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L J Wallace

Publications and source records attributed to L J Wallace.

At least 73 records · Page 4Linked to original sources
PubMed1990

The Z-DNA motif d(TG)30 promotes reception of information during gene conversion events while stimulating homologous recombination in human cells in culture.

Tracts of the alternating dinucleotide polydeoxythymidylic-guanylic [d(TG)].polydeoxyadenylic-cytidylic acid [d(AC)], present throughout the human genome, are capable of readily forming left-handed Z-DNA in vitro. We have analyzed the effects of the Z-DNA motif d(TG)30 upon homologous recombination between two nonreplicating plasmid substrates cotransfected into human cells in culture. In this study, the sequence d(TG)30 is shown to stimulate homologous recombination up to 20-fold. Enhancement is specific to the Z-DNA motif; a control DNA fragment of similar size does not alter the recombination frequency. The stimulation of recombination is observed at a distance (237 to 1,269 base pairs away from the Z-DNA motif) and involves both gene conversion and reciprocal exchange events. Maximum stimulation is observed when the sequence is present in both substrates, but it is capable of stimulating when present in only one substrate. Analysis of recombination products indicates that the Z-DNA motif increases the frequency and alters the distribution of multiple, unselected recombination events. Specifically designed crosses indicate that the substrate containing the Z-DNA motif preferentially acts as the recipient of genetic information during gene conversion events. Models describing how left-handed Z-DNA sequences might promote the initiation of homologous recombination are presented.

Animals↗
PubMed1990

Effects of thromboxane A2 on thoracic aorta of young and old rats: use of selective thromboxane receptor antagonists.

Thromboxane A2 (TXA2) is a bioactive metabolite of arachidonic acid which produces vascular smooth muscle contraction and blood platelet aggregation. The goal of this study is to establish whether there are age-dependent differences of vascular contractility to TXA2. Thoracic aorta of F-344 rats of age 4-6 months (young) and 22-23 months (old) were used as a model to examine responses to U46619 [(15S)-hydroxy-11 alpha, 9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid; a TXA2 agonist] alone or in the presence of prostanoid (SQ 29,548) or nonprostanoid (trimetoquinol, TMQ) endoperoxide/TXA2 receptor antagonists. Maximal contractile responses (84 and 89% relative to KCl) and EC50 values (23 and 55 nmol/l, respectively) to U46619 were the same in aortic strips of young and old animals. Experimentally determined pA2 and pKB values for SQ 29,548 and TMQ as antagonists of U46619-mediated contraction were unchanged in aorta of young (9.09 and 5.83, respectively) and old (9.41 and 6.10, respectively) rats. We conclude that the reactivity and population of TXA2 receptors in rat vascular smooth muscle are unaffected by the aging process.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1990

Characterization of Ile,Ser-bradykinin-induced changes in short-circuit current across rat colon.

The effects of Ile,Ser-bradykinin (TK) on electrolyte secretion across mucosa of rat distal colon were determined and compared to those of bradykinin (BK). A segment of colon stripped of muscularis was mounted in an Ussing chamber for monitoring short-circuit current (Isc). Serosal application of TK and BK produced a concentration-dependent and transient increase in Isc with EC50(nM) values of 2.0 +/- 0.6 and 1.7 +/- 0.7, respectively. At a concentration of 1.0 microM, TK produced a maximal response of 130 +/- 18 compared to 75 +/- 13 microA/cm2 for BK. Increases in Isc induced by BK and TK were significantly (P less than .001) inhibited (90 +/- 4% for BK and 87 +/- 5% for TK) by serosal addition of bumetanide (10 microM). The lipoxygenase/cyclooxygenase inhibitor, eicosa-5,8,11,14-tetraynoic acid (0.1 mM), inhibited (P less than .01) the response to BK by 67 +/- 9% and to TK by 51 +/- 8%. Moreover, the cyclooxygenase inhibitor indomethacin (5.0 microM) significantly (P less than .05) inhibited the Isc response to 1.0 nM BK and 1.0 nM TK. Atropine (1.0 microM) did not block the effects of either kinin. Finally, the BK antagonist D-Arg0[Hyp3,Thi5,8,DPhe7]-bradykinin (2.0 microM) competitively antagonized the effect of BK and TK, shifting the concentration curve competitively to the right by 6-fold and 16-fold respectively. Another BK antagonist, [D-Phe7]-bradykinin (20 microM), also exhibited similar blockade effects. In this model, although some differences exist, BK and TK appear to act by the same mechanism, which may involve arachidonic acid metabolites.

Animals↗
PubMed1989

Sensory nerves and urinary bladder function: effects of diabetes, capsaicin and acrylamide treatment.

1. A comparison was made of the proposed neurotoxic effects of acrylamide, capsaicin, and diabetes on rat urinary bladder pressure responses elicited by infusion of buffer into the organ (distension). 2. Treatment with capsaicin or acrylamide completely abolished the bladder pressure responses. 3. After 4 weeks of diuresis equivalent to that of the diabetic model, the pressure response was markedly diminished compared to control. This response was greatly increased following L-DOPA, which augments the micturition reflex. 4. After 4 weeks of streptozoticin-induced diabetes, the pressure response was slightly diminished compared to control and most closely resembled the response from the diuretic group treated with L-DOPA.

Acrylamides↗
PubMed1989

Effects of age on urinary bladder function in the male rat.

In a previous study we investigated the effects of age on the micturition characteristics and bladder function of male Fischer rats ages five to seven, 16 to 18 and 22 to 24 months. The 24 hr. water intake and urine output increases significantly with age; 22 to 24 month rats showed a 39% increase in water intake and a 93% increase in urine output compared to five to seven month rats. The intravesical pressure at micturition is 100% greater in 22 to 24 month and 16 to 18 month rats compared to five to seven month old rats with no age-related change in bladder volume at micturition. In the present study, in vitro bladder capacity did not differ between the three age groups although the average plateau pressure significantly decreased with advancing age. Using the isolated whole bladder model, the contractile response to the autonomic agonists bethanechol, phenylephrine, and isoproterenol did not change significantly with age. Similarly, there were no age-related changes in the response of the bladder to non-autonomic drugs (histamine, oxytocin, serotonin, substance P, and PGF2 alpha) except for PGF2 alpha which produced an age-related increase in the maximum bladder contraction. In summary, while in vivo micturition clearly changes with age, the in vitro contractility of the bladders to autonomic agents did not. Therefore, age related differences in micturition would be related primarily to the changes in neuronal innervation and central control of micturition rather than alterations in the contractility of the bladder. In addition, these studies show the importance of correlating in vivo bladder function (micturition frequency and volume, cystometry and urodynamics) with in vitro contractile and functional studies.

Aging↗
PubMed1989

Synthesis and D2 dopaminergic activity of pyrrolidinium, tetrahydrothiophenium, and tetrahydrothiophene analogues of sulpiride.

All of the existing dopamine receptor models recognize the amine nitrogen of agonist and antagonist drugs as playing a crucial role in receptor interactions. However, there has been some controversy as to which molecular form of the amine, charged or uncharged, is most important in these interactions. We have synthesized and examined the biological activity of permanently charged and permanently uncharged analogues of the dopaminergic antagonist, sulpiride. Sulpiride and the permanently charged pyrrolidinium (6,7) and tetrahydrothiophenium (9) analogues were able to antagonize the inhibitory effect of apomorphine on the K+-induced release of [3H]acetylcholine from striatal slices. In contrast, the permanently uncharged tetrahydrothiophene analogue 8 was inactive at concentrations up to 100 microM. Additionally, both sulpiride and the tetrahydrothiophenium analogue were able to displace [3H]spiperone from D2 binding sites, while the tetrahydrothiophene analogue was unable to produce any significant displacement. These results are consistent with our previous observations on permanently charged chlorpromazine analogues and provide further evidence that dopaminergic antagonists bind in their charged molecular forms to anionic sites on the D2 receptor.

Acetylcholine↗
PubMed1989

Effects of diabetes and diuresis on contraction and relaxation mechanisms in rat urinary bladder.

Experiments were designed to gain information on the mechanisms leading to diabetic urinary bladder dysfunction. Bladders from control rats, animals subjected to 4-5 wk streptozocin-induced diabetes, and rats subjected to equivalent diuresis produced by 5% sucrose feeding were studied with an in vitro whole-bladder preparation and neurochemical measurements. The diuretic group was used to distinguish alterations produced by metabolic effects on nerve and muscle from those induced by prolonged periods of excessive diuresis. Diuresis alone explains many of the diabetes-induced effects, including decreased norepinephrine levels, postsynaptic supersensitivity for sympathetic regulation of bladder storage, decreased responsiveness to parasympathetic regulation of emptying, and enhanced prostaglandin F2 alpha-induced contraction. Other diabetes-induced effects were not observed in the diuretic controls and are presumed to result from metabolic alterations associated with diabetes. These effects were decreases in norepinephrine uptake and in choline acetyltransferase activity, both markers of nerve terminal function. Thus, diuretic and metabolic factors appear to contribute to the early signs of parasympathetic and sympathetic neuropathy. In contrast, we found no evidence for loss of sensory nerve function in the diabetic bladder, at least at the organ level, because no diabetes- or diuresis-induced changes were observed in responsiveness to substance P or capsaicin.

Aminophylline↗
PubMed1988

Characterization of the inhibition of U46619-mediated human platelet activation by the trimetoquinol isomers. Evidence for endoperoxide/thromboxane A2 receptor blockade.

Sites of inhibition for the trimetoquinol (TMQ) isomers on 15S-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid (U46619)-, 12-O-tetradecanoylphorbol 13-acetate (TPA)- and A23187-induced human platelet activation were investigated. Experiments using washed human platelets were designed to characterize relationships among functional (aggregation, secretion) and biochemical (protein phosphorylation, metabolism of inositol phospholipids and radioligand displacement analysis) processes of platelet activation by U46619 and the specificity of inhibition by the TMQ isomers. Thromboxane A2 receptor stimulation by U46619 in human platelets resulted in a time- and concentration-dependent breakdown of inositol phospholipids [phosphatidylinositol 4,5-bisphosphate (PIP2), phosphatidylinositol 4-monophosphate (PIP), and phosphatidylinositol (PI)], phosphatidic acid (PA) accumulation, phosphorylation of 20 and 45 kD proteins, aggregation and serotonin secretion. The TMQ isomers stereoselectively inhibited all U46619-mediated platelet activation processes. R(+)-TMQ was 40- and 22-fold more potent than S(-)-TMQ as an inhibitor of U46619-induced platelet aggregation and serotonin secretion respectively. In addition, R(+)-TMQ blocked U46619-induced 20 kD protein phosphorylation, 45 kD protein phosphorylation, PIP2, PIP and PI breakdown, and PA accumulation with a potency which was 8-, 13-, 45-, 37-, 33- and 33-fold greater than the S(-)-isomer respectively. In contrast to S(-)-TMQ, R(+)-TMQ produced a concentration-dependent inhibition of specific [3H]U46619 binding to endoperoxide/thromboxane A2 receptor sites in washed platelets. In other experiments, S(-)-TMQ was more potent than R(+)-TMQ as an inhibitor of TPA- and A23187-induced platelet aggregation and serotonin secretion, and of TPA-induced phosphorylation of 45 and 20 kD proteins. The inhibitory potencies of S(-)-TMQ against TPA- or A23187-induced responses were similar to those needed for antagonism of U46619-mediated platelet activation. In contrast, much higher concentrations of R(+)-TMQ were required for blockade of TPA or A23187 versus U46619-mediated responses in human platelets. Taken collectively, the data show that the TMQ isomers interfered with the endoperoxide/thromboxane A2 receptor-mediated phospholipase C-signal cascade of inositol phospholipid hydrolysis, calcium mobilization, and protein phosphorylation leading to platelet aggregation and secretion. R(+)-TMQ acted as a pharmacologically selective and highly stereospecific [R(+)-TMQ much greater than S(-)-TMQ] antagonist of endoperoxide/thromboxane A2 receptor sites in platelets.(ABSTRACT TRUNCATED AT 400 WORDS)

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1988

Use of [3H]trimetoquinol as a radioligand in human platelets: interaction with putative endoperoxide/thromboxane A2 receptor sites.

We have recently shown that trimetoquinol [1-(3,4,5-trimethoxybenzyl)-6,7-dihydroxy-1,2,3,4- tetrahydroisoquinoline; TMQ] is a potent and stereoselective [R(+)-isomer greater than S(-)-isomer] antagonist of aggregation induced by thromboxane A2 and stable epoxymethano PGH2 analogues (U46619; U44069) in human platelets. The present study was undertaken to characterize the pharmacological specificity of binding sites for racemic- [3H]TMQ in washed human platelets. Specific binding of [3H]TMQ, determined by addition of 100 microM R(+)-TMQ, accounted for 12-26% of the total binding at 1.0 microM. Saturation data suggested two binding sites with apparent dissociation constants of 2.8 nM and 1.4 microM for the high and low affinity binding sites, respectively. Maximal binding densities (pmol/mg protein) were 2.3 and 42.9 for the respective high and low affinity sites. The optical isomers of TMQ, cis and trans-isomers of 13-azaprostanoic acid (13-APA), and U46619 inhibited [3H]TMQ specific binding to the low affinity site. R(+)-TMQ was 32-fold more potent than S(-)-TMQ at inhibiting [3H]TMQ binding, and the stereoselective potency difference and concentrations needed to inhibit binding were similar to those required for inhibition of U46619-induced platelet aggregation and serotonin secretion. Similarly, trans-13-APA was 90-fold more potent than cis-13-APA as a competitor of [3H]TMQ binding. U46619 also inhibited TMQ binding at concentrations (IC50 = 0.4 microM) similar to those required for aggregation (EC50 = 0.16 microM) and secretion (EC50 = 0.23 microM). At 1 mM, arachidonic acid inhibited [3H] TMQ binding by only 25%. Our studies indicate that [3H]TMQ interacts with specific binding sites with characteristics indicative of putative endoperoxide/thromboxane A2 receptors in human platelets.

Blood Platelets↗
PubMed1988

Regional noradrenergic and cholinergic neurochemistry in the rat urinary bladder: effects of age.

Neurochemistry of the base and body of the rat urinary bladder was compared for both adrenergic and cholinergic parameters using Fischer 344 rats. In bladder base and body, respectively, the concentration (pmol./mg. wet weight) of norepinephrine was 23.4 and 2.16, of acetylcholine was 26.7 and 18.3, and of choline was 96.7 and 199. The activity (nmol./mg. protein/hour) of tyrosine hydroxylase was 422 and less than 50, of monoamine oxidase was 80.6 and 126, of choline acetyltransferase was 17.4 and 11.5, and of acetylcholinesterase (nmol./mg. wet weight/hour) was 485 and 165. Treatment with alpha-methyl-p-tyrosine did not alter norepinephrine concentration in bladder base but decreased it by 27% in bladder body. Studies were also done to determine whether age-related changes exist in the adrenergic and cholinergic neurochemistry of the rat urinary bladder. Bladders from rats of 6-7, 15-17, and 22-24 mo. of age were examined. The only age-related differences noted were a progressive decrease in level of monoamine oxidase activity in both bladder regions and an increase in bladder base norepinephrine concentration from 6-7 to 15-17 mo. followed by a decrease at 22-24 mo. Overall, the results show marked regional variations in bladder neurochemistry which remain remarkably stable as the animals grow old.

Acetylcholine↗
PubMed1988

Effect of age on in vivo urinary bladder function in the rat.

The effects of age on micturition in male Fischer 344 rats, ages five to seven, 16 to 18 and 22 to 24 months, were studied. The 24 hr. water intake, 24 hr. urine output, frequency and volume of each micturition were obtained from rats housed individually in metabolic cages. Intravesical pressure and volume at which the micturition contraction occurred were evaluated using natural-fill cystometry. The 24 hr. water intake and urine output increased significantly with advancing age; 22 to 24 months rats showed a 39% increase in water intake and a 93% increase in urine output compared to five to seven month rats. The increase in urine output observed in the 22 to 24 month old rats was manifested by a 95% increase in volume per micturition and a 52% increase in frequency of micturition compared to five to seven month old rats. The pressure at micturition (PAM) was 100% greater in 22 to 24 and 16 to 18 month old rats compared to five to seven month old rats with no age-related difference in bladder volume at micturition (BVM). These studies demonstrate that in vivo micturition changes with age in the male F344 rat. Although there were no overt urological dysfunctions observed in the aging rats, the alterations in function would indicate that there were changes in either the mechanisms controlling micturition, or changes in the musculature itself. These possibilities will be the subject of further investigations.

Aging↗
PubMed1988

Diabetes and diuretic-induced alterations in function of rat urinary bladder.

Studies were done to characterize the bladder dysfunction associated with diabetes mellitus and to distinguish between changes occurring from increased diuresis and autonomic neuropathy. Four experimental conditions were compared: control, 4-wk-streptozocin-induced diabetes, sucrose feeding (diuretic), and galactose feeding (diuretic and sugar alcohol). A 10-fold increase in urine output and 25-50% increases in bladder weight, protein content, and DNA content were observed in all noncontrol treatment groups. Compliance properties were studied by measuring the intravesicular pressure as the bladder was infused with buffer in vitro. All treated bladders exhibited a reduction in plateau pressure and an increase in fluid capacity. Thus, diuresis results in an increased bladder size, which correlates with an alteration of compliance properties. Nervous system control in anesthetized rats was examined by monitoring contractions as the bladder was infused with buffer. Three distinct patterns of response were observed: normal, diabetic, and diuretic (galactose and sucrose treatments). The difference between responses in diuretic and diabetic animals suggests the presence of a diabetes-induced alteration in nerve regulation of the bladder. Reserpine pretreatment of control or diuretic models produced marked changes in the pattern of contractions, whereas pretreatment of diabetic rats had only modest effects. This suggests that diabetic bladders were lacking sympathetic control before the drug treatment. When rats treated for 4 wk with galactose were removed from this diet for 4 wk before testing, the bladders responded similarly to controls. This observation, coupled with the fact that galactose did not produce the same response as diabetes in the in vivo experiment, suggests that the galactose model does not produce irreversible functional neuropathies.

Animals↗
PubMed1987

Exogenous ATP-stimulated calcium uptake in isolated rat intestinal epithelial cells.

ATP in the extracellular medium is known to stimulate Ca uptake into avian intestinal epithelial cells. We have now demonstrated a similar effect of ATP in mammalian intestinal epithelial cells and have further characterized this effect. Exogenous ATP increased 45Ca uptake 2-6 fold in isolated rat small intestinal epithelial cells, with a maximal effect at 1 mM and an ED50 of 290 microM. A strict structural requirement for nucleotide-stimulated 45Ca uptake was observed. ADP was much less effective than ATP and gamma-thio-ATP, and 5'-AMP, cyclic AMP, adenosine, non-adenine nucleotides, non-hydrolyzable ATP analogs and ATP analogs with ring substitutions at the 8 position were inactive. Prenylamine (100 microM) completely inhibited ATP-stimulated 45Ca uptake, while verapamil (100 microM) had only a small effect. In the intact intestine, ATP increased short-circuit current (Isc) when added to the mucosal side of the tissue. This effect was reduced by 10 microM and abolished by 100 microM prenylamine. The effect of ATP on Isc was markedly reduced in Cl-free solutions and in reduced-Ca solutions. Serosal and mucosal addition of the nonhydrolyzable ATP analog, beta, gamma-methylene-ATP, and serosal addition of ATP had little or no effect on Isc. The similarities between the effects of ATP in isolated cells and in the intact intestine suggest that the effect of ATP on Isc may be at least partially mediated through stimulation of Ca uptake into the epithelial cells.

Adenosine Triphosphate↗
PubMed1987

Charged analogues of chlorpromazine as dopamine antagonists.

Chlorpromazine (1, CPZ) is a potent dopamine antagonist that has been used widely as an antipsychotic agent. Since dopaminergic antagonists, like dopaminergic agonists, exist in solution as the charged and uncharged molecular species, it is not clear which form of the amine is most important for interaction with the dopamine receptor. Previous work from our laboratory has indicated that a variety of permanently charged species could replace the amine/ammonium moiety of dopamine and retain dopamine agonist activity. This paper describes the synthesis and dopamine antagonist activity of both the trimethylammonium iodide and the dimethylsulfonium iodide analogues of chlorpromazine. The permanently uncharged methyl sulfide analogue was also synthesized; however, due to its lack of aqueous solubility, its pharmacological activity could not be evaluated. Binding of both the dimethylsulfonium iodide and the trimethylammonium iodide analogues to D-2 dopamine receptors of rat striatal tissue was observed. The observed relative order of binding was CPZ greater than CPZ sulfonium analogue greater than CPZ ammonium analogue. These compounds had a similar order of activity in antagonizing the apomorphine-induced inhibition of potassium-induced release of [3H]acetylcholine from mouse striatal slices.

Acetylcholine↗
PubMed1987

Muscarinic receptor subtypes mediating the mucosal response to neural stimulation of guinea pig ileum.

Muscarinic receptors involved in the secretory response evoked by electrical stimulation of submucosal neurons were investigated in muscle-stripped flat sheets of guinea pig ileum set up in flux chambers. Neural stimulation produced a biphasic increase in short-circuit current due to active chloride secretion. Atropine and 4-diphenylacetoxy-N-methylpiperadine methiodide (4-DAMP) (10(-7) M) were more potent inhibitors of the cholinergic phase of the response than was pirenzepine. Dose-dependent increases in base-line short-circuit current were evoked by carbachol and bethanechol; 4-hydroxy-2-butynyl trimethylammonium chloride (McN A343) produced a much smaller effect. Tetrodotoxin abolished the effects of McN A343 but did not alter the responses of carbachol and bethanechol. McN A343 significantly reduced the cholinergic phase of the neurally evoked response and caused a rightward shift of the carbachol dose-response curve. All muscarinic compounds inhibited [3H]quinuclidinyl benzilate binding to membranes from mucosal scrapings, with a rank order of potency of 4-DAMP greater than pirenzepine greater than McN A343 greater than carbachol greater than bethanechol. These results suggest that acetylcholine released from submucosal neurons mediates chloride secretion by interacting with muscarinic cholinergic receptors that display a high binding affinity for 4-DAMP. Activation of neural muscarinic receptors makes a relatively small contribution to the overall secretory response.

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗
PubMed1987

Cholinergic receptors mediating secretion in guinea pig colon.

This study examined the role of cholinergic receptors in mediating the chloride secretory response evoked by stimulation of enteric neurons in muscle-stripped segments of mucosa from guinea pig distal colon set up in flux chambers. Basal short-circuit current was not altered by tetrodotoxin, hexamethonium or muscarinic antagonists. The neurally evoked response was not altered by hexamethonium, but was reduced by muscarinic antagonists with a rank order of potency: atropine = 4-diphenyl acetoxy-N-methylpiperidine greater than pirenzepine. 1,1-Dimethyl-4-phenyl-piperazinium iodide increased resting short-circuit current above basal levels. Carbachol and bethanechol evoked a concentration-dependent increase in short-circuit current that was reduced by tetrodotoxin. The effects of carbachol were antagonized by hexamethonium, 4-diphenyl acetoxy-N-methylpiperidine and pirenzepine. Competition for [3H]quinuclidinyl benzilate binding indicated a rank order of potency of 4-diphenyl acetoxy-N-methylpiperidine greater than pirenzepine greater than carbachol greater than bethanechol. These studies indicate that cholinergic and noncholinergic transmission play a significant role in regulation of chloride transport in the guinea pig distal colon. Both nicotinic and muscarinic receptors on neurons that project to the mucosa as well as epithelial muscarinic receptors are mediators of the chloride secretory response.

Animals↗