Extracellular ATP prevents the release of stored Ca2+ by autonomic agonists in rat submandibular gland acini

Measurement of [Cl] i , BzATP in both SMG cell types largely activated the Ca 2؉ -independent, glibenclamide-sensitive Cl ؊ current, whereas UTP activated only the Ca 2؉ -dependent Cl ؊ current. We interpret this to suggest that BzATP and UTP largely activate Cl ؊ channels residing in the membrane expressing the receptor for the active nucleotide. The present studies reveal a potentially new mechanism for transcellular Cl ؊ transport in a CFTR-expressing tissue, the SMG. Coordinated action of the P 2 z (luminal) and P 2 u (basolateral) receptors can mediate part of the transcellular Cl ؊ transport by acinar and duct cells to determine the final electrolyte composition of salivary fluid.

Section: Discussionmentioning

confidence: 99%

“…Agonists acting through cAMP elevation can activate CFTR in acinar and duct cells (9,16). Salivary acinar and duct cells also respond to purinergic stimulation by a change in [Ca 2ϩ ] i (17)(18)(19)(20)(21)(22). However, the identities of the receptors and whether they regulate Cl Ϫ channels in salivary gland cells are not known.…”

mentioning

confidence: 99%

Membrane-specific Regulation of Cl− Channels by Purinergic Receptors in Rat Submandibular Gland Acinar and Duct Cells

Zeng

Lee

Muallem

1997

“…Synaptic modulation via depolarization and calcium entry may modify parotid secretion. At other synapses, ATP acts as a modulatory cotransmitter, and ATP has been reported to inhibit muscarinic and tachykinin responses through the P 2z receptor in submandibular or parotid cells (38,64,65), although relatively high concentrations of ATP are required for activation in the presence of divalent cations.…”

Section: Sensitivity Receptor Sensitivity To Atp In Individual Cellsmentioning

confidence: 99%

Expression and Trans-synaptic Regulation of P2x4 and P2z Receptors for Extracellular ATP in Parotid Acinar Cells

Tenneti

Gibbons

Talamo

1998

Trans-synaptic regulation of muscarinic, peptidergic, and purinergic responses after denervation has been reported previously in rat parotid acinar cells (McMillian, M. K., Soltoff, S. P., Cantley, L. C., Rudel, R., and Talamo, B. R. (1993) Br. J. Pharmacol. 108, 453-461). Characteristics of the ATP-mediated responses and the effects of parasympathetic denervation were further analyzed through assay of Ca 2؉ influx, using fluorescence ratio imaging methods, and by analysis of P 2x receptor expression. ATP activates both a high affinity and a low affinity response with properties corresponding to the recently described P 2x4 and the P 2z (P 2x7 )-type purinoceptors, respectively. Reverse transcription-polymerase chain reaction analysis reveals mRNA for P 2x4 as well as P 2x7 subtypes but not P 2x1 , P 2x2 , P 2x3 , P 2x5 , or P 2x6 . P 2x4 protein also is detected by Western blotting. Distribution of the two types of ATP receptor responses on individual cells was stochastic, with both high and low affinity responses on some cells, and only a single type of response on others. Sensitivity to P 2x4 -type activation also varied even among cells responsive to low concentrations of ATP. Parasympathetic denervation greatly enhanced responses, tripling the proportion of acinar cells with a P 2x4 -type response and increasing the fraction of highly sensitive cells by 7-fold. Moreover, P 2x4 mRNA is significantly increased following parasympathetic denervation. These data indicate that sensitivity to ATP is modulated by neurotransmission at parasympathetic synapses, at least in part through increased expression of P 2x4 mRNA, and suggest that similar regulation may occur at other sites in the nervous system where P 2x4 receptors are widely expressed.Extracellular ATP acts as a signaling molecule through the interaction of ATP with ligand-gated ion channels (P 2x ) as well as metabotropic receptors (P 2y ) (for reviews see Refs. 2-4). These receptors are distributed throughout the body, including synapses where ATP seems to function as a neurotransmitter (5, 6). The pharmacology and physiology of ATP-activated ion fluxes indicate the existence of multiple subtypes of P 2x receptors, confirmed by molecular cloning of seven genes for P 2x receptor subunits (3,(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17).Relatively little is known about the physiological regulation of P 2x receptors. We have shown that removal of the autonomic innervation alters ATP responses in parotid acinar cells, which therefore provide a good model for investigating trans-synaptic regulation of receptor-mediated signaling. We previously described two ATP responses in rat parotid acinar cells, a P 2z/x7 type and a high affinity ATP receptor with distinctly different P 2x -like pharmacology (1).Expression of the P 2x -type proteins in heterologous systems shows that each can form functional, homomeric, ligand-gated ion channels with a significant permeability to Ca 2ϩ ions as well as other inorganic cations, including Na ϩ and K ϩ . Properties of P 2x7 recept...

“…Salivary acinar and duct cells also respond to purinergic stimulation by a change in [Ca 2ϩ ] i (15,(17)(18)(19)(20)(21)(22). However, the identity of the receptors and their membrane localization is not clear.…”

Section: ؉mentioning

confidence: 99%

“…In the duct the same agonists reduce the transepithelial potential and Na ϩ reabsorption (6 -8). Work on the cellular level showed that cholinergic and ␣-adrenergic agonists act on salivary acinar and duct cells to increase [Ca 2ϩ ] i (10 -15), and ␤-adrenergic agonists increase cAMP (11,16).Salivary acinar and duct cells also respond to purinergic stimulation by a change in [Ca 2ϩ ] i (15,(17)(18)(19)(20)(21)(22). However, the identity of the receptors and their membrane localization is not clear.…”

mentioning

confidence: 99%

Characterization and Localization of P2 Receptors in Rat Submandibular Gland Acinar and Duct Cells

Lee

Zeng

Muallem

1997

[Ca 2؉] i and the Cl ؊ current were measured in isolated submandibular gland acinar and duct cells to characterize and localize the purinergic receptors expressed in these cells. In both cell types 2-3-benzoylbenzoyl (Bz)-ATP and ATP increased [Ca 2؉ ] i mainly by activation of Ca 2؉ influx. UTP had only minimal effect on [Ca 2؉ ] i at concentrations between 0.1 and 1 mM. However, a whole cell current recording showed that all nucleotides effectively activated Cl ؊ currents. Inhibition of signal transduction through G proteins by guanyl-5-␤-thiophosphate revealed that the effect of ATP on Cl ؊ current was mediated in part by activation of a G protein-coupled and in part by a G protein-independent receptor. BzATP activated exclusively the G protein-independent portion, whereas UTP activated only the G protein- Ϫ . Acinar cells secrete the primary, NaCl-rich fluid into the duct, which reabsorbs most of the NaCl in exchange for K ϩ -HCO 3 Ϫ (1). As in any other CFTR-expressing tissues (2-4) and Na ϩ -transporting epithelia (5), Cl Ϫ channels play a central role in transcellular ion transport in the two cell types of SMG (1). However, unlike that of other epithelia, little is known of the regulation of Cl Ϫ channels in salivary gland cells, in particular regulation by purinergic (P 2 ) receptors.In the intact salivary gland secretion is regulated by several agonists, which include cholinergic, ␣-adrenergic, and ␤-adrenergic agonists (6 -8). The agonists act on both acinar and duct cells but modulate different activities in the two cell types. In acinar cells the agonists stimulate secretion primarily by stimulation of the basolateral NaKCl 2 cotransporter (9). In the duct the same agonists reduce the transepithelial potential and Na ϩ reabsorption (6 -8). Work on the cellular level showed that cholinergic and ␣-adrenergic agonists act on salivary acinar and duct cells to increase [Ca 2ϩ ] i (10 -15), and ␤-adrenergic agonists increase cAMP (11,16).Salivary acinar and duct cells also respond to purinergic stimulation by a change in [Ca 2ϩ ] i (15,(17)(18)(19)(20)(21)(22). However, the identity of the receptors and their membrane localization is not clear. Response of duct cells to BzATP and several other nucleotides suggested that duct cells express P 2 z and P 2 Y 1 receptors (37). Response of acinar cells to BzATP was interpreted to suggest that acinar cells express P 2 z receptors (20, 22). More recently it was shown that acinar and duct cells in long term culture up-regulate the P 2 Y 2 receptors (23). However, whether native and freshly isolated cells express P 2 Y 2 receptors and how these and other purinergic receptors regulate cellular activity is not known. P 2 receptors are believed to play a central role in regulating Cl Ϫ transport in CFTR-expressing tissues (3, 4, 24 -27). Because of our recent findings of CFTR expression in SMG duct and acinar cells (28) and the expression of P 2 receptors in SMG cells (15,(17)(18)(19)(20)(21)(22), in the present work we studied the regulation of Cl Ϫ channel...