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D A Kendall

Publications and source records attributed to D A Kendall.

At least 109 records · Page 6Linked to original sources
PubMed1993

Adenosine receptor-induced second messenger production in adult guinea-pig cerebellum.

1. The effects of adenosine receptor agonists on cyclic nucleotides accumulation were investigated in adult guinea-pig cerebellar slices by use of radioactive precursors. 2. Adenosine elicited a rapid and maintained increase in cyclic AMP, that was fully reversed upon addition of adenosine deaminase. Adenosine analogues stimulated cyclic AMP generation up to 40 fold with the rank order of potency: 5'-N-ethylcarboxamidoadenosine (0.6 microM) > 2-chloroadenosine (6 microM) > adenosine (13 microM). CGS 21680 (10 microM) elicited only a small stimulation (1.2 fold). 3. The cyclic AMP response to NECA was reversed by the 1,3-dipropylxanthine-based adenosine receptor antagonists 8-[4-[[[[(2-aminoethyl)amino]amino]carbonyl]methyl]oxy]- phenyl]-1,3-dipropylxanthine (XAC), 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) and N-[2-(dimethylamino)ethyl]N-methyl-4-(1,3-dipropylxanthine)benzene sulphonamide (PD 115,199) with estimated apparent inhibition constants of 15, 81 and 117 nM, respectively. 4. Pretreatment with adenosine also potentiated the cyclic GMP response to sodium nitroprusside, abolishing the decline in [3H]-cyclic GMP observed with sodium nitroprusside alone, and allowing [3H]-cyclic GMP levels to be maintained for at least an additional 10 min. This potentiation was fully reversed by adenosine deaminase. 5. Adenosine analogues potentiated the sodium nitroprusside-elicited cyclic GMP generation with the rank order of potency: 5'-N-ethylcarboxamidoadenosine (0.7 microM) > 2-chloroadenosine (6 microM) > adenosine (42 microM). 6. NECA potentiation of cyclic GMP formation was reversed by the antagonists XAC, DPCPX and PD 115,199 with apparent inhibition constants of 17, 102 and 242 nM, respectively. 7. The similar potencies of adenosine analogues and xanthine antagonists for stimulation of cyclic AMP and potentiation of cyclic GMP lead to the suggestion that these phenomena are mediated through the same adenosine receptor, the A2b receptor. Furthermore, we suggest that potentiation of the sodium nitroprusside-induced cyclic GMP response may be mediated at the level of phosphodiesterase hydrolysis of the cyclic nucleotides.

Adenosine↗
PubMed1992

Activation of a metabotropic excitatory amino acid receptor potentiates A2b adenosine receptor-stimulated cyclic AMP accumulation.

Incubation of guinea-pig cerebral cortical slices with the excitatory amino acid agonists DL-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) or N-methyl-D-aspartate (NMDA) failed to significantly alter either basal or 5'-N-ethylcarboxamidoadenosine- (NECA-)stimulated cAMP levels. Quisqualate, L-glutamate and DL-1-aminocyclopentane-trans-1,3- dicarboxylate (t-ACPD) were also without effect on basal levels of cAMP but increased NECA-stimulated levels of cAMP to approximately 190, 220 and 290% of control levels, respectively. Analysis of t-ACPD concentration-response data for the potentiation of NECA-stimulated cAMP elevations and the stimulation of phosphoinositide turnover gave EC50 values of 51 and 107 microM, respectively. The enhancing effect of t-ACPD on cAMP levels was maintained for up to 40 minutes as was the stimulation of phosphoinositide turnover. We conclude that the cAMP response to A2b adenosine receptor stimulation is augmented by the rigid glutamate analogue t-ACPD, possibly through the action of products of phosphoinositide turnover.

Adenosine↗
PubMed1992

Qualitative differences in [Ca2+]i increases and InsP3 generation following stimulation of N1E-115 cells with micromolar and millimolar ATP.

Addition of ATP (100 microM) to populations of the neuronal cell line N1E-115 caused a transient increase in intracellular calcium ([Ca2+]i) which rapidly reached a peak (maximum of 243 +/- 7 nM above basal) and returned to basal after approximately 50 sec. The response was concentration-dependent (EC50 21 +/- 4 microM) and was unchanged when calcium was omitted from the extracellular medium. Transient increases in D-myo-inositol-1,4,5-trisphosphate levels (InsP3) were also observed over a similar time period. Addition of millimolar ATP, however, produced characteristically different responses; [Ca2+]i again increased rapidly (reaching a maximum of 639 +/- 23 nM above basal) but returned to a new maintained plateau (274 +/- 34 nM) which was abolished by the inorganic calcium channel blocker, nickel (1 mM), and omission of calcium from the extracellular medium. InsP3 levels were also maintained but were, however, unaffected by nickel or removal of extracellular calcium. The qualitative difference in the mechanism of calcium elevation produced with millimolar ATP, compared with lower concentrations, suggests that the N1E-115 cells might also contain a low affinity P2 receptor coupled with a calcium channel.

Adenosine Triphosphate↗
PubMed1992

Enhanced catalysis by active-site mutagenesis at aspartic acid 153 in Escherichia coli alkaline phosphatase.

Bacterial alkaline phosphatase catalyzes the hydrolysis and transphosphorylation of phosphate monoesters. Site-directed mutagenesis was used to change the active-site residue Asp-153 to Ala and Asn. In the wild-type enzyme Asp-153 forms a second-sphere complex with Mg2+. The activity of mutant enzymes D153N and D153A is dependent on the inclusion of Mg2+ in the assay buffer. The steady-state kinetic parameters of the D153N mutant display small enhancements, relative to wild type, in buffers containing 10 mM Mg2+. In contrast, the D153A mutation gives rise to a 6.3-fold increase in kcat, a 13.7-fold increase in kcat/Km (50 mM Tris, pH 8), and a 159-fold increase in Ki for Pi (1 M Tris, pH 8). In addition, the activity of D153A increases 25-fold as the pH is increased from 7 to 9. D153A hydrolyzes substrates with widely differing pKa's of their phenolic leaving groups (PNPP and DNPP), at similar rates. As with wild type, the rate-determining step takes place after the initial nucleophilic displacement (k2). The increase in kcat for the D153A mutant indicates that the rate of release of phosphate from the enzyme product complex (k4) has been enhanced.

Alkaline Phosphatase↗
PubMed1992

Agonist-induced changes in [Ca2+]i in N1E-115 cells: differential effects of bradykinin and carbachol.

The addition of bradykinin to populations of fura-2 loaded N1E-115 neuroblastoma cells produced an increase in intracellular calcium which rapidly reached a peak and returned to baseline within 60 s. The response was concentration dependent and unaffected by removal of extracellular calcium or addition of the inorganic channel blocker Ni2+. Similar transient responses were seen with histamine and angiotensin II and experiments monitoring manganese entry suggest that agonist responses in this cell line involve mainly release of calcium from intracellular stores. However, unlike bradykinin, the response to carbachol, at all concentrations, failed to return completely to baseline suggesting a small secondary influx component and highlighting possible differences between the mechanisms of calcium elevation by these two agonists.

Bradykinin↗
PubMed1992

Signal sequences containing multiple aromatic residues.

Using homopolymeric units of either phenylalanine or tryptophan to replace the natural core segment of the Escherichia coli alkaline phosphatase signal peptide, the hydrophobicity requirements for protein export and processing were further explored. The mutant signal peptide containing polyphenylalanine functioned at least as efficiently as the wild-type, while the signal incorporating polytryptophan was dysfunctional. The transport properties of these mutants confirm our work with sequences rich in aliphatic residues; namely that a high mean hydrophobicity per residue is critical for complete and rapid precursor processing and for translocation of the protein. The efficient transport properties of the polyphenylalanine-containing signal peptide demonstrate that neither the bulky, aromatic nature of phenylalanine nor the unusually high hydrophobicity of this mutant peptide adversely alters function. This study also suggests that the low occurrence of phenylalanine in natural signal sequences is not of functional consequence but probably reflects the low number of DNA codons for this residue. The polytryptophan-containing precursor was membrane inserted but not translocated. This type of transport defect suggests that this is a weakly hydrophobic signal peptide, consistent with hydropathy scales, which indicate that tryptophan is comparable to alanine. This application of polymeric sequences provides a function-based assay for the evaluation of amino acid hydrophobicity.

Alkaline Phosphatase↗
PubMed1992

Dopaminergic and serotonergic function following isolation rearing in rats: study of behavioural responses and postmortem and in vivo neurochemistry.

This series of experiments compared isolation-reared and socially reared rats for their locomotor activity, behavioural stereotypy, and monoamine function both postmortem and in vivo using intracerebral dialysis. In Experiment 1, isolates showed an altered time course of locomotor activity following d-amphetamine sulphate (AMPH) administration (0.5, 2.0, 3.0, or 5.0 mg/kg, SC). Isolation-reared rats also showed increased sensitivity to the sedative effects of a low dose of apomorphine hydrochloride (0.1 mg/kg) but did not differ from social controls following higher doses of the drug (0.5, 1.5, or 3.0 mg/kg, SC). Isolates showed a decrease in the intensity of apomorphine-induced stereotyped behaviours but no change in stereotypy induced by AMPH. In Experiment 2, isolates had higher postmortem dopamine (DA) concentrations and an altered asymmetry in DA function in the medial prefrontal cortex (PFC) but not in the nucleus accumbens (NAC) or caudate putamen (CPu). Isolated rats also had a lower 5-hydroxyindoleacetic acid (5-HIAA)/5-hydroxytryptamine (5-HT) ratio in the NAC (but not in the PFC or CPu) compared to controls. Experiment 3 used intracerebral dialysis to examine monoamine function in vivo following isolation rearing. Isolates showed greater increases in extracellular DA and greater decreases in DOPAC in response to 2 mg/kg AMPH SC in both the NAC and CPu. There were no apparent differences in the perfusate concentrations of either dopamine (DA), dihydroxyphenylacetic acid (DOPAC), or homovanillic acid (HVA) prior to drug administration. However, consistent with the results of Experiment 2, isolates had a reduced basal perfusate concentration of 5-HIAA from the NAC but not from the CPu. Experiment 4 measured postsynaptic DA function in CPu tissue slices following isolation. Isolation rearing did not affect cAMP accumulation in response to stimulation of D1 DA receptors by DA (0, 2.7, 9, or 30 microM). In addition, isolation rearing did not affect the coupling between D1 and D2 receptors, as measured by the increase in cAMP accumulation with 1 microM 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1 H-3-benzazepin (SK&F 38393) and its reduction by 10 microM quinperole hydrochloride (LY 171555). These results are discussed in terms of the possible relationship between these neurochemical findings and the behavioural disturbances following isolation rearing of rats.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1992

Biochemical correlates of alpha 1-adrenoceptor activation.

An impressive body of evidence based on radioligand binding, biochemical, functional and structural data supports the existence of two sub-types of the alpha 1-adrenoceptor (alpha 1a and alpha 1b) in the CNS and in peripheral tissues. Both elevate intracellular Ca2+ concentrations, although by different mechanisms, resulting in a cascade of intracellular events dependent upon the cell type involved.

Animals↗
PubMed1992

Excitatory amino acid-induced phosphoinositide turnover in guinea pig cerebral cortical slices: selective enhancement by spermine of the response to DL-1-aminocyclopentane-trans-1,3-dicarboxylate.

In the presence of 1 mM spermine, accumulations of 3H labelled inositol phosphates elicited by quisqualate (100 microM) and 1-aminocyclopentane-trans-1,3-dicarboxylate (t-ACPD, 300 microM) were significantly enhanced by 21 and 26%, respectively, without a significant alteration in the accumulation elicited by L-glutamate (10 mM) or DL-alpha-amino-3-hydroxy-5-methyl-4-isoxalone propionate (10 microM). Analysis of concentration-response data indicated that the presence of spermine led to an increase in the maximal response to t-ACPD without altering the EC50 value. The stimulatory effect of spermine on the accumulation of t-ACPD-elicited 3H-inositol phosphates was not reversed by ifenprodil or diethylenetriamine (putative polyamine site antagonists), by agents that activate or inhibit protein kinase C, or by calcium channel blockade, but was abolished in the presence of elevated extracellular calcium ion concentration. We conclude that spermine enhances the phosphoinositide turnover in guinea pig cerebral cortical slices elicited by the "metabotropic" excitatory amino acid receptor. The site through which the action of spermine is mediated remains to be defined, but it is apparently distinct from that suggested to modulate N-methyl-D-aspartate receptor activity.

Adrenergic alpha-Antagonists↗
PubMed1992

Inhibition of forskolin-stimulated cyclic AMP formation by 1-aminocyclopentane-trans-1,3-dicarboxylate in guinea-pig cerebral cortical slices.

The effects of the selective metabotropic glutamate receptor agonist 1-aminocyclopentane-trans-1,3-dicarboxylate (t-ACPD) on forskolin-stimulated cyclic AMP formation in guinea-pig cerebral cortex slices were determined. t-ACPD inhibited the accumulation of [3H]cyclic AMP by approximately 80%, with an IC50 value of 35 +/- 4 microM. The effect was reversible and stereoselective, with the 1S,3R isomer being approximately 400-fold more potent than the 1R,3S isomer. L-Glutamate (over a restricted concentration range) also partially inhibited the response to forskolin, but quisqualate, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), and N-methyl-D-aspartate (NMDA) were ineffective. The effect of t-ACPD was not blocked by antagonists of the phospholipase C-linked metabotropic glutamate receptor, the AMPA ionotropic glutamate receptor, or the NMDA receptor. In summary, our results indicate the presence of a glutamate receptor in guinea-pig brain that is activated selectively by t-ACPD and that is negatively linked to adenylyl cyclase.

Amino Acids↗
PubMed1992

Direct and indirect stimulations of cyclic AMP formation in human brain.

1. Adenosine 3':5'-cyclic monophosphate (cyclic AMP) formation, by use of an [3H]-adenine prelabelling assay, was measured in fragments of human cerebral cortex, taken in the course of various neurosurgical procedures. 2. Large accumulations of [3H]-cyclic AMP due to isoprenaline, noradrenaline and adenosine and small effects due to forskolin were observed. Histamine, 5-hydroxytryptamine (5-HT) and the excitatory amino acids glutamate and quisqualate were ineffective. 3. The response to noradrenaline consisted of two components; a direct beta-adrenoceptor response and an enhancement mediated by an alpha-adrenoceptor which appears to be similar to that in rat cerebral cortex. 4. The response to isoprenaline was also potentiated by histamine H1 receptor stimulation but the direct effect of 2-chloroadenosine was not altered by histamine, 5-HT or quisqualate. 5. It is concluded that some, but not all, of the indirect modulations of cyclic AMP formation previously observed in experimental animal brain exist in human cerebral cortex.

Adenine↗
PubMed1992

Inositol 1,4,5-trisphosphate generation and calcium mobilisation via activation of an atypical P2 receptor in the neuronal cell line, N1E-115.

1. Alterations in the levels of intracellular calcium ([Ca2+]i) and D-myo-inositol-1,4,5-trisphosphate (InsP3) were measured in the murine neuroblastoma cell line clone, N1E-115, by use of the calcium-sensitive dye, fura-2 and a radioreceptor assay, respectively. 2. Exposure of the cells to ATP (100 microM) elicited rapid and transient increases in [Ca2+]i and InsP3, with both responses reaching a maximum between 10-20 s after agonist addition. 3. Investigation of concentration-response data by use of various analogues of ATP suggests the presence of an extracellular receptor which fails to fit into the current classification of purinoceptors. 4. Cross-desensitization experiments suggest that the same receptor can also be activated by the structurally different pyrimidine base, UTP. 5. Application of the tumour-promoting agent, beta-phorbol-12,13 dibutyrate (PDBu) caused a reduction in the increases in both [Ca2+]i and InsP3, suggesting a role for protein kinase C in feedback inhibition of purinoceptor responses in this cell line. 6. In summary, we present the first evidence for the existence of an atypical purinoceptor on a cell line of CNS origin. This receptor is linked to stimulation of phosphoinositide turnover and subsequent mobilisation of intracellular calcium.

Adenosine Triphosphate↗
PubMed1991

Do polyamines regulate the NMDA inhibition of muscarinic receptor-induced phosphoinositide turnover in guinea pig brain?

The N-methyl-D-aspartate (NMDA) receptor-induced inhibition of muscarinic receptor-stimulated phosphoinositide turnover in guinea pig cerebral cortical slices was investigated to determine whether polyamines regulate the function of NMDA in this system. None of the polyamines tested produced significant stimulation of phosphoinositide turnover. Neither spermine nor the substituted polyamine philanthotoxin-343 altered the inhibitory effect of NMDA. The simpler substituted polyamines N-(4-hydroxyphenylpropanoyl)-spermine and N-(4-hydroxyphenylacetyl)-spermine, however, antaganised the NMDA receptor inhibition of the muscarinic response with low affinity (Ki greater than or equal to 100 microM). Diethylenetriamine, a purported polyamine antagonist of the NMDA receptor, was without effect on the NMDA inhibitory response, as was ifenprodil, a structurally unrelated compound with reported antagonist capacity. In summary, therefore, we fail to observe polyamine regulation of the NMDA receptor mediating an inhibition of the muscarinic phosphoinositide turnover response in guinea pig cerebral cortical slices.

Animals↗
PubMed1991

Alpha- and beta-adrenoceptor regulation of cyclic AMP accumulation in cultured rat astrocytes. A comparison of primary protoplasmic and mixed fibrous/protoplasmic astroglial cultures.

The effect of noradrenaline and isoprenaline on cyclic AMP accumulation has been investigated in primary rat astrocytes which contain either (a) protoplasmic astrocytes alone or (b) both fibrous and protoplasmic astrocytes. Isoprenaline and noradrenaline stimulated cyclic AMP formation in both astrocyte culture preparations. Combinations of noradrenaline (1 microM) and isoprenaline (1 microM) produced a cyclic AMP response which was 58% and 26% of that produced by isoprenaline alone in protoplasmic and mixed fibrous/protoplasmic cultures, respectively. In both preparations this inhibitory effect of noradrenaline was antagonized by the alpha 2-adrenoceptor antagonist yohimbine (1 microM). A striking feature of the concentration-response curve for isoprenaline (EC50 = 0.8 microM) in mixed fibrous/protoplasmic cultures was that the cyclic AMP response decreased sharply at concentrations above 1 microM. This phenomenon was not seen in cultures containing protoplasmic astroglia alone. The fall in the isoprenaline concentration-response curve was not observed in the presence of the alpha-adrenoceptor antagonist phentolamine (1 microM), the dihydropyridine calcium antagonist isradipine (10 microM), the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (0.1 mM) or in nominally calcium-free medium. The effect of phentolamine was mimicked by the alpha 1-adrenoceptor antagonist prazosin (1 microM) but not by the alpha 2-antagonist yohimbine (1 microM). In conclusion, the data from this study suggest that two different populations of astrocytes in in vitro culture are able to raise intracellular cyclic AMP levels via beta-adrenoceptor activation and that there are differences in the extent of alpha-adrenoceptor (both alpha 1- and alpha 2-) mediated inhibition of cyclic AMP accumulation between the two primary astroglial cell preparations.

Adrenergic Antagonists↗
PubMed1991

Functional limits of conformation, hydrophobicity, and steric constraints in prokaryotic signal peptide cleavage regions. Wild type transport by a simple polymeric signal sequence.

These experiments examine the role of conformation, hydrophobicity, and steric constraints in the function of the prokaryotic signal peptide cleavage region. The experimental strategy involves replacement of the wild type Escherichia coli alkaline phosphatase signal peptide cleavage region with a series of idealized model sequences designed to epitomize the particular structural and physical variables under study. By analyzing model sequences whose conformations have been determined by physical studies, we have demonstrated that efficient transport does not depend on the structural preference of the cleavage region. Although previous studies based on Chou-Fasman analysis have suggested that the cleavage region forms a beta-turn which is required for transport, our results demonstrate that either a beta-turn- or alpha-helix-fostering sequence in the cleavage region functions indistinguishably from wild type. Furthermore, the presence of a proline residue between the core and cleavage region, although common in natural sequences, is not essential for export. Cleavage regions of varying hydrophobicities can support translocation across the inner membrane, but the placement of bulky residues at positions -1 and -3 upstream of the cleavage site abolishes processing and transport to the periplasm. By reducing the signal peptide to simplified, idealized segments, this study has identified a largely polymeric sequence, MKQST(L10)-(A6), that functions equivalently to the wild type alkaline phosphatase signal peptide. This work starts to provide a basis for the design of a universal prokaryotic signal peptide that incorporates all the critical physical and structural characteristics required for transport function.

Amino Acid Sequence↗
PubMed1990

Expression of beta 2-adrenoceptors mediating cyclic AMP accumulation in astroglial and neuronal cell lines derived from the rat CNS.

The effect of isoprenaline on cyclic AMP accumulation has been investigated in the rat neuronal cell line B50 and the rat astrocytoma cell line C6. Noradrenaline and isoprenaline stimulated cyclic AMP accumulation in both cell lines. Isoprenaline (0.5 microM; EC50 = 0.1 microM) produced a rapid (T1/2 = 1.3 min) increase in [3H]cyclic AMP accumulation in B50 cells while the response to isoprenaline (0.1 microM; EC50 = 0.01 microM) in C6 cells was somewhat slower (T1/2 = 7.5 min). The response to 0.5 microM isoprenaline was antagonized by both propranolol (IC50 = 8.4 +/- 1.6 nM; N = 3) and the beta 2-selective antagonist ICI 118551 (IC50 = 2.1 +/- 0.2 nM; N = 6). However, no attenuation of the response to isoprenaline (0.5 microM) was observed at concentrations of the beta 1-adrenoceptor antagonist atenolol up to 10 microM (N = 3). In contrast, in C6 cells, which have previously been shown to possess beta 1-adrenoceptors, atenolol inhibited isoprenaline-induced (0.1 microM) cyclic AMP accumulation (IC50 = 2.0 +/- 0.5 microM; N = 6). Furthermore, the beta 2-selective antagonist ICI 118551 was much less potent in the C6 cell line (IC50 = 0.2 +/- 0.05 microM; N = 3) than in the B50 cells. In conclusion, the present data suggest that isoprenaline mediates cyclic AMP accumulation in the neuronal cell line via activation of beta 2-adrenoceptors, while in the astrocytoma cell line the cyclic AMP response is mediated by beta 1-adrenoceptors.

Animals↗