Forskolin interaction with voltage-dependent K channels in Helix is not mediated by cyclic nucleotides

The effects of the adenylate cyclase activator forskolin upon voltage-activated K(V) currents were investigated in Helix nerve cells. Forskolin induced a fast concentration-dependent inactivation of K(V) currents without modifying the activation kinetics. The induced fast inactivation did not result from a speeding up of the voltage-controlled slow inactivation; it could not be mimicked by intracellular injection of cAMP and it was not potentiated by inhibition of the phosphodiesterase. The forskolin induced K current relaxation can be simulated by a model assuming that the drug binds reversibly to open K channels with a dissociation constant of 16.4 microM.

A study of cyclic nucleotides as second messengers after interleukin 2 stimulation of human T lymphocytes

Interleukin 2 (IL-2) was shown to induce a small but significant increase in the level of cGMP after 20 min stimulation and a subsequent fall after 1 h in activated T lymphocytes. No change in the level of cAMP was observed. Addition of the cyclic nucleotide analogues dbcAMP or dbcGMP did not stimulate DNA synthesis. On the contrary, IL-2-induced [3H]thymidine incorporation was inhibited by these drugs. Further, the phosphodiesterase inhibitor theophylline inhibited proliferation of activated T lymphocytes. Our results indicate that neither cAMP nor cGMP act as 'second messengers' for IL-2 but support the theory that cAMP is a negative regulator of cell proliferation.

Antibody binding to CD5 (Tp67) and Tp44 T cell surface molecules: effects on cyclic nucleotides, cytoplasmic free calcium, and cAMP-mediated suppression

T cells can be activated to proliferate by antibodies to the T cell antigen receptor or the molecularly associated CD3 complex if monocytes are present. We have shown previously that monoclonal antibodies to the human T cell differentiation antigens CD5 (Tp67) and Tp44 each augment and prolong proliferative responses of anti-CD3-activated T cells, even in the absence of monocytes. Here we show that the functional and biochemical mechanisms of CD5 and Tp44 signal transmission are distinct. T cell proliferation is suppressed by agents that increase the concentration of intracellular cAMP. We found that antibody binding to the Tp44 surface molecule overcomes this suppression, whereas antibody binding to CD5 does not, indicating that ligand-Tp44 interaction changes T cell sensitivity to cAMP-mediated growth inhibition. The ability of anti-CD3, anti-Tp44, and anti-CD5 monoclonal antibodies to directly alter cyclic nucleotide levels in the Jurkat T cell line was examined. Anti-CD3 alone caused a rapid four- to sixfold increase in cAMP levels, but did not affect cGMP levels. However, anti-Tp44 and anti-CD5 each caused a rapid three- to fourfold increase in cGMP levels without affecting cAMP levels. In other experiments, cytoplasmic free calcium levels were measured in resting T cells after CD5 or Tp44 stimulation by using the dye indo-1 and flow cytometry. This sensitive method showed that anti-CD5 alone caused an increase in cytoplasmic calcium free levels within 3 min of antibody addition, whereas anti-Tp44 had no effect. Finally, anti-Tp44 and IL 1 each augmented proliferation of phorbol ester-stimulated lymphocytes, whereas anti-CD5 did not. The effects of IL 1 and Tp44 could be further distinguished in that the effect of anti-Tp44 was resistant to inhibition by dBcAMP whereas IL 1 was not. These data suggest that the receptor function of both Tp44 and CD5 involves changes in cyclic nucleotides levels, and that the mechanism by which anti-Tp44 and anti-CD5 antibodies affect T cell proliferative responses may be related to their selective effects on cGMP levels and cytoplasmic calcium concentrations.

Regulation of salt and water transport across airway mucosa

Effective mucociliary clearance of secretions by airway mucosa requires efficient ciliary beating. The structure of airway secretions provides for this requirement by having a viscous mucous layer touched underneath and propelled by ciliary tips, while the rest of the cilium is surrounded by a serous fluid layer. The regulation of the latter layer is thought to be a function of mucosal epithelial cells capable of active ion transport. Mammalian medium-sized bronchi actively absorb sodium, whereas the tracheal mucosae of several mammals are capable of sodium absorption as well as chloride secretion. By generating local osmotic gradients, these ion transport processes may regulate the depth of the periciliary sol layer. These transport processes generate an electrical PD across the mucosa such that the luminal side is negatively charged in reference to the submucosal side (electrogenic transport). Transport of sodium and chloride across the plasma membrane is against a steep electrochemical gradient, and cellular energy resources are utilized for this purpose (active transport). Chloride transport is coupled to sodium transport; therefore, inhibition of the sodium pump (Na-K-ATPase) with ouabain leads to inhibition of sodium as well as chloride transport. Several neurohumoral agents have been found to stimulate chloride secretion, such as PGs, beta-adrenergic agonists, VIP, substance P, and bradykinin. Mechanisms of regulation of sodium transport by airway epithelia are not clearly understood. Available evidence suggests that elevation of cellular PGs, cAMP, and calcium enhances apical cell-membrane conductance to chloride ion, with an opposite effect on sodium conductance. Therefore, it seems reasonable to suggest that neurohumoral control mechanisms may switch from sodium and fluid absorption to chloride and fluid secretion, and vice versa. Several lines of evidence support this proposal. First, the lung of fetal lamb secretes chloride and fluid in utero; this activity ceases at birth, when the catecholamine level is increased, causing a decrease in chloride secretion. In contrast, adult sheep trachea absorbs sodium. Second, agents that stimulate chloride secretion in bovine trachea concomitantly reduce sodium absorption, and vice versa. Similar observations were noted in some instances in dog trachea. Third, whereas unstimulated ferret and cat tracheas only absorb sodium, they secrete chloride upon exposure to beta agonists.(ABSTRACT TRUNCATED AT 400 WORDS)

Selective regulation of trypsin gene expression by calcium and by glucose starvation in a rat exocrine pancreas cell line

Treatment of the rat pancreatic acinar cell line AR4-2J with the calcium ionophore A23187 selectively increases, within a few hours, the steady-state level of trypsin mRNA. Addition of the tumor-promoting phorbol ester phorbol 12-myristate 13-acetate potentiates the calcium-induced increase. The mRNA level of the other tested exocrine pancreatic genes decreases. These results were confirmed by DNA transfection experiments, using the 5' flanking region of the trypsin and chymotrypsin genes linked to the coding sequence of the chloramphenicol acetyltransferase (CAT) gene. In calcium-induced cells transfected with the trypsin constructs, an increase in CAT activity was observed, whereas the chymotrypsin constructs revealed a decreased CAT activity. Glucose starvation of AR4-2J cells similarly elicited a selective increase in trypsin mRNA. This selective regulation of trypsin may reflect its role as the key activator of the other zymogen species.

Spatial and temporal organization of intracellular adenine nucleotides and cyclic nucleotides in relation to rhythmic motility in Physarum plasmodium

Spatio-temporal organization of a migrating plasmodium was studied both by analysing intracellular concentrations of adenine and cyclic nucleotides and by applying image processing for recording oscillatory changes in thickness with use of microcomputers. ATP and ADP concentrations were about twice as high in the front as in the rear, while AMP distributed uniformly. On the other hand, cAMP and cGMP concentrations were several times higher in the rear than in the front, showing oscillations in between. The cAMP concentrations at the front oscillated with a phase advancing about one-third of the period with respect to the phase of the thickness oscillation, while cGMP concentration there varied only little. ATP concentration oscillated concomitantly with H+. A feedback control loop consisting of (ATP-H+)-cAMP-Ca2+ is proposed. The possible mechanism of rhythmic contractions involving mitochondria which may excrete pulses of Ca2+ and induce cell polarization is discussed.

Cerebellar cyclic nucleotides and the development of convulsion, with reference to the anticonvulsant activity of diazepam

Dibutyryl cyclic GMP (DbcGMP) or dibutyryl cyclic AMP (DbcAMP) given to rats intracerebellarly in a dose of 200 nmol/head produced electroencephalographic convulsive changes. Intracerebellar (i.c.) administration of lower doses (100 nmol/head) of DbcGMP and DbcAMP and 200 nmol/head of norepinephrine (NE) and glutamate (Glu) facilitated the pentylenetetrazol (PTZ)-induced convulsions. Diazepam (100 nmol/head, i.c.) suppressed the PTZ-induced convulsions. GABA (400 nmol/head, i.c.) did not affect the PTZ-induced convulsions. These results suggest that DbcGMP, DbcAMP and Glu inhibit seizure control mechanisms in the cerebellum, and that one of the sites of the anticonvulsant action of diazepam is located in the cerebellum.

Prospective strategies for cholinergic interventions in Alzheimer's disease

The cholinergic hypothesis of memory dysfunction has guided most of the recent proposals for treating the primary symptoms of AD. The efficacy of these treatments has been severely limited. This review examines two major lines of evidence which suggest that the cholinergic hypothesis may have to be expanded and revised. The cholinergic hypothesis focuses on pre-synaptic defects. It assumes cholinoceptive neurons would function normally with adequate stimulation. Evidence is not sufficient to support this assumption. In addition, dissociations have been demonstrated between muscarinic receptor number and functional response of cholinoceptive neurons. Various measures are proposed to investigate the functional integrity of muscarinic receptors in AD patients. AD often has been characterized as a disorder produced by generalized cholinergic hypoactivity. Evidence for cortisol hypersecretion, abnormal dexamethasone suppression, and the occurrence of depressive symptoms, motoric dysfunction and sleep abnormalities in AD patients is more consistent with regional cholinergic hyperactivity than generalized hypoactivity. Resolution of these discrepancies could shed new light on the pathophysiology and treatment strategies for AD. Cholinoceptive neurons could be hypersensitive, subsensitive or have unaltered responsivity. These options would have very different treatment implications. New developments in outcome assessment which are capable of discriminating varieties of differential response to treatment can spur treatment development and improve quality of care for patients with complex disorders such as AD.

[Cyclic nucleotides and lipids in the realization of the radioprotective effect of ceruloplasmin]

Ceruloplasmin administered 60 min before irradiation diminished cAMP and cGMP levels, which were increased by irradiation at LD50 and LD100, and normalized cAMP/cGMP ratio in the rat liver during the first 24 h following irradiation with a dose of 6.24 Gy. The content of phospholipids increased and that of cholesterol decreased under the effect of ceruloplasmin leading to normalization of the molar cholesterol/phospholipid ratio in the rat liver on the 7th day of radiation sickness (LD50, 6.24 Gy).

Cyclic nucleotides in muscarinic regulation of DNA and RNA polymerase activity in cultured corneal epithelial cells of the rabbit

DNA and RNA polymerase activities in the purified nuclear fraction from cultured rabbit corneal epithelial cells were assayed over a range of substrate (labeled dTTP or UTP) concentrations using calf thymus DNA as template. Effects of carbamylcholine on polymerase activities were evaluated over a range of drug concentrations including those saturating muscarinic receptors. Carbamylcholine significantly (p less than 0.001) enhanced activity of both polymerases, both in nuclei incubated with the drug during assay and in nuclei from carbamylcholine-treated cells. Drug effects were blocked by atropine. Regression analysis of Hill plots for variation of polymerase activity with carbamylcholine concentration indicated half-maximal activity of both polymerases at approximately 1 microM carbamylcholine. Mechanisms by which carbamylcholine may alter polymerase activities are discussed in relation to effects of the drug on nuclear enzymes of cyclic nucleotide metabolism and on cyclic nucleotide-dependent protein phosphorylation.

Pharmacologic approaches to obstructive airway disease

We have outlined the various bronchodilator medications currently employed in chronic obstructive airways disease. A knowledge of the pharmacology of the lung and the sites of action of these medications should make it possible to combine them in ways that will promote the most benefit for the patient with the least side effects. A logical format for approaching the patient with chronic obstructive airways disease is listed below. Frequently, for the patient with mild or intermittent symptoms of airways obstruction, an inhaled beta agonist will suffice. This may be taken regularly and as needed (for example, prior to vigorous exercise). For patients with more symptoms or those who cannot be controlled on a single agent, a long-acting theophylline preparation should be initiated. Usually, a 12-hour sustained release tablet is preferable. Bedtime dosing may prevent nocturnal shortness of breath. The factors affecting theophylline metabolism should be kept in mind, and theophylline levels should be obtained in those situations where there is an inadequate or inappropriate clinical response. The combination of an oral theophylline and an inhaled beta agonist should suffice in approximately 80 per cent of patients with chronic obstructive airways disease. For those patients who still have symptoms and in whom no other precipitating factor, such as infection or allergy, has been defined, additional therapy can be initiated. For outpatients, this usually consists of the addition of an oral beta agonist, starting at the lowest dose first. If tachyphylaxis appears to be developing, then aerosol atropine or initiation of corticosteroids should be considered. The addition of mucolytics, mist, and chest physiotherapy will frequently reduce the need for additional measures.

Regulation of plasminogen activator production by bone-resorbing hormones in normal and malignant osteoblasts

The plasminogen activator (PA) activity of clonal rat osteogenic sarcoma cell (phenotypically osteoblast) and of osteoblast-rich rat calvarial cells is shown to be increased by treatment with the bone-resorbing hormones, PTH, 1,25-dihydroxyvitamin D3, prostaglandin E2, and epidermal growth factor. Dose-dependent increases were observed, after a lag period of 4 to 8 h. Stimulated and control PA activities were inhibited by actinomycin D and cycloheximide but not by cytosine arabinoside. Glucocorticoid hormones prevented the hormone stimulation, but other steroids did not. Calcitonin had no effect either on basal or on hormone-treated PA activity. Isobutyl-methylxanthine alone increased PA activity and enhanced responsiveness to PTH and to prostaglandin E2. These data point to a common pathway in the actions upon osteoblasts of several hormones with diverse initial cellular actions and raise the possibility that the PA/plasmin system may contribute to cellular mechanisms of bone turnover.

The pharmacology of fever

The ability to minimise, if not prevent, large variations in deep body temperature that would otherwise result from some environmental conditions is a homeostatic function of unquestioned benefit that is demonstrated only by the more highly evolved animals. Nevertheless, body temperature is raised above normal values in many pathological conditions. This increase in temperature or fever is an active and co-ordinated response, which indicates the involvement of the CNS. Central injection and lesion studies have shown that the brain, in particular the PO/AH, is the site of action of fever-inducing agents, termed pyrogens. Electrophysiological data show that pyrogens modify the activity of central thermosensitive neurones as if to increase heat gain and decrease heat loss. The common response of fever to pyrogens of diverse origins is attributable to fever being mediated by an endogenous pyrogen released by phagocytic cells in the host. The mechanism by which central neuronal function is disturbed by pyrogens present in the periphery is not known. Tracer studies have yet to demonstrate the passage of a pyrogen across the blood-brain barrier. The possible involvement of several putative neurotransmitters and modulators in fever has been reviewed here, but most compounds have not been studied sufficiently to allow firm conclusions to be drawn. Much of the data is limited to the effects of the putative mediators on normal thermoregulation but, even when the effect is hyperthermia, such observations do not necessarily indicate a role for the endogenous material in fever. Dose-response curves for agonists and the effects of antagonists are often undetermined. This shortfall in data is due to some extent to the nature of fever; a central response in vivo over several hours. Although fever may enhance other host reactions to combat infection and inflammation, neither this benefit nor the undesirability of antipyretic therapy has been demonstrated unequivocally in either homeothermic laboratory animals or humans. Consequently, antipyretic drugs continue to be used clinically to alleviate the fever, malaise and/or pain commonly associated with disease. The drugs in common usage are the nonsteroidal antipyretic analgesics, many of which also have an anti-inflammatory effect. The primary mode of action of these drugs as antipyretics appears at present to be the inhibition of cyclo-oxygenase and a consequent reduction of prostanoid material in pyrogen-sensitive areas of the brain.(ABSTRACT TRUNCATED AT 400 WORDS)

[Function of neutrophilic polymorphonuclear leukocytes in pediatric patients with intrinsic and extrinsic asthma during the intercrisis period]

Polymorphonuclear leukocyte function: chemotaxis, NBT and myeloperoxidases activity, was investigated in a group of asthmatic pediatric patients, 26 with intrinsic and 27 with extrinsic asthma, during intercrisis. There was no difference between the extrinsic asthma group and the control one while the group with intrinsic asthma showed an increase of chemotaxis activity (p less than 0.001) and NBT reduction (p less than 0.01); myeloperoxidases activity was similar to the control group. The comparative study of the two types of asthma shows a significant increase of NBT reduction (p less than 0.02) and chemotaxis activity (p less than 0.001) in the intrinsic group. These findings demonstrate that polymorphonuclear function is different in the two main types of asthma during the asymptomatic period.

[Cyclic nucleotides and calcium ions in the activation of B-lymphocyte movement in mice by an anti-immunoglobulin serum]

It was shown that B lymphocyte motility activated by anti-immunoglobulin serum may be abrogated in a Na+-deficient medium and in a 10(-5)M trifluoperazine-containing medium but not in a Ca2+-deficient medium. The tetracycline fluorescence test demonstrated Ca2+ efflux from isolated B lymphocyte mitochondria due to Na+ exposure. The radioimmunoassay demonstrated the cGMP level to rise after exposure to anti-immunoglobulin serum. The Na+-dependent Ca2+ efflux from the mitochondria might be the main mechanism in anti-immunoglobulin serum activation of B lymphocytes and in the cGMP level rising.

Histone and high mobility group protein phosphorylation in the thyroid: regulation by cyclic nucleotides

A variety of cyclic nucleotide analogs and other agents that affect thyroid cyclic nucleotide metabolism were used to investigate the role of cAMP and cGMP in regulating nuclear protein phosphorylation in calf thyroid slices labeled in vitro with [32P]orthophosphate. Two major groups of acid-soluble proteins were studied. Group I consisted of proteins whose phosphorylation is stimulated by TSH [histones H1 and H3, high mobility group (HMG) protein 14, and the HMG 14/17-like protein PS.3]; group II included representatives of a spectrum of proteins whose phosphorylation is unaffected by TSH (histones H2A, H2B, and H4, HMG 17, the HMG 14/17-like protein PS.2, and the nonhistone protein AS.1). The effects of TSH (50 mU/ml) on the 32P labeling of group I proteins were partially reproduced by (Bu)2cAMP (1 mM), 8-bromo-cAMP (1 mM), and butyrate (2 mM), and closely mimicked by 8-(4-chlorophenylthio)cAMP (1 mM), forskolin (25 microM), and butyrate (10 mM). (Bu)2cGMP (1 mM), 8-bromo-cGMP (1 mM), and carbachol (50 microM) had no effect on protein phosphorylation. NaNO2 (20 mM), which markedly increases cGMP concentration in calf thyroid slices, decreased the 32P labeling of group I proteins and also affected, to varying extents, the phosphorylation of the group II proteins. The phosphodiesterase inhibitor methylisobutylxanthine (0.5 mM) had generally minor effects on 32P labeling; however, it did counteract the effects of NaNO2 on group I protein phosphorylation. Our results provide strong support for the hypothesis that TSH-dependent phosphorylation of group I proteins is mediated by cAMP, but they provide little evidence of cGMP regulation of histone or HMG protein phosphorylation.

Some aspects of the phosphorylation of phenylalanine 4-monooxygenase by a calcium-dependent and calmodulin-dependent protein kinase

A calmodulin-dependent protein kinase purified from liver catalyzed the incorporation of up to 0.7 mol of phosphate per mol subunit of phenylalanine 4-monooxygenase. The phosphorylation was accompanied by a proportional increase in the hydroxylase activity. The reaction was Ca2+-dependent and was inhibited by physiological concentrations of phenylalanine. Phenylalanine 4-monooxygenase was also a substrate for the cGMP-dependent protein kinase, but in this system phenylalanine stimulated the rate of phosphorylation to a similar extent as that observed in the reaction catalyzed by cAMP-dependent protein kinase. The hydroxylase was not a substrate for phosphorylase kinase. The calmodulin-dependent reversal of the kinase reaction in the presence of MgADP, was also inhibited by phenylalanine. Since the kinetics of the reverse reaction was the same using 32P-hydroxylase phosphorylated by calmodulin-dependent and cAMP-dependent kinases, it is likely that both kinases phosphorylate the same site on the enzyme. This conclusion was further supported by peptide mapping of tryptic and peptic digests of 32P-hydroxylase, which revealed one major phosphopeptide with enzyme phosphorylated by either kinase. The Ca2+-dependent and calmodulin-dependent phosphorylation described above may mediate the increased phosphorylation of the hydroxylase [Garrison, J. C., Johnsen, D. E., and Campanile, C. P. (1984) J. Biol. Chem. 259, 3283-3292] and its increased activity [Fisher, M. J., Santana, M. A., and Pogson, C. I. (1984) Biochem. J. 219, 87-90] recently observed in hepatocytes exposed to Ca2+-elevating agents.