Inhibition of duodenal enterocyte Mg2+-ATPase by arachidonic acid is not mediated by an effect on protein kinase C

Active absorption processes in the duodenal enterocyte are driven by various ATPases. It is known that the activity of Na+,K+-ATPase, Ca2+-ATPase and Mg2+-ATPase can be modulated by polyunsaturated fatty acids of the n-6 series, for example by linoleic and gamma-linolenic acids. These effects may be achieved by protein phosphorylation via protein kinase C. The present study was undertaken to determine the effect of arachidonic acid on Mg2+-ATPase (measured colorimetrically) activity in basolateral membranes prepared from rat duodenum. It shows, for the first time, significant dose-dependent inhibition of Mg2+-ATPase (26-62%) by arachidonic acid (10-50 microg/ml) which already takes place after one minute of exposure, indicating involvement of a rapid signal transduction mechanism. Addition of the protein kinase C inhibitors bisimidolylmaleimide (2.5 microM) and calphostin (0.5 microM) did not influence the action of arachidonic acid on Mg2+-ATPase; protein kinase C involvement in this process is thus not indicated.

[D-Trp(34)] neuropeptide Y is a potent and selective neuropeptide Y Y(5) receptor agonist with dramatic effects on food intake

The neuropeptide Y (NPY) Y(5) receptor has been proposed to mediate several physiological effects of NPY, including the potent orexigenic activity of the peptide. However, the lack of selective NPY Y(5) receptor ligands limits the characterization of the physiological roles of this receptor. Screening of several analogs of NPY revealed that [D-Trp(34)]NPY is a potent and selective NPY Y(5) receptor agonist. Unlike the prototype selective NPY Y(5) receptor agonist [D-Trp(32)]NPY, [D-Trp(34)]NPY markedly increases food intake in rats, an effect that is blocked by the selective NPY Y(5) receptor antagonist CGP 71683A. These data demonstrate that [D-Trp(34)]NPY is a useful tool for studies aimed at determining the physiological roles of the NPY Y(5) receptor.

Effects of selective protein kinase C inhibitors on the proteolytic down-regulation of L-selectin from chemoattractant-activated neutrophils

The signaling factors that direct the rapid shedding of L-selectin from neutrophils upon chemoattractant stimulation are poorly understood. Protein kinase C (PKC) has been implicated, yet previous studies have relied on the use of phorbol esters and nonselective kinase inhibitors. We treated neutrophils with various selective kinase inhibitors to evaluate their effects on N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced L-selectin shedding. We found that three selective inhibitors of PKC, structurally related to staurosporine, largely blocked both fMLP- and phorbol 12-myristate 13-acetate (PMA)-induced L-selectin shedding; however, these inhibitors did not affect fMLP-induced up-regulation of Mac-1 (CD11b/CD18) expression, which has been shown not to involve PKC. Other selective serine, threonine, and tyrosine kinase inhibitors were found not to block fMLP-induced L-selectin shedding. These findings provide more definitive evidence for the role of PKC in chemoattractant-induced L-selectin proteolysis. It is interesting that certain highly selective PKC inhibitors, not structurally related to staurosporine, were found to directly induce L-selectin shedding from neutrophils.

Differential effects of dopamine receptor subtype blockade on performance of rats in a reaction-time paradigm

RATIONALE

Pharmacological manipulation of the dopaminergic system with antipsychotic agents disrupts motor behavior. Although most antipsychotic drugs have high affinity for D2 receptors, they also interact with other dopamine receptor subtypes. Therefore, the role of each of these receptor subtypes on motor performance is unclear.

OBJECTIVE

The present study sought to investigate the relative importance of D1, D2, and D3 receptors on performance in a conditioned reaction-time task known to be extremely sensitive to dysfunction of the dopaminergic nigrostriatal pathway.

METHODS

Rats were trained to release a lever in response to a visual cue within a reaction-time limit to receive a reinforcer (45mg food pellet). After the behavior of the rats had stabilized, the effects of a D1 (A69024), D2 (eticlopride), and D3 (nafadotride) receptor antagonists were assessed.

RESULTS

A-69024 had no effect on performance at any dose tested (0.3, 0.6, and 1.3 mg/kg s.c.). Nafadotride (0.1, 0.3, and 1 mg/kg s.c.) produced only a mild deficit in performance at the highest dose. This deficit was characterized by an increase in the number of delayed responses with a non-significant decrease in the number of premature responses indicative of non-specific sedative effects. In contrast, the D2 receptor antagonist eticlopride (0.005, 0.01, and 0.02 mg/kg s.c.) produced profound deficits in performance as evidenced by a dose-dependent decrease in the number of correct responses. This decrease was accompanied by an increase in the number of delayed responses and a lengthening of the reaction time at the highest doses.

CONCLUSIONS

These results provide further evidence that the execution of the reaction-time task is dependent preferentially upon the activation of D2 receptors, but not D1 or D3 receptors.

Cannabinoid receptor modulation of synapses received by cerebellar Purkinje cells

The high density of cannabinoid receptors in the cerebellum and the degradation of motor coordination produced by cannabinoid intoxication suggest that synaptic transmission in the cerebellum may be strongly regulated by cannabinoid receptors. Therefore the effects of exogenous cannabinoids on synapses received by Purkinje cells were investigated in rat cerebellar slices. Parallel fiber-evoked (PF) excitatory postsynaptic currents (EPSCs) were strongly inhibited by bath application of the cannabinoid receptor agonist WIN 55212-2 (5 microM, 12% of baseline EPSC amplitude). This effect was completely blocked by the cannabinoid CB1 receptor antagonist SR 141716. It is unlikely that this was the result of alterations in axonal excitability because fiber volley velocity and kinetics were unchanged and a cannabinoid-induced decrease in fiber volley amplitude was very minor (93% of baseline). WIN 55212-2 had no effect on the amplitude or frequency of spontaneously occurring miniature EPSCs (mEPSCs), suggesting that the effect of CB1 receptor activation on PF EPSCs was presynaptically expressed, but giving no evidence for modulation of release processes after Ca(2+) influx. EPSCs evoked by climbing fiber (CF) stimulation were less powerfully attenuated by WIN 55212-2 (5 microM, 74% of baseline). Large, action potential-dependent, spontaneously occurring inhibitory postsynaptic currents (sIPSCs) were either severely reduced in amplitude (<25% of baseline) or eliminated. Miniature IPSCs (mIPSCs) were reduced in frequency (52% of baseline) but not in amplitude, demonstrating suppression of presynaptic vesicle release processes after Ca(2+) influx and suggesting an absence of postsynaptic modulation. The decrease in mIPSC frequency was not large enough to account for the decrease in sIPSC amplitude, suggesting that presynaptic voltage-gated channel modulation was also involved. Thus, while CB1 receptor activation reduced neurotransmitter release at all major classes of Purkinje cell synapses, this was not accomplished by a single molecular mechanism. At excitatory synapses, cannabinoid suppression of neurotransmitter release was mediated by modulation of voltage-gated channels in the presynaptic axon terminal. At inhibitory synapses, in addition to modulation of presynaptic voltage-gated channels, suppression of the downstream vesicle release machinery also played a large role.

Protein kinase-dependent phosphorylation and cannabinoid receptor modulation of potassium A current (IA) in cultured rat hippocampal neurons

The potent cannabinoid receptor agonist WIN 55,212-2 produces positive shifts in steady-state inactivation of the potassium A current (IA) in rat hippocampal neurons via an adenosine 3',5'-cyclic monophosphate (cAMP)-, protein kinase A (PKA)-dependent process. This effect is probably mediated by phosphorylation or dephosphorylation of the IA channel protein. The role of protein phosphorylation in this cascade was tested by testing cannabinoid actions in cultured hippocampal neurons (pyramidal cells) that were exposed also to either the catalytic subunit of PKA (PKAc), a PKA-specific phosphorylation inhibitor (IP-20, Walsh peptide), or a potent protein phosphatase inhibitor (okadaic acid). Cannabinoids such as WIN 55,212-2 produce a positive (rightwards) shift in the steady-state inactivation of IA, thus providing increased current at a given membrane voltage. Cells dialyzed with PKAc showed a negative shift in IA inactivation, opposite to that produced by cannabinoids, and similar to that produced by increased levels of cAMP. In addition, PKAc completely blocked the positive shift produced by WIN 55,212-2. In contrast, dialysis of cells with IP-20 produced a positive shift in steady state inactivation of IA, similar to that produced by WIN, but the effects were not additive with cannabinoid receptor activation. The phosphatase inhibitor, okadaic acid produced a small negative shift in IA steady-state inactivation when administered alone, and blocked the positive shift produced by WIN 55,212-2. Okadaic acid also enhanced the negative shift in IA inactivation when co-administered with forskolin. The effects of okadaic acid and WIN 55,212-2 were not additive, suggesting a common pathway. These results demonstrate that IA is altered by direct manipulations of the phosphorylation status of the channel protein, and that cannabinoid effects on IA are probably mediated by dephosphorylation of the IA channel.

Dopamine D3 receptor agents as potential new medications for drug addiction

All drugs abused by humans increase dopamine in the shell of nucleus accumbens, which implicate the neurons of this structure in their hedonic and reinforcing properties. Among the various dopamine receptor subtypes, the D(1) (D(1)R) and D(3) (D(3)R) receptors co-localise in accumbal shell neurons. Synergistic D(1)R/D(3)R interactions at this level were found on gene expression and during induction and expression of behavioral sensitisation to levodopa in rats bearing unilateral lesions of dopamine neurons. Behavioral sensitisation to abused drugs is a component of their long-term effects. Converging pharmacologic, human postmortem and genetic studies suggest the involvement of the D(3)R in reinforcing effects of drugs; D(3)R agonists reduced cocaine self-administration in rats, without disrupting the maintenance of self-administration. These data suggest the use of D(3)R agonists as partial substitutes to treat cocaine dependence, by affecting its reward component. However, substitution therapies maintain dependence and may be inefficient on drug craving and relapse, which are the unsolved and critical problems in the treatment of drug addiction. Recently, a highly selective and partial D(3)R agonist was shown to reduce cocaine-associated cue-controlled behaviour in rats, without having any primary intrinsic effects. As drug-associated cues maintain drug-seeking in animals and elicit craving and relapse in humans, such D(3)R agents have potential therapeutic applications.

Characterisation of human melatonin mt(1) and MT(2) receptors by CRE-luciferase reporter assay

A cyclic AMP response element (CRE)-luciferase reporter gene assay was used to characterise the functional responses of human melatonin mt(1) and human melatonin MT(2) receptors, stably expressed in the human embryonic kidney cell line HEK293, to a series of six naphthalenic analogues of melatonin. By comparison to the observed melatonin-mediated inhibition of stimulated luciferase levels the naphthalenic series was identified as comprising agonists, partial agonists and one antagonist of melatonin mt(1) and melatonin MT(2) receptor function. Three of the agonist/partial agonist members of this series were also identified as displaying a functional selectivity for the melatonin MT(2) receptor. Competitive displacement of 2-[125I]iodomelatonin binding to the ovine pars tuberalis melatonin ML(1) receptor demonstrated a close correlation to the observed functional luciferase responses of the human melatonin mt(1) receptor. We conclude that the CRE-luciferase reporter gene assay provides an effective functional screening method for the pharmacological characterisation of human melatonin receptor subtypes.

Sites of action of protein kinase C and phosphatidylinositol 3-kinase are distinct in oxidized low density lipoprotein-induced macrophage proliferation

Oxidized low density lipoprotein (Ox-LDL) can induce macrophage proliferation in vitro. To explore the mechanisms involved in this process, we reported that activation of protein kinase C (PKC) is involved in its signaling pathway (Matsumura, T., Sakai, M., Kobori, S., Biwa, T., Takemura, T., Matsuda, H., Hakamata, H., Horiuchi, S., and Shichiri, M. (1997) Arterioscler. Thromb. Vasc. Biol. 17, 3013-3020) and that expression of granulocyte/macrophage colony-stimulating factor (GM-CSF) and its subsequent release in the culture medium are important (Biwa, T., Hakamata, H., Sakai, M., Miyazaki, A., Suzuki, H., Kodama, T., Shichiri, M., and Horiuchi, S. (1998) J. Biol. Chem. 273, 28305-28313). However, a recent study also demonstrated the involvement of phosphatidylinositol 3-kinase (PI3K) in this process. In the present study, we investigated the role of PKC and PI3K in Ox-LDL-induced macrophage proliferation. Ox-LDL-induced macrophage proliferation was inhibited by 90% by a PKC inhibitor, calphostin C, and 50% by a PI3K inhibitor, wortmannin. Ox-LDL-induced expression of GM-CSF and its subsequent release were inhibited by calphostin C but not by wortmannin, whereas recombinant GM-CSF-induced macrophage proliferation was inhibited by wortmannin by 50% but not by calphostin C. Ox-LDL activated PI3K at two time points (10 min and 4 h), and the activation at the second but not first point was significantly inhibited by calphostin C and anti-GM-CSF antibody. Our results suggest that PKC plays a role upstream in the signaling pathway to GM-CSF induction, whereas PI3K is involved, at least in part, downstream in the signaling pathway after GM-CSF induction.

Effect of diabetes on bradykinin-induced thermal hyperalgesia in mice

To investigate the role of protein kinase C in the attenuation of bradykinin-induced thermal hyperalgesia in diabetic mice, we examined the effects of a protein kinase C activator or inhibitor on the i.t. bradykinin-induced hyperalgesia in diabetic and non-diabetic mice. Intrathecal injection of bradykinin caused a transient antinociceptive effect, which diminished within 30 min, and then produced a thermal hyperalgesia, which lasted about 120 min, in non-diabetic mice. Although the duration of the antinociceptive phase was longer in diabetic mice than in non-diabetic mice, the hyperalgesic response was not observed in diabetic mice. The bradykinin-induced hyperalgesia was dose-dependently and significantly enhanced by pretreatment with calphostin C (0.3 to 3 pmol, i.t.), a specific protein kinase C inhibitor, in diabetic mice. However, calphostin C (3 pmol, i.t.) had no significant effect on bradykinin-induced hyperalgesia in non-diabetic mice. On the other hand, pretreatment with phorbol-12, 13-dibutyrate (12.5 to 50 pmol, i.t.), a protein kinase C activator, significantly and dose-dependently reduced bradykinin-induced hyperalgesia in non-diabetic mice. However, phorbol-12, 13-dibutyrate (50 pmol, i.t. ) had no significant effect on bradykinin-induced hyperalgesia in diabetic mice. These results suggest that the change in bradykinin-induced thermal hyperalgesia in diabetic mice may be due, at least in part, to the modification of nociceptive transmission in the spinal cord by the activation of protein kinase C.

Protein kinase C targeting in antineoplastic treatment strategies

Neoplastic cell survival is governed by a balance between pro-apoptotic and anti-apoptotic signals. Noteworthy among several anti-apoptotic signaling elements is the protein kinase C (PKC) isoenzyme family, which mediates a central cytoprotective effect in the regulation of cell survival. Activation of PKC, and subsequent recruitment of numerous downstream elements such as the mitogen-activated protein kinase (MAPK) cascade, opposes initiation of the apoptotic cell death program by diverse cytotoxic stimuli. The understanding that the lethal actions of numerous antineoplastic agents are, in many instances, antagonized by cytoprotective signaling systems has been an important stimulus for the development of novel antineoplastic strategies. In this regard, inhibition of PKC, which has been shown to initiate apoptosis in a variety of malignant cell types, has recently been the focus of intense interest. Furthermore, there is accumulating evidence that selective targeting of PKC may prove useful in improving the therapeutic efficacy of established antineoplastic agents. Such chemosensitizing strategies can involve either (a) direct inhibition of PKC (e.g., following acute treatment with relatively specific inhibitors such as the synthetic sphingoid base analog safingol, or the novel staurosporine derivatives UCN-01 and CGP-41251) or (b) down-regulation (e.g., following chronic treatment with the non-tumor-promoting PKC activator bryostatin 1). In preclinical model systems, suppression of the cytoprotective function(s) of PKC potentiates the activity of cytotoxic agents (e.g., cytarabine) as well as ionizing radiation, and efforts to translate these findings into the clinical arena in humans are currently underway. Although the PKC-driven cytoprotective signaling systems affected by these treatments have not been definitively characterized, interference with PKC activity has been associated with loss of the mitogen-activated protein kinase (MAPK) response. Accordingly, recent pre-clinical studies have demonstrated that pharmacological disruption of the primary MEK-ERK module can mimic the chemopotentiating and radiopotentiating actions of PKC inhibition and/or down-regulation.

The anticataleptic effect of 7-OH-DPAT: are dopamine D3 receptors involved?

The paper examined the effect of 7-OH-DPAT (7-hydroxy-N,N-di-n-propyl-2-aminotetralin), a dopamine D3 receptors-prefering agonist, on the catalepsy evoked by reserpine, haloperidol and fluphenazine in rats (male Wistar), as well as the influence of nafadotride, a dopamine D3 receptors-prefering antagonist, on that effect. The obtained results show that 7-OH-DPAT, as well as L-DOPA, a drug of choice in the therapy of Parkinson's disease, used for comparison, antagonize the catalepsy induced by reserpine, haloperidol and fluphenazine. Nafadotride, used in a dose (0.2 mg/kg) which inhibits the 7-OH-DPAT-evoked locomotor hyperactivity but does not affect the hypermotility induced by amphetamine and quinpirole, antagonizes the anticataleptic effect of 7-OH-DPAT or L-DOPA. It is therefore assumed that dopamine D3 receptors are involved in the anticataleptic effect of both 7-OH-DPAT and L-DOPA.

Phospholipase A(2) is involved in thapsigargin-induced sodium influx in human lymphocytes

Previously, we reported that emptying of intracellular Ca(2+) pools with endoplasmatic Ca(2+)-ATP-ase inhibitor thapsigargin leads to the Na(+) influx in human lymphocytes (M. Tepel et al., 1994, J. Biol. Chem. 269, 26239-26242). In the present study we examined the mechanism underlying the thapsigargin-induced Na(+) entry. We found that the thapsigargin-induced increase in Na(+) concentration was effectively inhibited by three structurally unrelated phospholipase A(2) (PLA(2)) inhibitors, p-bromophenacyl bromide, 3-(4-octadecyl)-benzoylacrylic acid (OBAA), and bromoenol lactone (BEL). The thapsigargin-induced Na(+) influx could be mimicked by PLA(2) exogenously added to the lymphocyte suspension. In addition, thapsigargin stimulated formation of arachidonic acid (AA), the physiological PLA(2) product. AA induced Na(+) entry in a time- and concentration-dependent fashion. Both, thapsigargin-induced Na(+) influx and AA liberation were completely inhibited in the presence of tyrosine kinase inhibitor genistein but not in the absence of extracellular Ca(2+). Collectively, these data show that thapsigargin-induced Na(+) entry is associated with tyrosine kinase-dependent stimulation of PLA(2).

Ca(2+)-evoked serotonin secretion by parafollicular cells: roles in signal transduction of phosphatidylinositol 3'-kinase, and the gamma and zeta isoforms of protein kinase C

Parafollicular (PF) cells secrete 5-HT in response to stimulation of a G-protein-coupled Ca(2+) receptor (CaR) by increased extracellular Ca(2+) (upward arrow[Ca(2+)](e)). We tested the hypothesis that protein kinase C (PKC) participates in stimulus-secretion coupling. Immunoblots from membrane and cytosolic fractions of isolated PF cells revealed conventional (alpha, betaI, and gamma), novel (delta and epsilon), and atypical (iota/lambda and zeta) PKCs. Only PKCgamma was found to have been translocated to the membrane fraction when secretion of 5-HT was evoked by upward arrow[Ca(2+)](e) or phorbol esters. Although phorbol downregulation caused PKCgamma to disappear, secretion was only partially inhibited. A similar reduction of upward arrow[Ca(2+)](e)-evoked secretion was produced by inhibitors of conventional and/or novel PKCs (Gö 6976, calphostin C, and pseudoA), and these compounds did not inhibit secretion at all when applied to phorbol-downregulated cells. In contrast, the phorbol downregulation-resistant component of secretion was abolished by pseudoZ, which inhibits the atypical PKCzeta. Stimulation of PF cells with upward arrow[Ca(2+)](e) increased the activity of immunoprecipitated PKCzeta (but not PKCiota/lambda), and the activity of this PKCzeta was inhibited by pseudoZ. PF cells were found to express regulatory (p85) and catalytic (p110alpha and p110beta) subunits of phosphatidylinositol 3'-kinase (PI3'-kinase). upward arrow[Ca(2+)](e) increased the activity of immunoprecipitated PI3'-kinase; moreover, PI3'-kinase inhibitors (wortmannin and LY294002) antagonized secretion. We suggest that PKC isoforms mediate secretion of 5-HT by PF cells in response to stimulation of the CaR. PKC involvement can be accounted for by PKCgamma and an isoform sensitive to inhibition by pseudoZ, probably PKCzeta, which is activated via PI3'-kinase.

Isolation of a non-covalent aldose reductase-nucleotide-inhibitor complex

A method for the isolation of an intact, non-covalent complex formed by the interaction of aldose reductase, NADP(H) nucleotide, and inhibitor has been developed to aid in the discovery and development of novel aldose reductase inhibitors. In the complexes isolated, both the carboxylic acid-containing inhibitor tolrestat and the spirohydantoin-containing inhibitor AL1576 (2,7-difluorospirofluorene-9,5'-imidazolidine-2',4'-dione) tightly bound in a 1:1 ratio to aldose reductase complexed with either NADPH or NADP+. Inhibitor binding to either the enzyme-NADP+ or enzyme-NADPH complex appeared to be equal and pH-dependent, with maximum binding observed at a pH range of 7 to 8.5 where the inhibitors are ionized. These results indicated that the charge state of the cofactor (NADPH vs NADP+) is not critical for inhibitor binding to aldose reductase. Molecular modeling studies suggested that His110 plays a crucial role in directing charged inhibitors containing either a carboxylate or an ionizable hydantoin group to the active site of aldose reductase by providing charge interaction.

Chemical and enzymatic modifications of integric acid and HIV-1 integrase inhibitory activity

Integric acid (1), an acyl eremophilane sesquiterpenoid, was identified as an inhibitor of HIV-1 integrase, the enzyme responsible for provirus entry into the host cell nucleus and integration in to the host genome. Chemical and enzymatic modification of integric acid led to the preparation of several selective chemical derivatives of integric acid. Preparation, HIV-1 inhibitory activity, and the structure-activity relationship against coupled and strand transfer assays are described. It appears that most of the groups present in the natural product are required for inhibition of HIV-1 integrase strand transfer activity. In contrast, inhibition of 3' processing activity is less stringent suggesting distinct SAR for the two integrase reactions.

Interleukin-1beta inhibits gamma-aminobutyric acid type A (GABA(A)) receptor current in cultured hippocampal neurons

Interleukin-1beta (IL-1beta), a polypeptide immune mediator, is induced within the central nervous system in response to a variety of pathological stimuli, including systemic infection, hypoxia, brain trauma, and seizure. IL-1beta action on the gamma-aminobutyric acid type A (GABA(A)) inhibitory neurotransmitter receptor was investigated in whole cell patch-clamped cultured hippocampal neurons. Application of IL-1beta at concentrations encountered in pathophysiological conditions (1-10 ng/ml; 59-590 pM) irreversibly decreased the peak magnitude of current elicited by 30 microM GABA. Current inhibition was IL-1beta concentration- and time-dependent and was prevented by a specific IL-1beta type I receptor antagonist. No significant changes in current kinetics or reversal potential were observed. The IL-1beta depression of GABA current was inhibited by high concentrations of nonspecific kinase inhibitors staurosporine (500 nM) and 1-(5-isoquinolinyl-sulfonyl)-2-methylpiperazine (H-7; 50 microM), but not by a protein kinase C selective inhibitor calphostin C (5 microM). We conclude that IL-1beta inhibits GABA(A) receptor function in hippocampal neurons by the involvement of an unidentified kinase. This blockade of the GABA(A) inhibitory neurotransmitter receptor may underlie the central nervous system hyperexcitability seen in many pathophysiological conditions.

p38 MAP kinase is required for vasopressin-stimulated HSP27 induction in aortic smooth muscle cells

We previously showed that arginine vasopressin (AVP) stimulates heat shock protein 27 (HSP27) induction through protein kinase C activation in aortic smooth muscle A10 cells. In the present study, we examined whether the mitogen-activated protein (MAP) kinase superfamily is involved in the AVP-stimulated HSP27 induction in A10 cells. AVP stimulated the phosphorylation of p42/p44 MAP kinase and p38 MAP kinase. On the contrary, AVP had little effect on SAPK (stress-activated protein kinase)/JNK (c-Jun N-terminal kinase) phosphorylation. The HSP27 accumulation by AVP was not affected by PD98059, an inhibitor of the upstream kinase that activates p42/p44 MAP kinase. SB203580 and PD169316, specific inhibitors of p38 MAP kinase, suppressed the AVP-induced accumulation of HSP27. 12-O-tetradecanoylphorbol 13-acetate, an activator of protein kinase C, induced accumulation of HSP27 and was not inhibited by PD98059 but was inhibited by SB203580. Calphostin C and ET-18-OCH(3), inhibitors of protein kinase C, reduced the phosphorylation of p38 MAP kinase by AVP. SB203580 and PD169316 suppressed the AVP-increased levels in mRNA for HSP27. Dissociation of the aggregated HSP27 to the dissociated HSP27 was induced by AVP. These results strongly suggest that p38 MAP kinase takes part in the pathway of the AVP-stimulated induction of HSP27 in vascular smooth muscle cells.

Comparison of novel cannabinoid partial agonists and SR141716A in the guinea-pig small intestine

The controversial nature of the CB(1) receptor antagonist, SR141716A, in the guinea-pig small intestine was investigated by comparing it with four analogues of Delta(8)-tetrahydrocannabinol (Delta(8)-THC): O-1184, O-1238, O-584 and O-1315. These compounds (10 - 1000 nM) inhibited the electrically-evoked contractions with a rank order of potency of O-1238>O-1184>O-584>O-1315. Log concentration-response curves for O-1238, O-1184 and O-1315 were significantly shifted to the right by SR141716A and the maxima were significantly less than that of the CB(1) agonist, WIN55212-2, an indication of partial agonism. Partial saturation of the triple bond in O-1184 to a cis double bond (O-1238) increased its potency as an agonist (pEC(50) from 6.42 to 7.63) and as an antagonist of WIN55212-2, (pK(B), from 8.36 to 9.49). Substitution of the terminal azide group by an ethyl group (O-584) or removal of the phenolic hydroxyl group (O-1315) had no significant effect on the agonist or antagonist potency. None of these analogues increased the twitch response in a manner resembling that of SR141716A. O-1184 (10 and 100 nM) shifted the log concentration-response curve of WIN55212-2 for inhibition of the twitch responses to the right with pK(B) values of 8.29 and 8.38, respectively. We conclude that these Delta(8)-THC analogues behave as partial agonists rather than silent antagonists at CB(1) binding sites in this tissue. There was no evidence of antagonism of endocannabinoids thus supporting the hypothesis that, in this tissue, SR141716A is an inverse agonist of constitutively active CB(1) receptors.

Contribution of Are1p and Are2p to steryl ester synthesis in the yeast Saccharomyces cerevisiae

In the yeast Saccharomyces cerevisiae, two acyl-CoA:sterol acyltransferases (ASATs) that catalyze the synthesis of steryl esters have been identified, namely Are2p (Sat1p) and Are1p (Sat2p). Deletion of either ARE1 or ARE2 has no effect on cell viability, and are1are2 double mutants grow in a similar manner to wild-type despite the complete lack of cellular ASAT activity and steryl ester formation [Yang, H., Bard, M., Bruner, D. A., Gleeson, A., Deckelbaum, R. J., Aljinovic, G., Pohl, T. M., Rothstein, R. & Sturley, S. L. (1996) Science 272, 1353-1356; Yu, C., Kennedy, J., Chang, C. C. Y. & Rothblatt, J. A. (1996) J. Biol. Chem. 271, 24157-24163]. Here we show that both Are2p and Are1p reside in the endoplasmic reticulum as demonstrated by measuring ASAT activity in subcellular fractions of are1 and are2 deletion strains. This localization was confirmed by fluorescence microscopy using hybrid proteins of Are2p and Are1p fused to green fluorescent protein (GFP). Lipid analysis of are1 and are2 deletion strains revealed that Are2p and Are1p utilize sterol substrates in vivo with different efficiency; Are2p has a significant preference for ergosterol as a substrate, whereas Are1p esterifies sterol precursors, mainly lanosterol, as well as ergosterol. The specificity towards fatty acids is similar for both isoenzymes. The lack of steryl esters in are1are2 mutant cells is largely compensated by an increased level of free sterols. Nevertheless, terbinafine, an inhibitor of ergosterol biosynthesis, inhibits growth of are1are2 cells more efficiently than growth of wild-type. In a growth competition experiment are1are2 cells grow more slowly than wild-type after several rounds of cultivation, suggesting that Are1p and Are2p or steryl esters, the product formed by these two enzymes, are more important in the natural environment than under laboratory conditions.

In vitro interaction of terbinafine with itraconazole against clinical isolates of Scedosporium prolificans

In order to develop new approaches for the chemotherapy of invasive infections caused by Scedosporium prolificans, the in vitro interaction between itraconazole and terbinafine against 20 clinical isolates was studied using a checkerboard microdilution method. Itraconazole and terbinafine alone were inactive against most isolates, but the combination was synergistic against 95 and 85% of isolates after 48 and 72 h of incubation, respectively. Antagonism was not observed. The MICs obtained with the terbinafine-itraconazole combination were within levels that can be achieved in plasma.

Food intake regulation in rodents: Y5 or Y1 NPY receptors or both?

Neuropeptide Y (NPY), one of the most abundant peptides in rat and human brains, appears to act in the hypothalamus to stimulate feeding. It was first suggested that the NPY Y1 receptor (Y1R) was involved in feeding stimulated by NPY. More recently a novel NPY receptor subtype (Y5R) was identified in rat and human as the NPY feeding receptor subtype. There is, however, no absolute consensus since selective Y1R antagonists also antagonize NPY-induced hyperphagia. Nevertheless, new anti-obesity drugs may emerge from further pharmacological characterization of the NPY receptors and their antagonists. A large panel of Y1R and Y5R antagonists (such as CGP71683A, BIBO3304, BIBP3226, 1229U91, and SYNAPTIC and BANYU derivatives but also patentable in-house-synthesized compounds) have been evaluated through in vitro and in vivo tests in an attempt to establish a predictive relationship between the binding selectivity for human receptors, the potency in isolated organs assays, and the inhibitory effect on food intake in both normal and obese hyperphagic rodents. Although these results do not allow one to conclude on the implication of a single receptor subtype at the molecular level, this approach is crucial for the design of novel NPY receptor antagonists with potential use as anti-obesity drugs and for evaluation of their possible adverse peripheral side effects, such as hypotension.

Two populations of kainate receptors with separate signaling mechanisms in hippocampal interneurons

Consistent with the epileptogenic and deleterious effects of the potent neurotoxin kainate, the activation of kainate receptors reduces the synaptic inhibition induced by the amino acid gamma-aminobutyric acid (GABA). Extrapolating from these data led to the conclusion that kainate receptors are located presynaptically. However, kainate directly depolarizes the inhibitory interneurons, causing them to fire repeatedly. This effect might indirectly decrease the size of inhibitory postsynaptic currents recorded from pyramidal cells and places in doubt the presynaptic location for kainate receptors. Here we show that both effects, membrane depolarization and the reduction of inhibitory potentials, can be dissociated by several means, particularly by the natural agonist of kainate receptors, glutamate. Indeed, when applied at low concentrations, glutamate inhibited GABA release without affecting the firing rate of GABA interneurons. These results indicate that CA1 interneurons contain two populations of kainate receptors, each with different agonist sensitivity and coupled to distinct signaling pathways.

Regulation of LPA-promoted myofibroblast contraction: role of Rho, myosin light chain kinase, and myosin light chain phosphatase

Myofibroblasts generate the contractile force responsible for wound healing and pathological tissue contracture. In this paper the stress-relaxed collagen lattice model was used to study lysophosphatidic acid (LPA)-promoted myofibroblast contraction and the role of the small GTPase Rho and its downstream targets Rho kinase and myosin light chain phosphatase (MLCPPase) in regulating myofibroblast contraction. In addition, the regulation of myofibroblast contraction was compared with that of smooth muscle cells. LPA-promoted myofibroblast contraction was inhibited by the myosin light chain kinase (MLCK) inhibitors KT5926 and ML-7; however, in contrast to that observed in smooth muscle cells, elevation of intracellular calcium alone was not sufficient to promote myofibroblast contraction. These results suggest that Ca(2+)-mediated activation of MLCK, while necessary, is not sufficient to promote myofibroblast contraction. The specific Rho inactivator C3-transferase and the Rho kinase inhibitor Y-27632 inhibited LPA-promoted myofibroblast contraction, suggesting that contraction depends on activation of the Rho/Rho kinase pathway. Calyculin, a type 1 phosphatase inhibitor known to inhibit MLCPPase, could promote myofibroblast contraction in the absence of LPA, as well as restore contraction in the presence of C3-transferase or Y-27632. Together these results support a model whereby Rho/Rho kinase-mediated inhibition of MLCPPase is necessary for LPA-promoted myofibroblast contraction, in contrast to smooth muscle cells in which Ca(2+) activation of MLCK alone is sufficient to promote contraction.

Endothelin-1 (ET-1)-potentiated insulin secretion: involvement of protein kinase C and the ET(A) receptor subtype

Endothelin-1 (ET-1), a potent vasoconstrictor peptide of endothelial origin, is capable of influencing hormone secretion from endocrine tissues, eg, pancreatic islet cells. We have shown a direct stimulatory effect of ET-1 on insulin secretion from isolated mouse islets of Langerhans. However, it is unknown as to whether the peptide acts through specific receptors on the islet cells and which mechanisms are involved in this insulinotropic action. We have therefore used the specific ET(A) receptor antagonist BQ123, the ET(B) receptor agonist BQ3020, and classic alpha- and beta-adrenergic and cholinergic antagonists. ET-1 (100 nmol/L) stimulated insulin secretion from islets incubated at 8.3, 11.1, 16.7, and 25 mmol/L glucose (P < .05). At 3.3 mmol/L glucose, no alteration in insulin secretion was found. The cholinergic receptor antagonist atropine (5 micromol/L) or the adrenergic receptor antagonists propranolol (5 micromol/L) or phentolamine (5 micromol/L) did not affect ET-1 (100 nmol/L)-stimulated insulin secretion. BQ123 (10 pmol/L to 10 nmol/L) and BQ3020 (1 nmol/L to 1 micromol/L) had no effect on glucose (16.7 mmol/L)-stimulated insulin secretion, but BQ123 counteracted the stimulatory effect of ET-1 (100 nmol/L) at concentrations of 1 nmol/L to 10 micromol/L (P < .01). We also studied the relative role of protein kinase C (PKC) and a Wortmannin-sensitive pathway for ET-1-induced insulin secretion using 12-O-tetradecanoyl phorbol-13-acetate (TPA), Calphostin C, and Wortmannin, respectively. At 5.6 mmol/L glucose, ET-1 (100 nmol/L) had no effect per se, whereas in the presence of 1 micromol/L TPA, which acutely stimulates PKC, the peptide did potentiate insulin secretion (P < .05). Furthermore, the insulinotropic effect of ET-1 at 16.7 mmol/L glucose was counteracted by the PKC inhibitor Calphostin C (P < .05) and by downregulation of PKC by 24 hours of exposure of islets to TPA (0.5 micromol/L, P < .05). Wortmannin (1 micromol/L) did not alter ET-1-potentiated insulin secretion. In conclusion, our results suggest that ET-1 acts through specific ET-1 receptors, most likely the ETA subtype. Furthermore, PKC plays an essential role in the insulinotropic action of ET-1 in mouse islets.