Properties and functions of calmodulin

Calmodulin in Paramecium: Focus on Genomic Data

Calcium (Ca²⁺) is a universal second messenger that plays a key role in cellular signaling. However, Ca²⁺ signals are transduced with the help of Ca²⁺-binding proteins, which serve as sensors, transducers, and elicitors. Among the collection of these Ca²⁺-binding proteins, calmodulin (CaM) emerged as the prototypical model in eukaryotic cells. This is a small protein that binds four Ca²⁺ ions and whose functions are multiple, controlling many essential aspects of cell physiology. CaM is universally distributed in eukaryotes, from multicellular organisms, such as human and land plants, to unicellular microorganisms, such as yeasts and ciliates. Here, we review most of the information gathered on CaM in Paramecium, a group of ciliates. We condense the information here by mentioning that mature Paramecium CaM is a 148 amino acid-long protein codified by a single gene, as in other eukaryotic microorganisms. In these ciliates, the protein is notoriously localized and regulates cilia function and can stimulate the activity of some enzymes. When Paramecium CaM is mutated, cells show flawed locomotion and/or exocytosis. We further widen this and additional information in the text, focusing on genomic data.

Use of allosteric targets in the discovery of safer drugs

The need for drugs with fewer side effects cannot be overemphasized. Today, most drugs modify the actions of enzymes, receptors, transporters and other molecules by directly binding to their active (orthosteric) sites. However, orthosteric site configuration is similar in several proteins performing related functions and this leads to a lower specificity of a drug for the desired protein. Consequently, such drugs may have adverse side effects. A new basis of drug discovery is emerging based on the binding of the drug molecules to sites away (allosteric) from the orthosteric sites. It is possible to find allosteric sites which are unique and hence more specific as targets for drug discovery. Of many available examples, two are highlighted here. The first is caloxins - a new class of highly specific inhibitors of plasma membrane Ca²⁺ pumps. The second concerns the modulation of receptors for the neurotransmitter acetylcholine, which binds to 12 types of receptors. Exploitation of allosteric sites has led to the discovery of drugs which can selectively modulate the activation of only 1 (M1 muscarinic) out of the 12 different types of acetylcholine receptors. These drugs are being tested for schizophrenia treatment. It is anticipated that the drug discovery exploiting allosteric sites will lead to more effective therapeutic agents with fewer side effects.

Inhibition of Nav1.7 and Nav1.4 sodium channels by trifluoperazine involves the local anesthetic receptor

The calmodulin (CaM) inhibitor trifluoperazine (TFP) can produce analgesia when given intrathecally to rats; however, the mechanism is not known. We asked whether TFP could modulate the Na(v)1.7 sodium channel, which is highly expressed in the peripheral nervous system and plays an important role in nociception. We show that 500 nM and 2 muM TFP induce major decreases in Na(v)1.7 and Na(v)1.4 current amplitudes and that 2 muM TFP causes hyperpolarizing shifts in the steady-state inactivation of Na(v)1.7 and Na(v)1.4. CaM can bind to the C-termini of voltage-gated sodium channels and modulate their functional properties; therefore we investigated if TFP modulation of sodium channels was due to CaM inhibition. However, the TFP inhibition was not replicated by whole cell dialysis of a calmodulin inhibitory peptide, indicating that major effects of TFP do not involve a disruption of CaM-channel interactions. Rather, our data show that TFP inhibition is state dependent and that the majority of the TFP inhibition depends on specific amino-acid residues in the local anesthetic receptor site in sodium channels. TFP was also effective in vivo in causing motor and sensory blockade after subfascial injection to the rat sciatic nerve. The state-dependent block of Na(v)1.7 channels with nanomolar concentrations of TFP raises the possibility that TFP, or TFP analogues, might be useful for regional anesthesia and pain management and could be more potent than traditional local anesthetics.

Involvement of calmodulin inhibition in analgesia induced with low doses of intrathecal trifluoperazine

We examined which of the known properties of trifluoperazine, including calmodulin inhibition, are involved in its analgesic effect. Furthermore, we tried to find any possible interaction between opioidergic system and calmodulin inhibition-induced analgesia. Intrathecal trifluoperazine (1, 10, 100 microg) showed a biphasic effect in the formalin test; i.e., analgesia at relatively low doses (1, 10 microg) and hyperalgesia at a high dose (100 microg). No analgesic effects were observed after intrathecal injection of sulpiride (1, 10, 100 microg), atropine (0.1, 1, 10 microg), phentolamine (0.1, 1, 10 microg) and brompheniramine (0.1, 1, 10 microg). Meanwhile, intrathecal calmidazolium (10, 50, 250 microg) induced a dose-dependent analgesia. Histamine (1 microg), physostigmine (1 microg), bromocriptine (1 microg) and norepinephrine (1 microg) did not affect trifluoperazine-induced analgesia. Calcium (20 microg) attenuated the antinociceptive effect of trifluoperazine and inhibited the analgesic effect of calmidazolium. Finally, naloxone (2 mg/kg) decreased trifluoperazine-induced antinociception but did not have any effects on calmidazolium-induced analgesia. We concluded that calmodulin inhibition may be involved in the analgesia produced by trifluoperazine. With increasing doses of trifluoperazine, the algesic effect seems to overcome the analgesic effect. It is also suggested that the opioidergic system does not interact with calmodulin inhibition-induced analgesia even though this system has a possible role in trifluoperazine-induced analgesia.

Hydrogen peroxide-induced cytoskeletal rearrangement in cultured pulmonary endothelial cells

Although the signaling pathways leading to hydrogen peroxide (H2O2)-induced endothelial monolayer permeability remain ambiguous, cytoskeletal proteins are known to be essential for maintaining endothelial integrity and regulating solute flux through the monolayer. We have recently demonstrated that thrombin-induced actin reorganization in bovine pulmonary artery endothelial cells (BPAEC) requires activation of both myosin light chain kinase (MLCK) and protein kinase C (PKC). Therefore, the present study was designed to investigate the effects of H2O2 on actin reorganization in BPAEC. H2O2 initiated sustained recruitment of actin to the cytoskeleton and transient myosin recruitment in a time- and concentration-dependent manner. The H2O2-induced actin recruitment was significantly inhibited by the calmodulin antagonists, W7 and TFP, but not by the MLCK inhibitor, KT5926, nor the PKC inhibitors, H7 and calphostin C. H2O2 also caused actin filament rearrangement in BPAEC with disruption of the dense peripheral bands and formation of stress fibers. These alterations occurred prior to actin translocation to the cytoskeleton and are prevented by inhibition of either MLCK or PKC. High concentrations of H2O2 transiently attenuated PKC activity but slightly increased the phosphorylation of the prominent PKC substrate and actin-binding protein, myristoylated alanine-rich C kinase substrate (MARCKS), by 5 min. However, MARCKS phosphorylation was reduced to below basal levels by 30 min. On the other hand, H2O2 induced a time- and dose-dependent phosphorylation of myosin light chains which was eliminated by both MLCK and PKC inhibitors. These data suggest that MLCK contributes to H2O2-induced myosin light chain phosphorylation and actin rearrangement and that PKC may play a permissive role. Neither of these enzymes appears to be involved in the H2O2-induced recruitment of actin to the cytoskeleton.

Droperidol inhibits tracheal contraction induced by serotonin, histamine or carbachol in guinea pigs

PURPOSE

Droperidol (D) is effective in the treatment of patients with status asthmaticus. It has been reported that D inhibits the bronchoconstriction induced by serotonin (5-HT) but not that by histamine (H) or acetylcholine. However, haloperidol, another butyrophenone, is known to interact with and inhibit calmodulin, an intracellular Ca(++)-binding protein which is important in the contraction of smooth muscles. The present study was designed to investigate the effects of D on tracheal contractions induced by 5-HT, H or carbachol (C) and to determine the contribution of alpha-adrenoceptors to the relaxant effect of D in vitro.

METHODS

Tracheas of female guinea pigs were cut spirally into strips and mounted in water-jacketed organ baths in Tyrode's solution, aerated with a mixture of 95% O2 and 5% CO2 at 37 degrees C. The changes in isometric tension induced by each spasmogen in the strips were measured with a transducer and a polygraph.

RESULTS

We found that D inhibited the tracheal contractions induced by 5-HT, H or C in a concentration-dependent manner. At 1.25 x 10(-6) M D blocked the effect of 10(-4) M 5-HT by 44.1 +/- 4.3% and at 2.5 x 10(-6) M by 63.8 +/- 3.8%. Similarly, at 5.0 x 10(-6) M concentration, D blocked the effect of 10(-5) M H by 27.7 +/- 5.3% and at 10(-5) M by 56.2 +/- 2.6%. Furthermore, 5 x 10(-6) M of D reduced the contractions produced by 10(-7) M C by 37.1 +/- 3.0% and 10(-5) M of D by 76.1 +/- 3.2%. The inhibiting effect of D was strongest on contractions induced by 5-HT. Prazosin (10(-6) M) affected neither 5-HT-induced contractions nor the inhibition by D.

CONCLUSION

Our data indicate that D partially blocks the contractile responses not only to 5-HT, an effect which would be mediated through a blockade of the 5-HT receptors, but also to H or C, probably through inhibition of calmodulin. Our data support previous reports indicating that droperidol may be an important therapeutic agent in the treatment of patients with hyperreactive airways.

Calmodulin and in vitro regenerating frog sciatic nerves: release and extracellular effects

Although calmodulin (CaM) is commonly considered to be an intracellular protein, it has been suggested lately that it is released and exerts functions extracellularly. In the present investigation this was studied in in vitro regenerating adult frog (Rana temporaria) sciatic nerves. Using a multi-compartment incubation chamber, the non-neuronal cells in the outgrowth region of such nerves were radiolabelled with amino acid precursors. Based on immunological criteria, these cells were shown to release CaM. When the nerves were treated with CaM, both the outgrowth of sensory axons and the injury-induced proliferation of non-neuronal cells were partially inhibited. The inhibitory effects occurred even when the incubation medium contained as little as 30 pM CaM. Furthermore, treatment with anti-CaM antibodies resulted in reduced outgrowth, which suggested that during normal conditions extracellular CaM is kept at an optimal concentration. Finally, conditioned medium was found to contain several CaM-binding proteins. The present findings may reflect an earlier unknown function of extracellular CaM in controlling various growth mechanisms in integrated tissues.

Binding of [3H]SCH23390 to a non-dopaminergic site in bovine kidney

Binding of the D1 dopamine receptor antagonist [3H]SCH23390 to bovine renal cortical membranes has been studied. Specific binding of [3H]SCH23390 was saturable and reversible and stereoisomers of SCH23390 competed stereoselectively. In contrast, competition with the isomers of butaclamol was not stereoselective and dopamine failed to compete for the [3H]SCH23390 binding site. The site is therefore not a D1 dopamine receptor. Competition studies with a very wide range of compounds failed to define the nature of the [3H]SCH23390 binding sites in renal cortex whereas in parallel studies the characteristics of [3H]SCH23390 binding in caudate nucleus were entirely consistent with those of D1 dopamine receptors. The nature of [3H]SCH23390 binding in preparations of tubular and glomerular membranes was found to be virtually identical to those of crude renal cortical membranes indicating lack of compartmentation of these sites. Autoradiographic studies of [3H]SCH23390 binding in bovine kidney showed significantly higher levels of binding sites in renal cortex compared with renal medulla and this was confirmed by direct ligand binding studies.

Mechanisms of lead neurotoxicity

During the past several years, there has been a renewed interest in the mechanisms by which lead poisoning disrupts brain function. In part, this is related to clinical observations that imply an absence of threshold for toxicity in the immature brain. Many of the neurotoxic effects of lead appear related to the ability of lead to mimic or in some cases inhibit the action of calcium as a regulator of cell function. At a neuronal level, exposure to lead alters the release of neurotransmitter from presynaptic nerve endings. Spontaneous release is enhanced and evoked release is inhibited. The former may be due to activation of protein kinases in the nerve endings and the latter to blockade of voltage-dependent calcium channels. This disruption of neuronal activity may, in turn, alter the developmental processes of synapse formation and result in a less efficient brain with cognitive deficits. Brain homeostatic mechanisms are disrupted by exposure to higher levels of lead. The final pathway appears to be a breakdown in the blood-brain barrier. Again, the ability of lead to mimic or mobilize calcium and activate protein kinases may alter the behavior of endothelial cells in immature brain and disrupt the barrier. In addition to a direct toxic effect upon the endothelial cells, lead may alter indirectly the microvasculature by damaging the astrocytes that provide signals for the maintenance of blood-brain barrier integrity.

Divalent cation dependence of the inhibition by phenothiazines of mediator release from mast cells

1. The divalent cations calcium, strontium and barium--and in that order of decreasing effectiveness--were capable of supporting the stimulated release of histamine from rat peritoneal mast cells (RPMC). 2. The responsiveness of mast cells to stimulation in the presence of divalent cations was, in general, markedly enhanced when the cells were first depleted of their intracellular calcium stores. 3. The putative calmodulin antagonists, chlorpromazine, promethazine, thioridazine (phenothiazines) and W-7 (a naphthalene sulphonamide) all inhibited histamine release in the presence of divalent cations in both untreated cells and in RPMC depleted of their intracellular calcium. 4. Histamine release induced by antigen, compound 48/80 and ionophore A23187 was inhibited by this class of compounds most effectively in the presence of extracellular barium, less so in the presence of strontium and least so in calcium-containing media. 5. In the experimental situation where the extracellular calcium concentration was reduced (less than 1 mM), the phenothiazines inhibited the stimulated release of histamine more effectively. 6. In toto, these results suggest that strontium and barium, as well as calcium, can support histamine release from RPMC by directly interacting with an intracellular divalent cation-binding site that may be calmodulin. As a consequence, one mechanism by which the phenothiazines and W-7 may modulate the secretory response could reflect an antagonism of a divalent cation interaction at that same site, although other additional potential sites of inhibitory action are indicated, dependent on the stimulus employed for secretion.

Characteristics of the binding of phenoxybenzamine to calmodulin

To determine the factors that influence the interaction between phenoxybenzamine and calmodulin, the binding of phenoxybenzamine to calmodulin was determined by equilibrium dialysis under a variety of experimental conditions. This interaction was found to be similar in some respects to the interaction between phenothiazines and calmodulin. It was saturable, with between 1 and 2 mol of phenoxybenzamine bound to 1 mol of calmodulin. It was also dependent upon temperature, the presence of a divalent cation such as calcium, and on pH, showing maximum binding at pH 6.5 with little binding at pH values below 4.2 or above 8.0. The site at which phenoxybenzamine bound to calmodulin appears to be similar to that at which certain antipsychotic agents bind, since several of them, including penfluridol, pimozide and spiroperidol, prevented the binding of phenoxybenzamine to calmodulin. However, in contrast to the reversible binding of most phenothiazines to calmodulin, phenoxybenzamine bound to calmodulin irreversibly. The binding of phenoxybenzamine to calmodulin was fairly selective in that other alpha-adrenergic agents such as prazosin, yohimbine and clonidine failed to bind to calmodulin when examined under the same experimental conditions. In addition, phenoxybenzamine showed little or no calcium-dependent binding to the S-100 protein, bovine serum albumin or cytochrome c. The irreversible complex between phenoxybenzamine and calmodulin may be useful for inhibiting certain calmodulin-dependent reactions and for studying the various biological functions of calmodulin.

Calmodulin-dependent phosphatases of PC12, GH3, and C6 cells: physical, kinetic, and immunochemical properties

Calmodulin-dependent phosphoprotein phosphatase (CaMDP) activity has been found in each of three cultured cell lines: rat pheochromocytoma (PC12), glioma (C6), and pituitary adenoma (GH3) cells. These CaMDP activities bind to immobilized calmodulin in the presence of Ca2+ and are eluted by EGTA. Sucrose density centrifugation revealed that the phosphatase activities exhibited sedimentation coefficients of 4.37, 4.23, and 4.59 for proteins derived from C6, GH3, and PC12 cells, respectively. The Stokes radii measured for the PC12 and C6 activities were 41.8 and 40.0 A, respectively. The estimated molecular weights calculated for the enzymes from these data are 79,100 and 72,200. The phosphatase activities required the presence of divalent cations such as Ca2+ or Mn2+ for expression of activity, which was optimal only in the presence of calmodulin. The apparent Km for phosphorylated myelin basic protein substrate was 8 microM. Affinity-purified antibodies to the B subunit of bovine brain CaMDP were found by immunoblot (Western blot) to cross-react with a single protein among proteins extracted from PC12, C6, and GH3 cells that had been resolved by two-dimensional electrophoresis. In each case, the cross-reacting protein exhibited an Mr of 16,000 and an isoelectric point of 4.7, values virtually identical to those reported previously for the B subunit of bovine brain CaMDP (sometimes called calcineurin). This cross-reacting protein was found among cellular proteins eluted from immobilized calmodulin by EGTA. Immunocytochemical localization of the cross-reacting protein in undifferentiated PC12 cells or in cells differentiated in response to nerve growth factor revealed its presence diffusely throughout the cytoplasm. These experiments support the contention that each of these cell lines contains a calmodulin-regulated phosphatase homologous physically and kinetically, and immunologically related to bovine brain CaMDP.

Compartmentalization of calmodulin and tubulin in the male C57BL/6J mouse brain: heterogeneity of age changes in calmodulin compartments

Calmodulin (CaM) and tubulin were analyzed by radioimmunoassay in subcellular fractions prepared from cerebral cortex and striatum of aging male C57BL/6J mice. Three fractions were prepared by a new procedure: cytosol (soluble); EGTA-releasable, membrane-bound; and detergent-extractable (Triton X-100), membrane-bound fractions. CaM concentration in all three fractions prepared from striatum showed small (10-15%, p less than 0.05) decreases with age (3-31 months). Cortical CaM concentrations were less affected by age, and only the EGTA-releasable fraction decreased. To compare functional activity and immunoreactivity of CaM, soluble CaM was also assayed by the activation of cyclic nucleotide phosphodiesterase (PDE). The radioimmunoassay and PDE activation assays gave equivalent results, suggesting that no alteration occurred with age in biological activity of CaM, via post-translational modification or other mechanisms. Soluble and particulate tubulin concentration did not change significantly with age in either brain region. The changes observed in striatal CaM, particularly in membrane-bound compartments, could contribute to the age-related decline in mammalian basal ganglial function.

Calmodulin-mediated cadmium inhibition of phosphodiesterase activity, in vitro

Ion-stripped bovine brain calmodulin (CaM) binds 4 moles Cd2+ as well as 4 moles Ca2+ per mole protein, with similar affinity; in the presence of 1 mM Mg2+ the molar binding ratio of CaM for Ca2+ decreased to 3, the apparent K0.5 for Ca2+ nearly doubled, but the binding characteristics of CaM for Cd2+ were not changed. Saturating concentrations Ca2+ did not affect the molar binding ratio of CaM for Cd2+, but increased the apparent K0.5 for Cd2+; vice versa, saturating concentrations Cd2+ decreased the molar binding ratio for Ca2+ to 2 without affecting the apparent K0.5 for Ca2+. CaM-independent phosphodiesterase (PDE) activity was inhibited at [Cd2+] greater than 10(-5) M. Cd2+-CaM as well as Ca2+-CaM activated PDE. However, the Cd2+-CaM complex is less effective than the Ca2+-CaM complex in stimulating CaM-dependent enzyme activities. Cd2+ inhibits Ca2+- and CaM-dependent PDE in a competitive way. Introduction of Cd2+ in a medium containing Ca2+ and CaM may, therefore, result in a reduction of CaM-dependent enzyme stimulation. By its interference with Ca2+- and CaM- dependent PDE activity, Cd2+ could upset the catabolic pathway of cellular cyclic nucleotide metabolism.

Calmodulin-binding proteins and calmodulin-regulated enzymes in dog pancreas

Calmodulin was isolated and purified to homogeneity from dog pancreas. Highly purified subcellular fractions were prepared from dog pancreas by zonal sucrose-density ultracentrifugation and assayed for their ability to bind 125I-calmodulin in vitro. Proteins contained in these fractions were also examined for binding of 125I-calmodulin after their separation by polyacrylamide-gel electrophoresis in SDS. Calmodulin-binding proteins were detected in all subcellular fractions except the zymogen granule and zymogen-granule membrane fractions. One calmodulin-binding protein (Mr 240,000), observed in a washed smooth-microsomal fraction, has properties similar to those of alpha-fodrin. The postribosomal-supernatant fraction contained three prominent calmodulin-binding proteins, with apparent Mr values of 62,000, 50,000 and 40,000. Calmodulin-binding proteins, prepared from a postmicrosomal-supernatant fraction by Ca2+-dependent affinity chromatography on immobilized calmodulin, exhibited calmodulin-dependent phosphodiesterase, protein phosphatase and protein kinase activities. In the presence of Ca2+ and calmodulin, phosphorylation of smooth-muscle myosin light chain and brain synapsin and autophosphorylation of a Mr-50,000 protein were observed. Analysis of the protein composition of the preparation by SDS/polyacrylamide-gel electrophoresis revealed a major protein of Mr 50,000 which bound 125I-calmodulin. This protein shares characteristics with the calmodulin-dependent multifunctional protein kinase (kinase II) recently observed to have a widespread distribution. The possible role of calmodulin-binding proteins and calmodulin-regulated enzymes in the regulation of exocrine pancreatic protein synthesis and secretion is discussed.

Calcium-activated, calmodulin-dependent protein kinase activity in bovine thyroid cytosol

Bovine thyroid 100,000 X g supernatant contained calcium-activated, calmodulin-dependent protein kinase (PK-CaM) activity. The PK-CaM was partially purified using ion-exchange chromatography and characterized. PK-CaM, using casein as exogenous substrate, was not stimulated by Ca2+(0-500 microM) or calmodulin (1-10 micrograms) by themselves, but was stimulated by the combination of the two by 100%. The activation of the enzyme by Ca2+ and calmodulin was dose-dependent with maximal stimulation evident at 1 microM free-Ca2+ and 3 micrograms calmodulin. Both chlorpromazine and trifluoperazine inhibited the thyroid enzyme in a dose-related manner. The molecular weight (MW) of the PK-CaM, based on gel filtration, was approximately 500,000. PK-CaM could also be demonstrated using endogenous thyroid cytosol proteins as substrate. Separation of these 32P-labelled proteins by SDS-PAGE and subsequent autoradiography revealed that one major protein of approximately 56,000 MW was phosphorylated by PK-CaM. In some experiments, a second, less-intense protein band of approximately 64,000 MW was also phosphorylated. Evidence is presented, suggesting that these two protein bands may result from the autophosphorylation of the PK-CaM holoenzyme. These results offer a molecular mechanism, in addition to protein kinase C, by which Ca2+ effects may be mediated in thyroid.

Calmodulin regulation of the cholinergic receptor in the rat heart during ontogeny and senescence

The contents of calmodulin and cholinergic muscarinic receptor binding sites in the hearts of fetal, adult and aged rats have been examined. A biphasic pattern of calmodulin development was observed. A relatively high level of calmodulin appeared on gestational days 14-15 followed by a steady but significant decrease at birth and during the first week of postnatal life. The level of calmodulin then increased significantly during the first month followed by a decrease at 6 and 26 months of age. Calmodulin contents were significantly higher in the atrium than in the ventricle in the age groups of 1-26 months. The number of [3H]QNB binding sites showed a steady increase during the gestational periods studied, reaching a peak at 9 days after birth and followed by a significant (P less than 0.05) decline at 6 and 26 months of age. A good correlation between the levels of [3H]QNB binding and calmodulin was observed from day 9 of the postnatal period to 26 months of age. In the presence of calcium, calmodulin induced a dose-dependent receptor binding loss in the hearts of postnatal, young adult and aged rats under phosphorylating conditions. These findings support the suggestion that calmodulin may regulate cholinergic functions during ontogeny and senescence.

The mechanism of the effect of K+ on the steroidogenesis of rat zona glomerulosa cells of the adrenal cortex: role of cyclic AMP

The effects of various concentrations of extracellular K+ (3.6-13 mM) on the steroid (corticosterone and aldosterone) and cyclic AMP outputs of capsular cells (95% zona glomerulosa) of the rat adrenal cortex were studied at different concentrations of extracellular Ca2+. Small amounts of EGTA (50 microM) were added to reduce the free Ca2+ concentrations effectively to zero at the lowest possible total Ca2+ concentration. At a total extracellular concentration of 2.5 mM Ca2+, in 27 experiments the mean values of the steroid and cAMP outputs showed a maximum at 8.4 mM K+. The increase in steroid and cAMP outputs at 5.9, 8.4 and 13 mM K+ compared with that at 3.6 mM were highly significant (p less than 0.01). The overall correlation of either corticosterone or aldosterone with cAMP outputs was also highly significant and was even better from 3.6 to 8.4 mM K+. Lowering the effective free concentration of Ca2+ to zero decreased the steroid and cAMP outputs significantly at all K+ concentrations, and no output was then significantly higher than at 3.6 mM. With the pooled data on outputs at all total Ca2+ (2.5, 0.5, 0.25, 0.10, 0.05 and 0.0 mM) and K+ (3.6, 5.9, 8.4 and 13 mM) concentrations, the correlation of either steroid with cAMP outputs was highly significant (but again optimally from 3.6 to 8.4 mM K+). Nifedipine (10(-6) to 10(-4) M) was added to the incubations with the aim of specifically inhibiting Ca2+ influx at total extracellular Ca2+ concentrations of 2.5, 1.25 and 0.25 mM and with the usual K+ concentrations. The cAMP outputs were reduced at all K+ concentrations above 3.6 mM K+. The effect was highly significant at 10(-4) M nifedipine and a total Ca2+ of 1.25 mM, which with the incubation conditions used, corresponds to the free Ca2+ concentrations in vivo. These results indicate that cAMP plays a significant role in the stimulation of steroid output by K+ particularly between 3.6 and 8.4 mM K+. In this range of K+ concentrations the stimulation of cAMP seems to be controlled by increases in Ca2+ influx. The correlation of steroid and cAMP output at the higher K+ concentrations (between 8.4 and 13 mM K) and at the various total Ca2+ concentrations is less significant. Also, with all concentrations of added nifedipine there is an 'anomalous' increase in steroid output at 13 mM K+ and at total Ca2+ concentrations of 2.5 and 1.25 mM. However, at the same K+ concentrations and at 0.25 mM Ca2+, nifedipine decreases steroid outputs.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of calmodulin antagonists on prostaglandin E2-induced responses in rat calvarial bone cells

Osteoclastic (OC) and osteoblastic (OB) cells were isolated by sequential collagenase digestions of new-born rat calvaria. Prostaglandin E2(PGE2) did not alter total calmodulin levels after a 5 or 60 min incubation. The calmodulin antagonists, trifluoperazine (TFP) at 10-50 microM and W-7 (50 microM) inhibited PGE2-induced increases in calcium uptake by OC cells, but had no effect on control OC or OB calcium levels. W-5 (50 microM), a chlorine-deficient analogue of W-7 with weak anti-calmodulin activity, had no effect. Compound 48/80 (100-500 micrograms/ml), a highly effective calmodulin antagonist in other systems, had no effect on PGE2-induced calcium levels or control calcium uptake. There was inhibition of PGE2-induced increases in cyclic AMP by compound 48/80 (100 micrograms/ml) in both OC and OB cells but no effect on control levels. TFP at 50 microM inhibited both control and PGE2-induced increases in cyclic AMP but at 10 microM it lessened only the hormone-induced effect. W-7 (100 microM) inhibited PGE2-induced increases in OC and OB cyclic AMP but had no effect on control levels; W-5 (50 microM) had no effect on either of these. Dibutyryl cyclic AMP had no effect on control calcium uptake, PGE2-induced increases or W-7 inhibition of the PGE-2 effect on calcium uptake. The calmodulin antagonists, at doses which had affected only PGE2-induced increases in calcium uptake and/or cyclic AMP production, had no effect on leucine uptake by OC or OB cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of phenothiazines on phosphate incorporation and chloride uptake in isolated intestinal epithelial cells

Isolated, intact epithelial cells from rat ileum synthesized a variety of radiolabeled compounds when 32Pi was added to the incubation medium. One of these, referred to as P-0.7 because of its Rf value in the thin layer chromatography system used to separate phosphorylated compounds, was found in the extracellular medium but not in extracts of cells. Synthesis of P-0.7 was inhibited by phenothiazines, with an EC50 value of 205 microM for trifluoperazine. Phenothiazines also inhibited uptake into isolated cells, with EC50 values of 288 and 359 microM for trifluoperazine and chlorpromazine, respectively. Effects of the phenothiazines on chloride uptake were not mimicked by the local anesthetic lidocaine (1 mM), the calcium channel blocker verapamil (0.5 mM), SITS or furosemide, or by removal of sodium or calcium from the medium.

Vesicular demyelination induced by raised intracellular calcium

Incubation of nerve with high concentrations of the divalent cation ionophore A23187 produces myelin vesiculation (Schlaepfer 1977). This observation has now been extended using segments of rat ventral or dorsal root incubated with high (19 microM, 10 micrograms/ml) or low (1-1.5 microM) concentrations of A23187, or another divalent ionophore, ionomycin. Low concentrations of A23187 induced no vesiculation within a 2-h period. However, subsequent incubation of these roots in fresh, ionophore-free medium for 20 h, resulted in a prominent vesicular demyelination at the Schmidt-Lanterman incisures and paranodes of many fibres. At this time (22 h) the Schwann cells associated with some demyelinating internodes appeared vital upon ultrastructural examination: the cells also excluded the nuclear dye nigrosin. High concentrations of A23187 induced a similar vesicular demyelination in affected fibres within only 15-20 min. While the Schwann cells continued to exclude nigrosin for a further 4 h, their ultrastructural appearance indicated that they were probably in the early stages of necrosis. Incubation of moribund root with the ionophore produced no myelin vesiculation. At all ionophore concentrations, the myelin vesiculation was dependent upon the presence of extracellular Ca2+, and could be modulated in severity by varying this concentration. Other divalent cations (Ba2+, Co2+, Mg2+, Mn2+, Ni2+, Sr2+) could not substitute for Ca2+. The vesiculation induced by A23187 could be entirely prevented by the addition of Zn2+ (greater than or equal to 1 microM), Ni2+ (greater than or equal to 1-10 microM), Co2+ (greater than or equal to 100 microM) or Mn2+ (greater than or equal to 100 microM) to the bathing medium. A23187 applied to only part of an isolated internode resulted in a localization of the myelin disruption to that region. Ionomycin (greater than or equal to 1 microM), an ionophore with a greater selectivity for Ca2+ than A23187, also induced a prompt Ca2+-dependent myelin vesiculation. We conclude that vesicular demyelination can be initiated in vital Schwann cells by a raised intracellular Ca2+ concentration. Such demyelination does not necessarily lead to Schwann cell death. The possible relevance of the findings to vesicular demyelinating neuropathies is discussed, and a hypothesis regarding the mechanism of demyelination is advanced.

Regulatory effect of calcium on 3H-dopamine binding to guinea-pig heart membrane preparations

The effects of various cations on the specific binding of dopamine to its recognition sites are described using guinea-pig heart membranes as a substrate. Only CaCl2 provoked a dose-dependent facilitatory effect, while KCl, NaCl and MgCl2 acted in the opposite sense. Moreover, Na2EDTA also had an inhibitory effect on dopamine binding and completely prevented the facilitatory action of CaCl2 on 3H-dopamine binding. This effect is partially counteracted by trifluoperazine but unaffected by verapamil. We can conclude from this that calcium seems to be essential to optimizing 3H-dopamine binding to cardiac membrane preparations.

Inhibitory effect of sodium salicylate on ADP-induced platelet aggregation and on 45Ca2+ uptake into platelets

The effects of sodium salicylate (SS) on ADP-induced platelet aggregation and on a metabolism of calcium in platelets were studied, using gel-filtrated platelets (GFP). SS inhibited dose-responsively ADP-induced aggregation in the presence of fibrinogen and Ca2+. It was found that extracellular 45Ca2+ was rapidly taken up into platelets after stimulation by ADP, while SS significantly inhibited this activity. On the other hand, SS had no effect on platelet aggregation induced by 0.11-1.0 microM ionophore A23187. Therefore, it was found that the inhibitory effect of SS on ADP-induced platelet aggregation may be due to the inhibition of the active influx of extracellular Ca2+ into platelets during aggregation.

Calcium and calmodulin in the regulation of human thyroid adenylate cyclase activity

TSH (thyrotropin)-stimulated human thyroid adenylate cyclase has a biphasic response to Ca2+, being activated by submicromolar Ca2+ (optimum 22nM), with inhibition at higher concentrations. Calmodulin antagonists caused an inhibition of TSH-stimulated adenylate cyclase in a dose-dependent manner. Inhibition of TSH-and TSIg-(thyroid-stimulating immunoglobulins)-stimulated activity was more marked than that of basal, NaF- or forskolin-stimulated activity. This inhibition was not due to a decreased binding of TSH to its receptor. Addition of pure calmodulin to particulate preparations of human non-toxic goitre which had not been calmodulin-depleted had no effect on adenylate cyclase activity. EGTA was ineffective in removing calmodulin from particulate preparations, but treatment with the tervalent metal ion La3+ resulted in a loss of up to 98% of calmodulin activity from these preparations. Addition of La3+ directly to the adenylate cyclase assay resulted in a partial inhibition of TSH- and NaF-stimulated activity, with 50% inhibition produced by 5.1 microM and 4.0 microM-La3+ respectively. Particulate preparations with La3+ showed a decrease of TSH- and NaF-stimulated adenylate cyclase activity (approx. 40-60%). In La3+-treated preparations there was a decrease in sensitivity of TSH-stimulated adenylate cyclase to Ca2+ over a wide range of Ca2+ concentrations, but most markedly in the region of the optimal stimulatory Ca2+ concentration. In particulate preparations from which endogenous calmodulin had been removed by La3+ treatment, the addition of pure calmodulin caused an increase (73 +/- 22%; mean +/- S.E.M., n = 8) in TSH-stimulated thyroid adenylate cyclase activity. This was seen in 8 out of 13 experiments.

Calmodulin activation of adenylate cyclase in the mouse B16 melanoma

Calmodulin antagonists inhibited hormone-stimulated cyclic AMP accumulation in both cultured cells and cell lysates of mouse B16 melanoma. Particulate preparations of B16 melanoma contained 34-45% of total cell calmodulin, which could not be dissociated by extensive washing irrespective of the presence of EGTA in the buffer. The adenylate cyclase activity in such preparations was unaffected by the addition of exogenous calmodulin. However, the rare-earth-metal ion La3+, which can mimic or replace Ca2+ in many systems, produced an immediate inhibition of agonist-stimulated adenylate cyclase activity and preincubation of particulate preparations was La3+ followed by washing with La3+-free buffer dissociated calmodulin (96% loss) from particulate preparations. The loss of calmodulin from particulate preparations was associated with a decrease in agonist responsiveness (74%) and a marked change in the Ca2+-sensitivity of the enzyme, low concentrations of calcium (approx. 10 nM) now failing to stimulate enzyme activity, high concentrations of calcium (greater than or equal to 100 nM) producing greater-than-normal inhibition of enzyme activity. Direct activation of adenylate cyclase by the addition of pure calmodulin was now demonstrable in such calmodulin-depleted particulate preparations. Half-maximal stimulation of agonist-responsive adenylate cyclase occurred at 80 nM-calmodulin in the presence of 10 microM free Ca2+. Maximal stimulation by calmodulin (at 300-600 nM) restored enzyme activity to 89 +/- 5% (mean +/- S.E.M., n = 7) of the activity in untreated, calmodulin-intact, preparations.

Improved detection of calcium-binding proteins in polyacrylamide gels

We refined the method of Schibeci and Martonosi (1980a) to enhance detection of calcium-binding proteins in polyacrylamide gels using 45Ca2+. Our efforts have produced a method which is shorter, has 40-fold greater sensitivity over the previous method, and will detect 'EF hand'-containing calcium-binding proteins in polyacrylamide gels below the 0.5 microgram level. In addition, this method will detect at least one example from every described class of calcium-binding protein, including lectins and gamma-carboxyglutamic acid containing calcium-binding proteins. The method should be useful for detecting calcium-binding proteins which may trigger neurotransmitter release.

Studies of the mechanism of noradrenaline stimulation of fluid absorption by rat jejunum in vitro

The everted-sac technique was used to study the mechanism of action of noradrenaline on fluid absorption by rat jejunum. Noradrenaline (10(-3) M) significantly stimulated fluid absorption and this effect was dependent on the presence of calcium ions in the serosal fluid. Strontium, but not magnesium could substitute for calcium. Verapamil, manganese and neodymium, all inhibitors of calcium transport, blocked noradrenaline-stimulated fluid absorption when present in the serosal compartment without any effect on basal or glucose-stimulated absorption. Inhibitors of the translation stage of protein synthesis inhibited the response whereas blocking the transcription stage of protein synthesis was without effect. The noradrenaline response was not attenuated by tetrodotoxin suggesting that the response is not indirect due to noradrenaline altering endogenous intestinal nervous activity. It is concluded that noradrenaline acts by opening calcium channels in the basolateral membranes of epithelial cells, resulting in an influx of calcium which stimulates ribosomal protein synthesis to produce proteins involved in fluid transport.

Adrenal chromaffin cell calmodulin: its subcellular distribution and binding to chromaffin granule membrane proteins

Bovine adrenal medullae were homogenized in the presence or in the absence of EGTA and different subcellular fractions were prepared by differential and density gradient centrifugations. In the presence of the chelating agent, 69% of the total calmodulin, measured by radioimmunoassay, was present in the cytosol; the rest was bound to different membrane-containing fractions (nuclei, microsomal, and crude granule fraction). When the chelating agent was omitted, 43% of the calmodulin was present in the cytosol, the remaining calmodulin being membrane-bound. Further resolution of the crude granule fraction by sucrose density centrifugation demonstrated that the distribution of calmodulin in the density gradient was similar to the distribution of chromaffin granules rather than to that of mitochondria, Golgi elements, and lysosomes. In this case, there was also more calmodulin bound to chromaffin granules when EGTA was omitted from the density gradient. Experiments with 125I-calmodulin indicated the presence of high-affinity binding sites (KD = 1.3 X 10(-8) M; Bmax = 30 pmol/mg protein) for calmodulin in chromaffin granule membranes. Further, photoaffinity crosslinking experiments with 125I-calmodulin followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography indicated the presence of three calmodulin-binding polypeptide complexes (84,000; 41,000; and 38,000 daltons) in chromaffin granule membranes. These polypeptides were not labelled when either Ca2+ was omitted or an excess of nonradioactive calmodulin was present in the photolysis buffer, indicating the Ca2+ dependency and the specificity of the interaction. On the basis of the results described, it is suggested that the cellular levels of Ca2+ control the cellular distribution of calmodulin and its binding to specific chromaffin granule membrane proteins. Further, it is also suggested that the interactions between calmodulin and granule proteins might play a role in stimulus-secretion coupling.

The inhibitory effect of phenothiazines on NK-mediated cytolysis of tumor cells

Non-toxic concentrations of fluphenazine caused a marked (90%) inhibition of NK-mediated cytolysis of YAC-1 tumor cells. The biologically inactive sulphoxide derivative was not inhibitory and the efficacy of inhibition of other compounds was directly correlated (r = -0.96, p less than 0.02) with their reported affinities for calmodulin. Fluphenazine may act on the earliest stages of the target-effector interaction since conjugate formation between CBA effectors and YAC target cells decreased from 20% to 6% (p less than 0.02) upon pre-treatment with fluphenazine. However, fluphenazine was not selective for NK cells since cytotoxic T lymphocytes, derived from both mixed lymphocyte culture and by concanavalin A stimulation, revealed depressed cytolytic activity against P815 tumor targets after fluphenazine treatment. Tumoricidal activity by activated macrophages and effectors of antibody-dependent cell-mediated cytotoxicity was also blocked. Fluphenazine inhibition was reversible, since addition of 1.25-5 micrograms/ml of the calcium ionophore A23187 to fluphenazine-treated effectors restored NK binding and cytolytic functions to normal levels. Calmodulin was isolated from NK-enriched populations by affinity chromatography on sepharose-fluphenazine columns. Pre-treatment of effector cells with [3H]fluphenazine and isolation of calmodulin by immunoprecipitation and SDS-polyacrylamide gel electrophoresis showed that fluphenazine entered the cells and bound a calmodulin-like molecule. These data are compatible with the suggestion that fluphenazine inhibits NK function by inactivating the calcium-calmodulin complex and thereby altering binding events in the target-effector interaction. Other actions of the phenothiazines are also possible.

Calmodulin activation of cyclic AMP phosphodiesterase in the B16 mouse melanoma

Mouse B16 melanoma extracts of both cultured cells and tumour tissue contain cyclic AMP phosphodiesterase activity, with 95% present in the soluble fraction. Although activation of the enzyme by added calmodulin did not occur, it was found that endogenous calmodulin was present at a level sufficient to activate fully the enzyme. The ability of Ca-calmodulin to stimulate cyclic AMP phosphodiesterase in this tissue was shown by the inhibitory effect of N-(6-aminohexyl)-5-chloronaphthalenesulphonamide (W7), a known calmodulin antagonist; by the activation of the enzyme with exogenous calmodulin observed in supernatants depleted of endogenous calmodulin by passage over fluphenazine-Sepharose 6B in the presence of Ca2+; by the Ca-dependent binding of the enzyme to calmodulin-agarose and its activation by Ca-calmodulin after elution from the column with EGTA-containing buffer. It was calculated that about 50% of the total cyclic AMP phosphodiesterase activity was calmodulin-activated in this tissue.

Phenothiazines cause a shift in the cAMP dose-response: selection of resistant variants in a murine thymoma line

Cyclic AMP and glucocorticoid hormones each promote a cytolytic response in the murine lymphoid cell line WEHI-7.1 (W7). The sensitivity to dibutyryl cyclic AMP (dbcAMP), but not dexamethasone, can be enhanced by several psychotropic drugs that have the capacity to interfere with a variety of calcium-regulated functions. We have characterized the response of W7 cells to the phenothiazine trifluoperazine (TFP) and found that TFP concentrations, which decreased the growth rate by twofold, shifted the dose response to dbcAMP approximately tenfold. A similar but smaller shift was seen with the phosphodiesterase inhibitor methylisobutylxanthine (MIX). The effects of TFP and MIX on the dbcAMP response were additive, suggesting that TFP may act to increase the sensitivity of W7 cells to the action of cAMP-dependent protein kinase, and that the increased sensitivity may be due to altered lytic functions coregulated by both cAMP and calcium. The change in the dose response to dbcAMP caused by TFP provided a means of selection to obtain variants that were altered in their capacity to respond to dbcAMP, TFP, or the combination of the two drugs. Eight (out of 36) of the lines that were obtained after a mutagenesis and combined drug selection have been partially characterized. This has revealed the existence of several new phenotypes. Most have an altered response to dbcAMP in the presence of TFP and are likely to represent variants that have not been observed before.

Inhibition of (H+ + K+)-ATPase and H+ accumulation in hog gastric membranes by trifluoperazine, verapamil and 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate

The mechanism of gastric antisecretory action for trifluoperazine, verapamil and 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) has been studied utilizing isolated hog gastric membranes enriched with (H+ + K+)-ATPase. The drugs inhibited the gastric ATPase due to their apparent competition with K+ for the luminal high-affinity K+-site of the ATPase. The dose to inhibit 50% (ID50) of the ATPase in the membranes rendered freely permeable to K+ (20 mM) was 50 microM for trifluoperazine and 1.5 mM for verapamil and TMB-8. In intact hog gastric membranes which develop a pH gradient in the presence of valinomycin, ATP and KCl, however, trifluoperazine at 4 microM, verapamil and TMB-8 at 15 microM inhibited 40 and 30% of the valinomycin-stimulated ATPase activity, respectively, and also blocked the ionophore-dependent intravesicular acidification as measured by aminopyrine accumulation. The enhanced potency of the drugs to inhibit the ATPase in the intact membrane vesicles may be attributed to the accumulation of the drugs as a weak base within the vesicles, where the luminal K+-site of the ATPase is accessible. Calmodulin and Ca2+ had no effect on the extent of H+-accumulation as measured by aminopyrine accumulation in the membrane vesicles which were prepared in the presence of 1 mM EGTA. Since the drugs showed similar potency in interfering with H+ movements either in the membrane vesicles or isolated rabbit gastric glands stimulated by dibutyryl cAMP, it is reasonable to suggest the inhibitory effect of the drugs on (H+ + K+)-ATPase as a primary cause for such interferences in both cases. A trifluoperazine analog and other lipophilic amine drugs similarly inhibited (H+ + K+)-ATPase and H+ accumulation in the membrane vesicles or in the glands. We have concluded that a tertiary amine, the only common functional group among these drugs, is primarily responsible for their ability to interact with the high-affinity K+ site of the gastric ATPase.

Evidence for the presence of calmodulin in fish mucus

Partly purified mucus collected from the skin of three species of fish contains a protein that, on sodium dodecyl sulphate/polyacrylamide gel electrophoresis, comigrates with bovine brain calmodulin and shows the same calcium-dependent shift in electrophoretic mobility as calmodulin. Fish mucus contains a heat-stable activator of cyclic nucleotide phosphodiesterase; activation is concentration dependent and sensitive to the specific calmodulin inhibitor calmidazolium (R 24571). The presence of calmodulin in fish mucus is further indicated by means of a specific radioimmunoassay. A drop in the calcium concentration of the water induces an increase in the immunoassayable calmodulin concentration of mucus, which indicates that the function of calmodulin in mucus is related to control of permeability of the skin epithelium to water and ions.

Pain threshold and morphine activity in vitamin D-deficient rats

In rats, vitamin D-deficiency increases basal pain threshold and the analgesic effect of morphine (hot plate test). Cholecalciferol (1000 I.U./Kg/day s.c.x 5 days) restores pain sensitivity in vitamin D-deficient rats and brings the analgesic effect of morphine back to normal. On the other hand, tolerance to morphine develops faster in vitamin D-deficient rats, this effect too being prevented by cholecalciferol treatment. These data suggest a role for vitamin D status in pain sensitivity and opiate activity.

The nature of the increased sensitivity to injected GTP of the sodium efflux in barnacle muscle fibers pre-exposed to aldosterone

A study has been made of the increased sensitivity to injected GTP of the sodium efflux in barnacle muscle fibers pre-exposed to aldosterone and of the problem whether or not aldosterone acts by raising the internal ATP level. The results indicate that increased sensitivity to injected GTP develops fully some 8 hr following external application of 10(-6) M aldosterone. Neither actinomycin D nor cycloheximide abolishes this extrasensitivity. This is also true of colchicine and cytochalasin B. The magnitude of the sustained response to injected "dialyzed" cholera toxin or cAMP-protein kinase catalytic subunit is practically the same as that of unexposed fibers. Internal ATP levels in pre-exposed fibers are higher than in unexposed fibers, even in the presence of cycloheximide. Injection of ADP (0.1 M) raises the ATP levels and reduces the ArP levels, more so in unexposed fibers. The suggestion is made that extrasensitivity of pre-exposed fibers to injected guanine nucleotides represents a post-translational phenomenon which might involve delay in the reassociation of R2 with C (of cAMP-PK).

Calmodulin during development and metamorphosis in urodelan amphibians

Calmodulin isolated and purified to homogeneity from young larvae is very similar to that obtained from adult Pleurodeles waltlii and these proteins are almost identical to previously described vertebrate calmodulins. During P. waltlii development, an increase in total individual calmodulin content is observed after the heart beating stage. In dorsal axial muscle, calmodulin level which is very high at the beginning of larval life (premetamorphosis) decreases strikingly in the first part of prometamorphosis. Such an evolution is observed in Ambystoma mexicanum too. Then, a significant increase occurs during metamorphosis. In contrast, calmodulin level in P. waltlii cardiac ventricular muscle increases continuously from hatching to the end of metamorphic climax. Thyroxine treatment which promotes precocious metamorphosis in P. waltlii and experimental metamorphosis in neotenic A. mexicanum, induces a rapid and significant increase in muscle calmodulin concentration.