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D J Nelson

Publications and source records attributed to D J Nelson.

At least 91 records · Page 5Linked to original sources
PubMed1992

Alternate pathways for chloride conductance activation in normal and cystic fibrosis airway epithelial cells.

Using whole cell patch-clamp and perforated patch recording techniques on human cystic fibrosis (CF) and non-CF airway epithelial cells, we sought to determine whether a single Cl- conductance (GCl) could be modulated via different regulatory pathways or whether multiple conductances could be identified. Cl- current in both CF and non-CF cells was activated by cellular swelling as well as by an elevation in intracellular calcium ([Ca2+]i). While the adenosine 3',5'-cyclic monophosphate (cAMP)-activated GCl was absent in CF cells, its activation in non-CF cells was only observed in the perforated patch configuration at lower temperatures (24 degrees C) or infrequently in the whole cell configuration at elevated temperatures (33 degrees C). Currents activated by all three regulatory pathways were sensitive to the Cl- channel blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). Further increases in current activation could be produced by cellular swelling after maximal Ca2+ or cAMP-induced current activation. Intracellular application of a peptide inhibitor of Ca(2+)-calmodulin-dependent protein kinase selectively blocked the Ca(2+)-dependent current activation while leaving the swelling-induced current increase intact. These results are consistent with the presence of multiple anion conductances in both CF and non-CF airway cells. The heterogeneity of the responses to the three regulatory stimuli, however, prevented the correlation of a specific anion conductance with a separate modulatory pathway based on characteristic voltage-dependent kinetics and conductance.

Calcium↗
PubMed1991

Antiprotozoal activity of 3'-deoxyinosine. Inverse correlation to cleavage of the glycosidic bond.

Two nucleosides related to the known antiprotozoal agent 1-(beta-D-ribofuranosyl)-1,5-dihydro-4H-pyrazolo-[3,4-d]pyrimidine-4-one (allopurinol riboside, 1) were prepared and evaluated against Leishmania donovani, Trypanosoma cruzi, and Trypanosoma gambiense. 3'-Deoxyinosine (2) exhibited potent antiprotozoal activity against the three protozoal pathogens with minimal toxicity for host cells. It was found to be especially effective against the Columbia strain of T. cruzi reported to be resistant to 1. The antiprotozoal activity of 2 appeared to be inversely related to the rate of cleavage of the glycosidic bond, as shown by metabolic profiles of 2 in the various pathogenic hemoflagellates and host cells. Combining the key structural elements of 1 and 2 led to the synthesis of 1-(3-deoxy-beta-D-erythro-pentofuranosyl)-1,5-dihydro-4H-pyrazolo[3,4-d] pyrimidin-4-one (3'-deoxy-allopurinol riboside, 3). which was found to be inactive as an antiprotozoal agent.

Animals↗
PubMed1991

Sequence and functional expression in Xenopus oocytes of a human insulinoma and islet potassium channel.

Regulation of insulin secretion involves the coordinated control of ion channels in the beta-cell membrane. We have isolated and characterized cDNA and genomic clones encoding a voltage-dependent K+ channel isoform expressed in human islets and in a human insulinoma. This K+ channel isoform, designated hPCN1, with a deduced amino acid sequence of 613 residues (Mr = 67,097), is related to the Shaker family of Drosophila K+ channels. hPCN1 is homologous to two other human K+ channel isoforms we have isolated, hPCN2 and hPCN3, with 55% and 65% amino acid sequence identity, respectively. The electrophysiological characteristics of hPCN1 were determined after microinjection of synthetic RNA into Xenopus oocytes. Two-microelectrode voltage-clamp recordings of oocytes injected with hPCN1 RNA revealed a voltage-dependent outward K+ current that inactivated slowly with time. Outward currents were inhibited by 4-aminopyridine with a Ki less than 0.10 mM and were relatively insensitive to tetraethylammonium ion or Ba2+. A delayed rectifier K+ channel such as hPCN1 could restore the resting membrane potential of beta cells after depolarization and thereby contribute to the regulation of insulin secretion.

Amino Acid Sequence↗
PubMed1991

Tumor necrosis factor inhibits K+ current expression in cultured oligodendrocytes.

The effects of tumor necrosis factor-alpha (TNF-alpha), a cytokine secreted by activated macrophages, on the electrical membrane properties of cultured adult ovine oligodendrocytes (OLGs) were investigated using the whole-cell voltage-clamp technique. Treatment with recombinant human TNF-alpha (rhTNF) for 24 to 72 hr produces (i) process retraction in some but not all OLGs, (ii) a reduction in the resting membrane potential with no significant change in membrane capacitance or input resistance over control cells and (iii) a decrease in the expression of both the inwardly rectifying and outward K+ current. The magnitude of the membrane potential change as well as K+ current inhibition was larger in cells with retracted processes. The electrophysiological effects of rhTNF were attenuated when rhTNF was neutralized with a polyclonal anti-rhTNF antibody. The binding of rhTNF to its receptor has been reported to increase GTP binding, to increase GTPase activity of a pertussis-sensitive G protein, and to produce an elevation in intracellular cAMP in other cell types. However, pretreatment of OLGs with activated pertussis toxin failed to attenuate or mimic the effects of rhTNF. Chronic exposure of OLGs to the membrane permeant analogue of cAMP, 8-bromo-cAMP, resulted primarily in an inhibition of the inwardly rectifying K+ current, an effect which was less than that produced by rhTNF alone and without any of the associated rhTNF-induced morphological changes. This indicates that the effects of rhTNF cannot be entirely accounted for by an elevation in intracellular cAMP. Cycloheximide (CHX), an inhibitor of protein synthesis, mimicked the effects of rhTNF; however, the effects of rhTNF and CHX were not additive. The finding that both ionic current expression and membrane potential were reduced in cells treated with rhTNF that appeared morphologically normal suggests that abnormal ion channel expression in OLGs precedes and may contribute to eventual myelin swelling and damage.

Animals↗
PubMed1991

Al3+ versus Ca2+ ion binding to methionine and tyrosine spin-labeled bovine brain calmodulin.

Bovine calmodulin analogues, spin-labeled at either methionine or tyrosine residues, have been utilized in electron paramagnetic resonance (EPR) studies to investigate possible calmodulin interactions with aluminum ion. The study attempts to clarify a previous report in the literature (H. Siegel, R. Coughlin, and A. Haug, Biochem. Biophys. Res. Commun. 115, 512 (1983)) which indicated, on the basis of EPR experiments on methionine spin-labeled protein, significant interaction between calmodulin and aluminum ion at pH = 6.5. In EPR metal ion titration experiments we have found that the signal line-shape (from both methionine and tyrosine spin labels) changed dramatically with the addition of calcium ion, but was virtually unchanged with the addition of aluminum ion at pH = 6.5. Experiments performed at pH = 5.5, where significantly more "free" aluminum ion (i.e., Al(H2O)6(3+) = Al3+) is present, also failed to produce the line-narrowing effect observed in the earlier study. Based on our EPR experiments, in the pH range 5.5 to 6.5, we find no evidence for significant interaction between calmodulin and aluminum ion.

Aluminum↗
PubMed1991

Pharmacokinetics and metabolism of allopurinol riboside.

There are no safe and effective oral drugs to treat leishmaniasis and Chagas' disease. The safety, pharmacokinetics, and metabolism of single and multiple oral doses of allopurinol riboside, an investigational antiparasitic agent, were evaluated in a randomized, double-blinded, placebo-controlled study in 32 healthy male volunteers, at levels up to 25 mg/kg q.i.d. for 13 doses. No significant toxicity was detected. Allopurinol riboside peaks in plasma 1.6 hours after administration, has an elimination half-life of 3 hours, and steady-state concentrations in the therapeutic range. However, in contrast to preclinical studies in dogs (plasma levels proportional to oral doses up to 200 mg/kg), we found that plasma levels were unexpectedly low and did not rise with increasing dose. Furthermore, allopurinol and oxypurinol (unanticipated metabolites) were detected at levels proportional to the dose of allopurinol riboside. We present a model that includes incomplete absorption, metabolism of residual drug by enteric flora, and absorption of bacterial metabolites to explain these findings in humans.

Adolescent↗
PubMed1990

Channel-mediated and carrier-mediated uptake of K+ into cultured ovine oligodendrocytes.

Uptake of radioactive K+ by mature ovine oligodendrocytes (OLGs) maintained in primary culture was measured under steady-state conditions, i.e., in cells maintained in a normal tissue culture medium (5.4 mM K+), and in cells after depletion of intracellular K+ to less than 15% of its normal value by pre-incubation in K(+)-free medium. The latter value is dominated by an active, carrier-mediated uptake (although it may include some diffusional uptake), whereas the former, in addition to active uptake, also reflects passive K+ diffusion through ion selective channels and possible self-exchange between extracellular and intracellular K+, which may be carrier-mediated. The total uptake rate was 144 +/- 10 nmol/min/mg protein, and the uptake after K+ depletion was 60 +/- 2 nmol/min/mg protein, much lower rates than previously observed in astrocytes. The uptake into K(+)-depleted cells was inhibited by about 80% in the presence of ouabain (1 mM) and about 30% in the presence of furosemide (2 mM). Activators of protein kinase C (phorbol esters) and cAMP-dependent protein kinase (forskolin) have been shown to alter the myelinogenic metabolism as well as outward K+ current in cultured OLGs. The present study demonstrates that K+ homeostasis in OLGs is modulated through similar second messenger pathways. Active uptake was inhibited by about 60% in the presence of active phorbol esters (100 nM) but was not affected by forskolin (100 nM). Forskolin likewise had no effect on total uptake, whereas phorbol esters caused a much larger inhibition than expected from their effect on carrier-mediated uptake alone, suggesting that channel-mediated uptake was also reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Beta-adrenergic modulation of K+ current in human T lymphocytes.

The whole-cell voltage-clamp technique was employed to study the beta-adrenergic modulation of voltage-gated K+ currents in CD8+ human peripheral blood lymphocytes. The beta-receptor agonist, isoproterenol, decreased the peak current amplitude and increased the rate of inactivation of the delayed rectifier K+ current. In addition, isoproterenol decreased the voltage dependence of steady-state inactivation and shifted the steady-state inactivation curve to the left. Isoproterenol, on the other hand, had no significant effect on the steady-state parameters of current activation. The isoproterenol-induced decrease in peak current amplitude was inhibited by the beta-blocker propranolol. Bath application of dibutyryl cAMP (1 mM) mimicked the effects of isoproterenol on both K+ current amplitude and time course of inactivation. Furthermore, the reduction in the peak current amplitude in response to isoproterenol was attenuated when PKI5-24 (2-5 microM), a synthetic peptide inhibitor of cAMP-dependent protein kinase, was present in the pipette solution. The increase in the rate of inactivation of the K+ currents in response to isoproterenol was mimicked by the internal application of GTP-gamma-S (300 microM) and by exposure of the cell to cholera toxin (1 microgram/ml), suggesting the involvement of a G protein. These results demonstrate that the voltage-dependent K+ conductance in T lymphocytes can be modulated by beta-adrenergic stimulation. The effects of beta-agonists, i.e., isoproterenol, appear to be receptor mediated and could involve cAMP-dependent protein kinase as well as G proteins. Since inhibition of the delayed rectifier K+ current has been found to decrease the proliferative response in T lymphocytes, the beta-adrenergic modulation of K+ current may well serve as a feedback control mechanism limiting the extent of cellular proliferation.

Cyclic AMP↗
PubMed1990

Whole-cell currents in macrophages: I. Human monocyte-derived macrophages.

We examined the variability of occurrence and frequency of voltage-dependent whole-cell currents in human peripheral blood monocyte-derived macrophages (HMDM) maintained in culture for up to three weeks. An increase in cell capacitance from an average value of 9 pF on the day of isolation to 117 pF at 14 days accompanied growth and differentiation in culture. The average resting potential was approximately -34 mV for cells beyond two days in culture. Cells exhibited a voltage- and time-dependent outward current upon membrane depolarization above approximately -30 mV, which appeared to be composed of a number of separate currents with variable expression from donor to donor. Three of these currents are carried by K+. The frequency of each outward current type was calculated for 974 cells obtained from 36 donors. The HMDMs in these studies exhibited two 4-aminopyridine (4-AP) sensitive, time-dependent outward currents (IA and IB) that could be differentiated on the basis of the presence or absence of steady-state inactivation in the physiological potential range, time course of inactivation during maintained depolarization, as well as threshold of activation. The 4-AP-insensitive outward current activated at approximately 10 mV. One component of the 4-AP insensitive-outward current (IC) could be blocked by external TEA and by the exchange of internal CS+ or Na+ for K+. The probability of observing IB and IC appeared to be donor dependent. Following total replacement of internal K+ with CS+, two additional currents could be identified (i) a delayed component of outward current (ID) remained which could be blocked by low concentrations of external Zn2+ (4 microM) and was insensitive to anion replacement in the external solution and (ii) a Cl- current with a reversal potential which shifted in the presence of external anion replacement and which was irreversibly inhibited by the stilbene SITS. The activation of a prominent time-independent inward current was often observed with increasing hyperpolarization. This inward current was blocked by external Ba2+ and corresponded to the inwardly rectifying K+ current. Neither inward nor outward current expression appeared dependent on whether cells were differentiated in adherent or suspension culture nor was there demonstrable differential current expression observed upon transition from suspension to adherent form.

4-Aminopyridine↗
PubMed1990

Whole-cell currents in macrophages: II. Alveolar macrophages.

Although an outwardly rectifying K+ conductance has been described in murine peritoneal macrophages and a murine macrophage cell line, the expression of this conductance in human monocyte-derived macrophages (HMDMs) is rare. Whole-cell current recordings in this study were obtained from HMDMs differentiated in adherent culture for varying periods of time following isolation and compared to currents obtained in human alveolar macrophages (HAMs) obtained from bronchoalveolar lavage. These studies were undertaken to compare ionic current expression in the in vitro differentiated macrophage to that of a human tissue macrophage. HAMs are the major population of immune and inflammatory cells in the normal lung and are the most readily available source of human tissue macrophages. Of the 974 HMDMs in the study obtained from a total of 36 donors, we were able to observe the presence of the inactivating outward current (IA) which exhibited voltage-dependent availability in only 49 (or 5%) of the cells. In contrast, whole-cell current recordings from HAMs, revealed a significantly higher frequency of IA expression (50% in a total of 160 cells from 26 donors). In the alveolar cell, there was no correlation observed between cell size and peak IA amplitude, nor was there a relationship between peak IA amplitude and time in culture. The current in both cell types was K+ selective and 4-aminopyridine (4-AP) sensitive. IA in both cell types inactivated with a time course which was weakly voltage-dependent and which exhibited a time constant of recovery from inactivation of approximately 30 sec. The time course of current inactivation was dependent upon the external K+ concentration. An increase in the time constant describing current decay was observed in elevated K+. Current activation was half-maximal at approximately -18 mV in normal bathing solution. Steady-state inactivation was half-maximal at approximately -44 mV. The presence of the outwardly rectifying K+ conductance may alter the potential of the mononuclear phagocyte to respond to extracellular signals mediating chemotaxis, phagocytosis, and tumoricidal functions.

4-Aminopyridine↗
PubMed1990

Comparison of Ca(II), Cd(II), and Mg(II) titrations of tyrosine-99 spin-labeled bovine calmodulin.

Bovine calmodulin, spin-labeled at tyrosine-99, has been utilized in electron paramagnetic resonance (EPR) studies to investigate calmodulin interactions with Ca(II), Cd(II), and Mg(II). The addition of either Ca(II) or Cd(II) to apo-calmodulin results in a complex capable of activating target enzymes, such as 3', 5'-cyclic nucleotide phosphodiesterase (J. M. Buccigross, C. L. O'Donnell, and D. J. Nelson, Biochem. J. 235 677 [1986]), while Mg(II) is known to be incapable of activating calmodulin toward any of its target enzymes. Additions of Ca(II) and Cd(II) to spin-labeled apo-calmodulin gave rise to very similar changes in the EPR spectrum of the bound label, consistent with a dramatic decrease in the mobility of the nitroxide spin-label covalently attached to tyrosine-99. Addition of Mg(II) to spin-labeled apo-calmodulin caused no change in the EPR spectrum of the bound label. Thus, the conformational changes induced by Ca(II) and Cd(II) ion binding to calmodulin, which lead to decreased tyrosine-99 spin label mobility, are clearly not occurring when Mg(II) ion binds. These results are consistent with the results of other spectroscopic studies, which indicate that "activating" metal ions, such as Ca(II) and Cd(II), produce calmodulin conformers that are different from those produced by "inactivating" metal ions, such as Mg(II).

Animals↗
PubMed1989

Inhibition of xanthine oxidase by 4-hydroxy-6-mercaptopyrazolo[3,4-d]pyrimidine.

Compound B103U, 4-hydroxy-6-mercaptopyrazolo[3,4-d]pyrimidine, was investigated as an inhibitor of human xanthine oxidase. Studies in vitro demonstrated that it was significantly more potent than oxypurinol, 4,6-dihydroxypyrazolo[3,4-d]pyrimidine. It formed an initial complex with electron-rich (reduced) human xanthine oxidase that was tighter than the corresponding complex formed by oxypurinol. The initial complexes with each inhibitor and reduced enzyme were internally rearranged into more stable complexes with first-order rate constants of 2.5 to 3 per min. However, the half-life of the isomerized (stable) complex with B103U was three to four times longer than the half-life of the analogous complex with oxypurinol. This stability was previously noted by Massey et al. (J. Biol Chem 254: 2837-2844, 1970) with B103U and bovine xanthine oxidase. The overall Ki values accounting for the initial and isomerized complexes were 5 nM for B103U and 100 nM for oxypurinol. B103U was also more potent as an inhibitor of bovine xanthine oxidase-catalyzed generation of superoxide radicals. Studies in mice revealed that the relative in vitro potency of B103U was not sustained in vivo. Compared to the inhibition of xanthine oxidase by oxypurinol, inhibition by B103U was neither more potent nor longer lasting. This shortcoming was not caused by weaker inhibition of mouse xanthine oxidase. Instead, it was the result of poor bioavailability. Plasma levels of available B103U rapidly decreased from samples of mouse and human blood because of reversible binding to serum proteins. B103U was also susceptible to oxidation. Two equivalents of H2O2 stoichiometrically oxidized the 6-thiol substituent to a sulfinic acid. This oxidized product was three orders of magnitude weaker as an inhibitor of xanthine oxidase than was B103U.

Animals↗
PubMed1989

Safety and efficacy of isradipine, alone and in combination, in the treatment of angina pectoris.

Five hundred ninety outpatients aged 18 years or older with stable angina pectoris entered a multicenter, single-blind, nonrandomized, baseline-controlled study to assess the efficacy, safety, and tolerability of isradipine in doses of 2.5, 5, or 7.5 mg three times daily for 12 weeks, following a two-week placebo "washout" period. Patients were assessed at the initial visit and, thereafter, every two weeks with a final evaluation at Week 14. The final mean dose was 5.9 mg three times daily. Overall, isradipine was found to reduce significantly the angina attack rate and nitroglycerin consumption in patients with chronic, stable, effort-induced angina pectoris. Isradipine was generally well tolerated when prescribed alone or with concomitant beta-blocker medication.

Adrenergic beta-Antagonists↗
PubMed1989

Solvent dependency of rotational barriers in ethamivan and comparison to nikethamide.

Carbon-13 nuclear magnetic resonance (NMR) techniques were employed to examine the effects of solvent environment on rotational barriers in two drugs known to cause widespread stimulation in the mammalian central nervous system: ethamivan and nikethamide. Total NMR bandshape analysis was performed for the exchanging alkyl carbon resonances of these compounds as a function of temperature in six solvent systems: D2O, CH3OD, CH3CH2OD, CDCl3, C6D6 and CF3CH2OH. The rate constants for rotation about the amide bond obtained in this way were used to calculate free energy (delta G++), enthalpy (delta H++) and entropy (delta S++) of activation parameters for this process. Our results indicate that the magnitude of rotational barriers is affected markedly by (1) the size and polarity of the solvent molecules, and (2) the nature of the aromatic ring system attached to the amide grouping. Comparative interpretation of the thermodynamic parameters in light of the structures of nikethamide and ethamivan (in the various solvent systems examined) has further clarified the manner in which hydrogen bonding interactions between solvent molecules and the carbonyl oxygen of these analogues stabilize transition state conformers.

Acetonitriles↗
PubMed1989

Phosphorylation of myelin basic protein in intact oligodendrocytes: inhibition by galactosylsphingosine and cyclic AMP.

We have previously shown that cyclic AMP (cAMP) inhibits the protein kinase C (PKC)-mediated phosphorylation of myelin basic protein (MBP) in cultured oligodendrocytes (OLGs). Recently, it has been demonstrated that the long chain base sphingosine inhibits PKC by competing PKC effectors (diacylglycerol and phorbol esters) for a binding site on the kinase (Hannun and Bell: Science 235: 670-674, 1987). In this report we define further the mechanism by which cAMP inhibits MBP phosphorylation by comparing the effects of cAMP with that of galactosylsphingosine (psychosine), a potential catabolite of galactocerebroside, the major OLG glycosphingolipid. We identify the consequences of psychosine treatment and PKC down-regulation on OLG morphology and electrophysiology and discuss their relevance. Our results in intact ovine oligodendrocytes are consistent with a mechanism in which cAMP inhibits MBP phosphorylation by interfering with the release of diacylglycerol (DAG) from phosphatidylinositol. First, the effects of cAMP on MBP phosphorylation are reversed with exogenous TPA; and second, cAMP inhibits the incorporation of 1-[14C]arachidonate into DAG and specifically inhibits the turnover (as judged by 32PO4 3-incorporation) of phosphatidylinositol. Psychosine inhibits MBP phosphorylation, and its action can be reversed by TPA suggesting a mechanism of inhibition similar to that described for other systems. In addition, psychosine has profound effects on OLG morphology; it disintegrates OLG processes while leaving the cell soma intact. Stable hyperpolarized resting potentials were obtained following psychosine treatment, but there was a 66% decrease in membrane capacitance indicating a significant decrement in membrane surface area. The morphological changes induced by psychosine are reversible and can be eliminated by removing the drug but not by the addition of TPA. Whether inhibition of PKC by psychosine plays any role in process dissolution remains an unanswered question. However, current evidence suggests that a PKC-independent mechanism may be at play. This investigation in conjunction with our previous work emphasizes a role for the interregulation of protein kinase A (PKA) and PKC in the control of OLG somal vs. myelin components. This may have significant implications for central nervous system myelin assembly.

Animals↗
PubMed1989

Voltage-gated chloride currents in cultured canine tracheal epithelial cells.

Chloride ions (Cl-) are concentrated in airway epithelial cells and subsequently secreted into the tracheal lumen by downhill flux through apical Cl- channels. We have studied Cl- currents in cultured canine tracheal cells using the whole-cell voltage-clamp technique. Ultrastructural techniques demonstrated that the cells used in the electrophysiological experiments possessed apical membrane specializations known to be present in the intact, transporting cell type. Cultured cells 2-6 days old were characterized by an input resistance of 3.4 +/- 0.8 G omega (n = 11) and a capacitance of 63.8 +/- 10.8 pF (n = 26). A comparison of 3 and 4 day-old cells with 5 and 6 day-old cells showed that the input resistance decreased almost 50%, and the cell capacitance and the inward and outward currents increased concomitantly approximately 200%. Cultured cells 3-4 days old held at -40 mV produced currents of 196 +/- 22 pA at 50 mV and -246 +/- 27 pA at -90 mV (n = 212) with pipette and bath solutions containing primarily 140 KCl and 140 NaCl, respectively. The chloride channel blocker diphenylamine-2-carboxylate (DPC, 100 microM) suppressed whole-cell currents by 76.8% at 60 mV; however, currents were unaffected by the stilbenes SITS (1 mM) and DNDS (1-30 microM). Replacement of K+ with Cs+ in the pipette solution did not affect the outward current, the current reversal potential, or the input resistance of the cells, indicating that the current was not significantly K+ dependent when the intrapipette solution was buffered to a Ca2+ concentration of 20 nM. The Cl-/Na+ permeability ratio was estimated to be greater than 11 as calculated from reversal potential measurements in the presence of an internal to external NaCl concentration ratio of 1:2. Current equilibrium permeabilities, relative to Cl- were: I- (2.9) much greater than NO3- (1.1) greater than or equal to Br- (1.1) greater than or equal to Cl- (1.0) greater than or equal to F- (0.93) much greater than MeSO4- (0.19) greater than or equal to gluconate (0.18) greater than or equal to aspartate (0.14). Depolarizations to potentials greater than 20 mV elicited a time-dependent component in the outward current in 71% of the cells studied. Currents inactivated with a double exponential time course at the most depolarized voltages. Recovery from inactivation was fast, holding potential-dependent, and followed a double exponential time course.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

2-Acetylpyridine 5-[(dimethylamino)thiocarbonyl]-thiocarbonohydrazone (A1110U), a potent inactivator of ribonucleotide reductases of herpes simplex and varicella-zoster viruses and a potentiator of acyclovir.

2-Acetylpyridine 5-[(dimethylamino)thiocarbonyl]thiocarbonohydrazone (A1110U) was found to be a potent inactivator of the ribonucleotide reductases (EC 1.17.4.1) encoded by herpes simplex virus types 1 and 2 and by varicella-zoster virus and to be a weaker inactivator of human ribonucleotide reductase. It also markedly potentiated the antiherpetic activity of acyclovir against these viruses in tissue culture. A1110U both decreased the dGTP pool that builds up when infected cells are treated with acyclovir and induced a large increase in the pool of acyclovir triphosphate. The resultant 100-fold increase in the ratio of the concentrations of acyclovir triphosphate to dGTP should facilitate the binding of the fraudulent nucleotide to its target enzyme, herpes virus-encoded DNA polymerase, and could account for the synergy between A1110U and acyclovir. A similar change in the acyclovir triphosphate-to-dGTP ratio was previously reported to be induced by another ribonucleotide reductase inhibitor, 2-acetylpyridine 4-(2-morpholinoethyl)thiosemicarbazone (A723U). However, A1110U is considerably more potent and may have better clinical potential. Synergistic toxic interactions between A1110U and acyclovir were not detected in uninfected cells.

Acyclovir↗