Transient up-regulation of P2Y2 nucleotide receptor mRNA expression is an immediate early gene response in activated thymocytes

In studies designed to understand the roles of P2 nucleotide receptors in differentiation of T lymphocytes, we observed a transient and protein synthesis-independent enhancement of mRNA expression for the G protein-coupled P2Y2 receptor in mouse thymocytes after the addition of steroid hormone or T cell receptor (TCR) crosslinking by anti-TCR mAb. Conversely, dexamethasone-induced increases in mRNA expression for the ligand-gated ion channel P2X1 receptor was detected in rat, but not mouse, thymocytes, raising questions about the previously suggested role of P2X1 receptors in thymocyte apoptosis. Flow cytometry analysis of thymocyte subsets excluded the possibility that the observed increases in P2Y2 receptor mRNA expression were due to the enrichment of steroid-treated cells with an P2Y2 mRNA-rich thymocyte subset. Triggering of TCR-mediated intracellular signaling pathways through crosslinking of TCR or by addition of phorbol ester and Ca2+ ionophore also resulted in the up-regulation of P2Y2, but not P2X1, receptor mRNA. It is proposed that the rapid increase of P2Y2 receptor mRNA expression could be a common early event in responses of T cells to different activating stimuli. Taken together with the recently discovered ability of nucleotide receptor-initiated signaling to antagonize or enhance the effects of TCR crosslinking or steroids on thymocytes, the observed rapid up-regulation of P2Y2 receptor mRNA expression may reflect an immediate early gene response where newly expressed cell surface nucleotide receptors provide regulatory feedback signaling from extracellular ATP in the T cell differentiation process.

Cloned and transfected P2Y4 receptors: characterization of a suramin and PPADS-insensitive response to UTP

The P2Y family of receptors are G protein-coupled receptors for ATP, ADP, UTP and UDP. Recently several members of this family have been cloned, including the P2Y4, which is activated by UTP but not by ATP. In the present report, using receptors stably transfected into 1321N1 cells, we show that suramin acts as an antagonist at cloned P2Y1 and (less potently) P2Y2 receptors, but not at the cloned P2Y4 receptor. Furthermore, PPADS (pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid), a potent antagonist at the P2Y1 receptor, is a relatively inneffective antagonist at the cloned P2Y4 receptor. This work moves us closer to the goal of classifying the native P2Y receptors on the basis of agonist and antagonist profiles.

PPADS and suramin as antagonists at cloned P2Y- and P2U-purinoceptors

1. The effect of suramin and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) on the stimulation of phospholipase C in 1321N1 cells transfected with the human P2U-purinoceptor (h-P2U-1321N1 cells) or with the turkey P2Y-purinoceptor (t-P2Y-1321N1 cells) was investigated. 2-Methylthioadenosine triphosphate (2MeSATP) was used as the agonist at t-P2Y-1321N1 cells and uridine triphosphate (UTP) at h-P2U-1321N1 cells. 2. Suramin caused a parallel shift to the right of the concentration-response curves for 2MeSATP in the t-P2Y-1321N1 cells, yielding a Schild plot with a slope of 1.16 +/- 0.08 and a pA2 value of 5.77 +/- 0.11. 3. Suramin also caused a shift to the right of concentration-response curves for UTP in the h-P2U-1321N1 cells, and on Schild plots gave a slope different from unity (1.57 +/- 0.19) and an apparent pA2 value of 4.32 +/- 0.13. Suramin was therefore a less potent antagonist at the P2U-purinoceptor than the P2Y-purinoceptor. 4. In the presence of the ectonucleotidase inhibitor, ARL 67156 (6-N,N-diethyl-beta,gamma-dibromomethylene-D-ATP) there was no significant difference in the EC50 or shapes of curves with either cell type, and no difference in pA2 values for suramin. 5. PPADS caused an increase in the EC50 for 2MeSATP in the t-P2Y-1321N1 cells. The Schild plot had a slope different from unity (0.55 +/- 0.15) and an X-intercept corresponding to an apparent pA2 of 5.98 +/- 0.65. 6. PPADS up to 30 microM had no effect on the concentration-response curve for UTP with the h-P2U-1321N1 cells. 7. In conclusion, suramin and PPADS show clear differences in their action at the 2 receptor types, in each case being substantially more effective as an antagonist at the P2Y-purinoceptor than at the P2U-purinoceptor. Ectonucleotidase breakdown had little influence on the nature of the responses at the two receptor types, or in their differential sensitivity to suramin.

Effects of endophyte-infected tall fescue, environmental temperature and prazosin injection on the rat

Effects of an alpha 1 antagonist, prazosin, injection on the rat (Rattus rattus) exposed to warm vs normal environments and fed endophyte-infected (E+) or -free (E-) tall fescue seed were studied. Rats were injected IP daily with placebo or prazosin (1 mg/kg BW). Daily skin and rectal temperatures and food intake measurements were recorded. Selected brain tissues were dissected to determine treatment effects on monoamine receptor density. Rats fed E+ and injected with placebo had reduced (P < 0.01) food intake compared with all other treatments. By day 5 of injection, an endophyte x temperature interaction for increased (P < 0.03) skin and rectal temperatures was measured when rats were fed E+ and housed at 32 degrees C. Also by day 5, injection of rats consuming E+ with prazosin reduced (P < 0.01) skin and rectal temperatures 0.4 degree C compared with those consuming E+ and injected with placebo. Monoamine receptor (alpha 1, alpha 2, and D2) densities were similar (P > 0.10) among treatments. Prazosin injection reduced E+ induced body temperature increases chronically and increased food intake acutely to E- levels. Monoamine receptor densities were unchanged; therefore, E+ effects via monoamine receptors may be due to acute modulation of receptor-associated activity.

A regulatory role in mammalian salivary glands for 5-hydroxytryptamine receptors coupled to increased cyclic AMP production

Although a functional role for serotonin (5-hydroxytryptamine, 5-HT) has been defined in the salivary glands of some lower species, relatively few data supporting a role for 5-HT in the regulation of mammalian salivary glands have been presented. Our initial results from polymerase chain reaction studies in cells of mammalian submandibular gland origin using consensus sequence primers from G protein-coupled receptors suggested the presence of mRNA for a 5-HT receptor in these cells. Based on this observation, the question of a role for 5-HT in mammalian submandibular gland function was re-addressed, using isolated, perfused rat submandibular glands and dispersed-cell aggregates from this gland. In perfused glands, 5-HT decreased the rate of saliva flow initiated by acetylcholine by about 50% and increased the amount of protein in the saliva two-fold. In dispersed-cell aggregates, 5-HT elicited a concentration-dependent increase in the accumulation of adenosine 3',5' monophosphate (cyclic AMP; EC50 = 660 +/- 110 nM). In addition, functional studies, as well as radioligand binding experiments, indicated that the effects of 5-HT are independent of beta-adrenoceptors. Accumulation of cAMP in gland cells was consistent with a direct action of 5-HT on adenylyl cyclase. Similar cyclic AMP responses to 5-HT were observed in cells isolated from mouse and opossum submandibular glands and rat sublingual and parotid glands. Our findings suggest the presence of a 5-HT receptor in mammalian salivary glands coupled to the stimulation of adenylyl cyclase and, at least in rat submandibular gland, involved in modifying the volume and protein content of saliva.

Potentiation of regulatory volume decrease by P2U purinoceptors in HSG-PA cells

HSG-PA human salivary gland duct cells exhibit progressively increased regulatory volume decrease (RVD) in response to decreased medium osmolarity. The P2U purinoceptor agonist UTP causes a potentiation of RVD, the extent of which is most pronounced in 220 mosM medium and is least apparent in 180 mosM medium. We examined the underlying mechanisms for this effect. Exposure of HSG-PA cells to UTP promotes Ca2+ mobilization, hyperpolarization, and net K+ efflux, suggesting the participation of Ca(2+)-activated K+ channels in RVD. To delineate the anion counterpart of K+ movement during RVD, cell swelling in the presence of gramicidin, which abolishes the membrane potential, was measured. In response to a sudden dilution in hypotonic media, gramicidin-treated cells swelled immediately, followed by a "secondary swelling" in 180 but not in 220 mosM medium. The results suggest that in 180 mosM cells perform spontaneous RVD mediated by increased anion conductance. In 220 mosM medium in which RVD is minimal, the increase in anion conductance is marginal. In our model of RVD in which cells were challenged by UTP, the ensuing hyperpolarization provides the driving force for net Cl- efflux, which is confirmed by tracer flux studies during purinoceptor-activated RVD. Thus RVD, which has long been regarded as a self-sufficient cellular program, appears to be subject to extracellular control in HSG-PA cells through receptor-mediated processes.

Cloning, expression, and chromosomal localization of the human uridine nucleotide receptor gene

Extracellular ATP and ADP mediate diverse physiological responses in mammalian cells, in part through the activation of G protein-coupled P2 purinoceptors. The cloning and expression of cDNAs encoding several P2 purinoceptor subtypes have enabled rapid advances in our understanding of the structural and functional properties of these receptors. The current report describes the isolation of a gene from a human genomic library that encodes a protein with the greatest similarity to the human P2U purinoceptor, a subtype that is distinguished by its ability to be activated by uridine nucleotides as well as adenine nucleotides. When expressed in a mammalian cell line, this novel receptor is activated specifically by UTP and UDP but not by ATP and ADP. Activation of this uridine nucleotide receptor resulted in increased inositol phosphate formation and calcium mobilization. Fluorescence in situ hybridization revealed that the gene encoding the uridine nucleotide receptor is located in region q13 of the X chromosome. Dendrogram analysis of the G protein-coupled P2 purinoceptors and the uridine nucleotide receptor indicates that these receptors belong to a family that may be more aptly named nucleotide receptors.

Critical issues in reforming rural mental health service delivery

Critical issues in reforming rural mental health service delivery systems under health care reform are outlined. It is argued that the exclusive focus on health care financing reform fails to include obstacles to effective mental health service delivery in rural area, which should focus on issues of availability, accessibility, and acceptability, as well as financing and accountability. Characteristics of rural areas are delineated and three assumptions about the structure of rural communities which are shaping the dialogue on rural health and mental health service delivery are examined. These assumptions include the notion that rural communities are more closely knit than urban ones, that rural services can be effectively delivered through urban hubs, and that rural dwellers represent a low risk population which can be effectively served through existing facilities and by extending existing services.

Ergovaline binding and activation of D2 dopamine receptors in GH4ZR7 cells

Ergovaline inhibition of radioligand binding to the D2 dopamine receptor and ergot alkaloid inhibition of vasoactive intestinal peptide (VIP)-stimulated cyclic AMP production in GH4ZR7 cells, stably transfected with a rat D2 dopamine receptor, were evaluated. Ergovaline inhibition of the binding of the D2-specific radioligand, [3H]YM-09151-2, exhibited a KI (inhibition constant) of 6.9 +/- 2.6 nM, whereas dopamine was much less potent (370 +/- 160 nM). Ergot alkaloids were also effective in inhibiting VIP-stimulated cyclic AMP production, with EC50 values for ergovaline, ergonovine, alpha-ergocryptine, ergotamine, and dopamine of 8 +/- 2, 47 +/- 2, 28 +/- 2, 2 +/- 1, and 8 +/- 1 nM, respectively. Inhibition of cyclic AMP production by ergovaline was blocked by the dopamine receptor antagonist, (-)-sulpiride (IC50, 300 +/- 150 nM). Our results indicate that ergot compounds, especially ergovaline, bind to D2 dopamine receptors and elicit second messenger responses similar to that of dopamine. These findings suggest that some of the deleterious effects of consumption of endophyte-infected tall fescue, which contains several ergot alkaloids including ergovaline, may be due to D2 dopamine receptor activation.

G protein-coupled P2 purinoceptors: from molecular biology to functional responses

Nucleotides such as ATP and ADP act as intercellular messengers and exert a widespread influence on cellular function by acting on a variety of cell surface receptors. Until recently, progress has been restrained, in part, by a lack of cloned receptors. Now, however, the successful cloning of a variety of P2 purinoceptors is holding out the prospect of rapid advances in the understanding of this diverse group of receptors and the potent therapeutic resource they represent. In this article, Michael Boarder and colleagues summarize the findings of recent cloning studies, and assess the impact of these on the understanding of the function of the G protein-coupled P2 purinoceptors in several types of cells and tissues.

Site-directed mutagenesis of P2U purinoceptors. Positively charged amino acids in transmembrane helices 6 and 7 affect agonist potency and specificity

Two subtypes of G protein-coupled receptors for nucleotides (P2U and P2Y purinoreceptors) contain several conserved positively charged amino acids in the third, sixth, and seventh putative transmembrane helices (TMHs). Since the fully ionized form of nucleotides has been shown to be an activating ligand for both P2U and P2Y purinoceptors (P2UR and P2YR), we postulated that some of these positively charged amino acids are involved in binding of the negatively charged phosphate groups of nucleotides. To investigate the role of the conserved positively charged amino acids in purinoceptor function, a series of mutant P2UR cDNAs were constructed so that lysine 107 and arginine 110 in TMH 3, histidine 262 and arginine 265 in TMH 6, and arginine 292 in TMH 7 were changed to the neutral amino acid leucine or isoleucine. The mutated P2UR cDNAs were stably expressed in 1321N1 astrocytoma cells and receptor activity was monitored by quantitating changes in the concentration of intracellular Ca2+ upon stimulation with full (ATP, UTP) or partial (ADP, UDP) P2UR agonists. Neutralization of His262, Arg265, or Arg292 caused a 100-850-fold decrease in the potency of ATP and UTP relative to the unmutated P2UR and rendered ADP and UDP ineffective. In contrast, neutralization of Lys107 or Arg110 did not alter the agonist potency or specificity of the P2UR. Neutralization of Lys289 in the P2UR, which is expressed as a glutamine residue in the P2Y subtype, did not alter receptor activity; however, a conservative change from lysine to arginine at this position altered the rank order of agonist potency so that ADP and UDP were approximately 100-fold more potent than ATP and UTP. A three-dimensional model of the P2UR indicates the feasibility of His262, Arg265, and Arg292 interactions with the phosphate groups of nucleotides.

D2 dopamine receptor response to endophyte-infected tall fescue and an antagonist in the rat

Effects on rat brain D2 dopamine receptors by endophyte-infected tall fescue seed consumption and antagonist injection were characterized. Forty-eight male Wistar rats (225 g) in three separate trials were exposed to either 22 or 32 degrees C. Diets, to maintain similar concentrations of ergovaline, contained 10% (Trial 1) or 15% (Trials 2 and 3) endophyte-infected (E+; 325 average ppb of ergovaline) or uninfected (E-; 0 ppb of ergovaline) tall fescue seed. Rats were injected i.p. daily with either placebo (PL) or an experimental D2 dopamine antagonist (DA, .0375 mg/kg BW). No effects (P > .10) on diet DM intake by E+ ingestion or DA injection were detected at 22 degrees C. However, ingestion of E+ reduced (P < .01) and injection of DA improved (P < .05) DM intake of rats housed in 32 degrees C (11.1 vs 15.4 g of DM/d for E+ vs E-, respectively). Whole brain D2 dopamine receptor density (Bmax) and mRNA were reduced (P < .05) by E+ and increased (P < .05) by DA in Trial 1. No treatment effects (P > .10) on cerebral cortex alpha 1- and alpha 2-adrenergic or striatal D2 dopamine receptor Bmax were measured in Trials 2 and 3. In summary, dietary E+ reduced whole brain D2 dopamine mRNA and Bmax, whereas injection of DA increased D2 dopamine mRNA. Thus, long-term regulation of monoamine receptors seems to be affected by E+ ingestion or DA injection.

Cloning and expression of a human P2U nucleotide receptor, a target for cystic fibrosis pharmacotherapy

The Cl- secretory pathway that is defective in cystic fibrosis (CF) can be bypassed by an alternative pathway for Cl- transport that is activated by extracellular nucleotides. Accordingly, the P2 receptor that mediates this effect is a therapeutic target for improving Cl- secretion in CF patients. In this paper, we report the sequence and functional expression of a cDNA cloned from human airway epithelial (CF/T43) cells that encodes a protein with properties of a P2U nucleotide receptor. With a retrovirus system, the human airway clone was stably expressed in 1321N1 astrocytoma cells, a human cell line unresponsive to extracellular nucleotides. Studies of inositol phosphate accumulation and intracellular Ca2+ mobilization induced by extracellular nucleotides in 1321N1 cells expressing the receptor identified this clone as the target receptor in human airway epithelia. In addition, we independently isolated an identical cDNA from human colonic epithelial (HT-29) cells, indicating that this is the same P2U receptor that has been functionally identified in other human tissues. Expression of the human P2U receptor (HP2U) in 1321N1 cells revealed evidence for autocrine ATP release and stimulation of transduced receptors. Thus, HP2U expression in the 1321N1 cell line will be useful for studying autocrine regulatory mechanisms and in screening of potential therapeutic drugs.

Integrative Cloning, Expression, and Stability of the cryIA(c) Gene from Bacillus thuringiensis subsp. kurstaki in a Recombinant Strain of Clavibacter xyli subsp. cynodontis

A bacterial endophyte was engineered for insecticidal activity against the European corn borer. The cryIA(c) gene from Bacillus thuringiensis subsp. kurstaki was introduced into the chromosome of Clavibacter xyli subsp. cynodontis by using an integrative plasmid vector. The integration vectors pCG740 and pCG741 included the replicon pGEM5Zf(+), which is maintained in Escherichia coli but not in C. xyli subsp. cynodontis; tetM as a marker for selection in C. xyli subsp. cynodontis ; and a chromosomal fragment of C. xyli subsp. cynodontis to allow for homologous recombination between the vector and the bacterial chromosome. Insertion of vector DNA into the chromosome was demonstrated by DNA hybridization. Recombinant strains MDR1.583 and MDR1.586 containing the cryIA(c) gene were shown to produce the 133,000-kDa protoxin and several smaller immunoreactive proteins. Both strains were equally toxic to insect larvae in bioassays. Significant insecticidal activity was demonstrated in planta. The cryIA(c) gene and the tetM gene introduced into strain MDR1.586 were shown to be deleted from some cells, thereby giving rise to a noninsecticidal segregant population. In DNA hybridization experiments and insect bioassays, these segregants were indistinguishable from the wild-type strain. Overall, these results demonstrate the plausibility of genetically engineered bacterial endophytes for insect control.

Functional expression and photoaffinity labeling of a cloned P2U purinergic receptor

ATP and UTP can function as extracellular signaling molecules by activating plasma membrane receptors termed P2 purinergic receptors. In the present study a P2U receptor cDNA has been expressed in K-562 human leukemia cells, one of the few available mammalian cell lines that lacks an endogenous P2U receptor. In stably transfected cells, low micromolar concentrations of ATP or UTP activated the receptor, resulting in the mobilization of intracellular calcium but not the influx of extracellular calcium. A photoaffinity agonist of the P2U receptor, 3'-O-(4-benzoylbenzoyl)adenosine 5'-[alpha-32P]triphosphate ([alpha-32P]BzATP), photolabeled several proteins in plasma membranes from the stable transfectant or from untransfected K-562 cells. The photolabeling of a 53-kDa protein was significantly greater in plasma membranes from the stable transfectant than from untransfected cells. A mutant receptor containing six consecutive histidine residues at its carboxyl terminus was constructed and used to verify that this 53-kDa protein was the P2U receptor. In plasma membranes from cells expressing the histidine-tagged P2U receptor, but not from cells expressing the wild-type receptor, a single [alpha-32P]BzATP-labeled protein with a molecular mass of 53 kDa was retained on a Ni(2+)-charged Sepharose column, which binds many proteins containing a polyhistidine tag. Photolabeling of the 53-kDa protein by [alpha-32P]BzATP was inhibited by ATP but not by UTP, raising the possibility that the P2U receptor may have distinct binding sites for each nucleotide.

Guanylin stimulation of Cl- secretion in human intestinal T84 cells via cyclic guanosine monophosphate

Intestinal salt and fluid secretion is stimulated by Escherichia coli heat-stable enterotoxins (ST) through activation of a membrane guanylate cyclase found in the intestine. Guanylin is an endogenous intestinal peptide that has structural similarity to the bacterial peptides. Synthetic preparations of guanylin or E. coli ST 5-17 stimulated Cl- secretion in T84 cells cultured on semipermeable membranes as measured by increases in short circuit current (Isc). The guanylin/ST receptors appeared to be on the apical surface of T84 cells, since addition of guanylin to the apical, but not basolateral, reservoir stimulated Isc. Bumetanide added to the basolateral side effectively inhibited the Isc responses of T84 cells to either guanylin or ST 5-17. Guanylin appeared to be about one-tenth as potent as ST in stimulating transepithelial Cl- secretion. Guanylin and E. coli ST 5-17 both caused massive (> 1,000-fold) increases in cGMP levels in T84 cells, but guanylin was less potent than ST. Both peptides fully inhibited the binding of 125I-ST to receptor sites on intact T84 cells. The radioligand binding data obtained with guanylin or ST 5-17 best fit a model predicting two receptors with different affinity for these ligands. The Ki values for guanylin were 19 +/- 5 nM and 1.3 +/- 0.5 microM, whereas the Ki values for ST 5-17 were 78 +/- 38 pM and 4.9 +/- 1.4 nM. We conclude that guanylin stimulated Cl- secretion via the second messenger, cGMP, in T84 human colon cells. At least two guanylin receptors with different affinities for these ligands may exist in the cultured T84 cells. It may be postulated that guanylin is an endogenous hormone that controls intestinal Cl- secretion by a paracrine mechanism via cGMP and that E. coli ST stimulates Cl- secretion by virtue of an opportunistic mechanism through activation of guanylin receptors.

Recidivism and mental illness: the role of communities

This study examined the impact of community characteristics on rehospitalization of chronically mentally ill (CMI) clients from public psychiatric hospitals in Virginia. The relationship between rehospitalization, often termed recidivism, and community attributes was explained within the theoretical context of community ecology (Hawley 1950). A small area analysis approach that employed path analysis was used to assess the relationship between rehospitalization and selected community variables including: available health care resources, socioeconomic factors, race, presence of psychopathology, and household composition. The path model was estimated and validated using a linear structural relations computer program (LISREL VI). Results reveal female-headed households and socioeconomic status to be significant predictors of rehospitalization. A discussion of implications of the findings for community mental health services delivery and research is provided.

Potentiation of cyclic adenosine monophosphate production by thrombin in the human erythroleukemia cell line, HEL

The human erythroleukemia cell line (HEL) has been used as a model system for studying signal transduction processes as they might relate to platelet/megakaryocyte function. We were interested in examining the role of thrombin in the regulation of adenylyl cyclase in this cell line. As opposed to its predominantly inhibitory effects on cyclic AMP production in platelets or in membranes from HEL cells, our initial experiments in intact HEL cells revealed that thrombin markedly potentiated the cyclic AMP response to prostaglandin E1 (2.9 +/- 0.2-fold), prostacyclin (1.9 +/- 0.2-fold) and carbacyclin (2.5 +/- 0.5-fold), measured either by radioimmunoassay or by the [3H]adenine preloading procedure. Thrombin, although ineffective alone, also potentiated cyclic AMP production stimulated by vasoactive intestinal peptide (1.6 +/- 0.2-fold), cholera toxin (3.0 +/- 0.6-fold) and AIF4- (2.3 +/- 0.6-fold), but not by forskolin (0.9 +/- 0.1-fold). The thrombin effect 1) produced an increase in the efficacy of the prostaglandins with no change in potency; 2) was long-lived; 3) required the proteolytic activity of thrombin; 4) was insensitive to pertussis toxin; and 5) was at least partially mimicked by trypsin, extracellular ATP and UTP, platelet activating factor and activators of protein kinase C. Down-regulation of protein kinase C or pre-exposure to the protein kinase inhibitor staurosporine blocked the potentiating effect. Together, these results suggest that in HEL cells, the mechanism of thrombin potentiation of cyclic AMP production may involve alterations in the interaction between stimulatory guanine nucleotide binding protein and the catalytic subunit of adenylyl cyclase, possibly involving protein kinase C-mediated phosphorylation.

Regulation of secretion by vasoactive intestinal peptide in isolated perfused rat submandibular glands

The isolated, perfused gland was used to examine the regulation of saliva volume and protein content by vasoactive intestinal peptide (VIP). In the absence of other secretagogues, VIP produced a modest, sustained saliva flow with a biphasic dose-response curve in which saliva volume was greatest at 1 nM VIP (28.5 +/- 3.8 microliters in the first 5 min, n = 4) but reduced at lower and higher concentrations. The protein concentration in saliva released in response to VIP (0.86 +/- 0.13 micrograms/microliters) was substantially higher than with 30 nM acetylcholine (0.06 +/- 0.02 micrograms/microliters) or 1 nM substance P (0.30 +/- 0.05 micrograms/microliters). During the first 5 min of stimulation, VIP and substance P were synergistic in terms of volume and protein content whereas inclusion of VIP did not increase acetylcholine-stimulated flow in the first 5 min but produced a higher sustained flow over the next hour. After stimulation with acetylcholine, subsequent addition of VIP transiently enhanced saliva volume and protein content in a monophasic, dose-dependent manner with effects at 1 pM VIP and higher. The responses were different for VIP compared with other cAMP-mobilizing agents and the involvement of multiple VIP receptor subtypes was suggested from experiments in which a VIP antagonist blocked the VIP enhancement of saliva volume but not the increase in protein.

Functional studies in the human submandibular duct cell line, HSG-PA, suggest a second salivary gland receptor subtype for nucleotides

Extracellular nucleotides, acting through P2 purinoceptors, have been implicated in the regulation of ion transporting epithelia, including salivary gland acini. Multiple P2 purinoceptor subtypes have been suggested, including P2X, P2Y and P2U (or nucleotide) subtypes, as well as the P2Z subtype found in rat parotid acinar cells. We investigated responses to ATP, ATP analogs and UTP in transformed human submandibular gland duct cells (HSG-PA), in order to compare duct cell purinoreceptors with those in acinar cells. ATP, UTP and some ATP analogs increased, with different potencies, inositol phosphate accumulation, calcium mobilization and potassium efflux. Nucleotide-stimulated calcium mobilization occurred in the absence of, but was enhanced by, extracellular calcium, and maximal potassium efflux required extracellular calcium. UTP and ATP demonstrated equal potencies of about 1 microM and similar efficacies in eliciting these responses, and identical rank orders of potency for stimulating calcium mobilization and potassium efflux were obtained: UTP = ATP greater than ATP gamma S greater than ADP greater than ADP beta S, with alpha,beta-methylene-ATP and 2-methylthio-ATP having little or no effect. Agents reported to block nucleotide effects in parotid acini were ineffective in HSG-PA cells, and experiments in Mg(++)- and Ca(++)-free medium did not indicate that a form of ATP other than MgATP was the active species at the HSG-PA purinoceptor. The extracellular nucleotide effects were not altered by pertussis toxin. These results indicate the presence of a P2U or nucleotide receptor subtype in HSG-PA submandibular duct cells distinguishable from the P2Z purinoceptor of rat parotid acinar cells, suggesting involvement of multiple nucleotide receptor subtypes in salivary gland regulation.

Stability of the delta-endotoxin gene from Bacillus thuringiensis subsp. kurstaki in a recombinant strain of Clavibacter xyli subsp. cynodontis

Deletion of chromosomally inserted gene sequences from Clavibacter xyli subsp. cynodontis, a xylem-inhabiting endophyte, was studied in vitro and in planta. We found that nonreplicating plasmid pCG610, which conferred resistance to kanamycin and tetracycline and contained segments of C. xyli subsp. cynodontis genomic DNA, integrated into a homologous sequence in the bacterial chromosome. In addition, pCG610 contains two copies of the gene encoding the CryIA(c) insecticidal protein of Bacillus thuringiensis subsp. kurstaki HD73. Using drug resistance phenotypes and specific DNA probes, we found that the loss of all three genes arose both in vitro under nonselective conditions and in planta. The resulting segregants are probably formed by recombination between the repeated DNA sequences flanking pCG610 that resulted from the integration event into the chromosome. Eventually, segregants predominated in the bacterial population. The loss of the integrated plasmid from C. xyli subsp. cynodontis revealed a possible approach for decreasing the environmental consequences of recombinant bacteria for agricultural use.