receptors, P2Y1 and P2Y2. Activation of each of these receptor subtypes increases intracellular Ca2+, a second messenger with a key role in the regulation of salivary gland secretion. Through Ca2+ regulation and other mechanisms, P2 receptors appear to regulate salivary cell volume, ion and protein secretion, and increased permeability to small molecules that may be involved in cytotoxicity. Some localization of the various salivary P2 receptor subtypes to specific cells and membrane subdomains has been reported, along with evidence for the co-expression of multiple P2 receptor subtypes within specific salivary acinar or duct cells. However, additional studies in vivo and with intact organ preparations are required to define clearly the roles the various P2 receptor subtypes play in salivary gland physiology and pathology. Opportunities for eventual utilization of these receptors as pharmacotherapeutic targets in diseases involving salivary gland dysfunction appear promising.
Effects of several purinergic receptor agonists were examined on rat parotid acinar cells. Extracellular ATP stimulated 45Ca2+ uptake into isolated rat parotid acinar cells in a concentration-dependent fashion (EC50 approximately 125 microM ATP) at a maximum rate of approximately 6 nmol.mg protein-1.min-1. In the absence of extracellular Na+, ATP increased the uptake rate by greater than 100%. Increasing concentrations of extracellular Na+ reduced the ATP-stimulated rate of 45Ca2+ entry in a graded fashion (IC50 16.6 mM), suggesting that Ca2+ and Na+ compete for entry. Uptake rate was not reduced when intracellular Ca2+ was buffered with 1,2-bis(2-aminophenoxy)ethane-N,N,N'N'-tetraacetic acid, indicating that the effects of ATP were not initiated by an elevation in intracellular free Ca2+ concentration. 3-O-(4'-benzoyl)benzoyl-ATP was much more potent (EC50 approximately 4 microM) and stimulated Ca2+ influx at a greater rate (approximately 12 nmol.mg protein-1.min-1) than ATP. Other nucleotide analogues, including adenosine 5'-O-(3-thiotriphosphate), 2-methylthio-ATP, and 5'-adenylylimidodiphosphate, were much less effective than ATP. ATP produced a biphasic effect on membrane potential: an initial hyperpolarization was followed by a rapid depolarization. The depolarization was greatly reduced in the absence of extracellular Na+, but not in the absence of extracellular Ca2+, indicating that the majority of the depolarizing current was due to Na+ entry. Effects of ATP on the membrane potential were distinguishable from those of the Ca2+ ionophore ionomycin and the muscarinic agonist carbachol. Depolarization of the cells by gramicidin or K+ did not produce an increase in 45Ca2+ uptake.(ABSTRACT TRUNCATED AT 250 WORDS)
The effects of extracellular ATP on ion fluxes and the intracellular free Ca 2 § concentration ([Ca~+]i) were examined using a suspension of rat parotid acinar cells and were contrasted with the effects of the muscarinic agonist carbachol. Although ATP and carbachol both rapidly increased [Ca2+] i about threefold above the resting level (200-250 nM), the effect of ATP was due primarily to an influx of Ca ~+ across the plasma membrane, while the initial response to carbachol was due to a release of Ca ~ § from intracellular stores. Within 10 s, ATP (1 mM) and carbachol (20 #M) reduced the cellular C1-content by 39-50% and cell volume by 15-25%. Both stimuli reduced the cytosolic K + content by 57-65%, but there were marked differences in the rate and pattern of net K § movement as well as the effects of K + channel inhibitors on the effluxes initiated by the two stimuli. The maximum rate of the ATP-stimulated K § efflux (~2,200 nmol K+/mg protein per min) was about two-thirds that of the carbachol-initiated efflux rate, and was reduced by ~30% (vs. 60% for the carbachol-stimulated K + efflux) by TEA (tetraethylammonium), an inhibitor of the large conductance (BK) K § channel. Charybdotoxin, another K § channel blocker, was markedly more effective than TEA on the effects of both agonists, and reduced the rate of K § effiux initiated by both ATP and carbachol by ~80%. The removal of extracellular Ca ~ § reduced the ATPand the carbachol-stimulated rates of K + efflux by 55 and 17%, respectively. The rate of K + effiux initiated by either agonist was reduced by 78-95% in cells that were loaded with BAPTA to slow the elevation of [Ca2+]i. These results indicated that ATP and carbachol stimulated the effiux of K + through multiple types of K § permeable channels, and demonstrated that the relative proportion of efflux 320THE JOURNAL OF GENERAL PHYSIOLOGY 9 VOLUME 95 9 1990 through the different pathways was different for the two stimuli. ATP and carbachol also stimulated the rapid entry of Na § into the parotid cell, and elevated the intracellular Na § content to 4.4 and 2.6 times the normal level, respectively. The rate of Na § entry through Na+-K+-2CI-cotransport and Na+-H § exchange was similar whether stimulated by ATP, carbachol, or ionomycin, and uptake through these two carrier-mediated transporters accounted for 50% of the ATP-promoted Na § influx. The remainder may be due to a nonselective cation channel and an ATP-gated cation channel that is also permeable to Ca ~ § The consumption of extracellular ATP by an ecto-ATPase (apparent K0.5 for ATP is 0.93 mM) on the plasma membrane limited the duration of the response to ATP when large concentrations of cells were used. The effects of ATP on [Ca~+]i and ion fluxes were blocked specifically by DIDS (4,4'-diisothiocyanostilbene-2,2'-disulfonic acid), and were more potent in the absence of Mg ~+, suggesting that the active nucleotide moiety was ATP 4-. These studies suggest that ATP may function as a neurotransmitter and modulate fluid secretion by stimula...
1 Increasing concentrations of ATP (0.511M-300 gM) produced a biphasic increase in intracellular calcium concentration [Ca] 6 Parasympathetic denervation selectively increased the more sensitive response, suggesting that it may be physiologically regulated.
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