Local anesthetics, mepacrine, and propranolol are antagonists of calmodulin

High-throughput screening of TRPV1 ligands in the light of the Bioluminescence Resonance Energy Transfer technique

Ion channels are attractive drug targets for many therapeutic applications. However, high-throughput screening (HTS) of drug candidates is difficult and remains very expensive. We thus assessed the suitability of the Bioluminescence Resonance Energy Transfer (BRET) technique as a new HTS method for ion-channel studies by taking advantage of our recently characterized intra- and intermolecular BRET probes targeting the TRPV1 ion channel. These BRET probes monitor conformational changes during TRPV1 gating and subsequent coupling with Calmodulin, two molecular events that are intractable using reference techniques such as automated calcium assay (ACA) and automated patch-clamp (APC). We screened the small-sized Prestwick chemical library, encompassing 1200 compounds with high structural diversity, using either intra- and intermolecular BRET probes or ACA. Secondary screening of the detected hits was done using APC. Multiparametric analysis of our results shed light on the capability of calmodulin inhibitors included in the Prestwick library to inhibit TRPV1 activation by Capsaicin (CAPS). BRET was the lead technique for this identification process. Finally, we present data exemplifying the use of intramolecular BRET probes to study other TRPs and non-TRPs ion channels. Knowing the ease of use of BRET biosensors and the low cost of the BRET technique, these assays may advantageously be included for extending ion-channel drug screening. Significance Statement We screened a chemical library against TRPV1 ion channel using Bioluminescence Resonance Energy Transfer (BRET) molecular probes, and compared the results with the ones obtained using reference techniques such as automated calcium assay and automated patch-clamp. Multiparametric analysis of our results shed light on the capability of Calmodulin antagonists to inhibit chemical activation of TRPV1, and indicates that BRET probes may advantageously be included in ion channel drug screening campaigns.

Antimalarial Quinacrine and Chloroquine Lose Their Activity by Decreasing Cationic Amphiphilic Structure with a Slight Decrease in pH

Quinacrine (QC) and chloroquine (CQ) have antimicrobial and antiviral activities as well as antimalarial activity, although the mechanisms remain unknown. QC increased the antimicrobial activity against yeast exponentially with a pH-dependent increase in the cationic amphiphilic drug (CAD) structure. CAD-QC localized in the yeast membranes and induced glucose starvation by noncompetitively inhibiting glucose uptake as antipsychotic chlorpromazine (CPZ) did. An exponential increase in antimicrobial activity with pH-dependent CAD formation was also observed for CQ, indicating that the CAD structure is crucial for its pharmacological activity. A decrease in CAD structure with a slight decrease in pH from 7.4 greatly reduced their effects; namely, these drugs would inefficiently act on falciparum malaria and COVID-19 pneumonia patients with acidosis, resulting in resistance. The decrease in CAD structure at physiological pH was not observed for quinine, primaquine, or mefloquine. Therefore, restoring the normal blood pH or using pH-insensitive quinoline drugs might be effective for these infectious diseases with acidosis.

Effects of 39 Compounds on Calmodulin-Regulated Adenylyl Cyclases AC1 and Bacillus anthracis Edema Factor

Adenylyl cyclases (ACs) catalyze the conversion of ATP into the second messenger cAMP. Membranous AC1 (AC1) is involved in processes of memory and learning and in muscle pain. The AC toxin edema factor (EF) of Bacillus anthracis is involved in the development of anthrax. Both ACs are stimulated by the eukaryotic Ca²⁺-sensor calmodulin (CaM). The CaM-AC interaction could constitute a potential target to enhance or impair the AC activity of AC1 and EF to intervene in above (patho)physiological mechanisms. Thus, we analyzed the impact of 39 compounds including typical CaM-inhibitors, an anticonvulsant, an anticholinergic, antidepressants, antipsychotics and Ca²⁺-antagonists on CaM-stimulated catalytic activity of AC1 and EF. Compounds were tested at 10 μM, i.e., a concentration that can be reached therapeutically for certain antidepressants and antipsychotics. Calmidazolium chloride decreased CaM-stimulated AC1 activity moderately by about 30%. In contrast, CaM-stimulated EF activity was abrogated by calmidazolium chloride and additionally decreased by chlorpromazine, felodipine, penfluridol and trifluoperazine by about 20–40%. The activity of both ACs was decreased by calmidazolium chloride in the presence and absence of CaM. Thus, CaM-stimulated AC1 activity is more insensitive to inhibition by small molecules than CaM-stimulated EF activity. Inhibition of AC1 and EF by calmidazolium chloride is largely mediated via a CaM-independent allosteric mechanism.

Pheromone interactions and ionic communication in gametes of aquatic fungusAllomyces macrogynus

The flagellate male and female gametes of the aquatic fungusAllomyces macrogynus are each attracted to a sexual pheromone produced by the opposite gamete type. The sperm attractant, sirenin, causes chemotaxis to female gametes. Examination of sperm chemotaxis shows that the pheromone influences the frequency of directional changes and the duration of a chemotactic run. Physiological experiments using tertiary amine local anesthetics or calcium chelators such as EGTA demonstrate that sirenin stimulates the influx of calcium ions (Ca(2+)) into the sperm cytoplasm. Radiological experiments with(45)CaCl2 have demonstrated this calcium flux directly. Structurally, sirenin is an oxygenated sesquiterpene that consists of a cyclopropyl ring attached onto an isohexenyl side chain. The pheromone displays a threshold concentration for attraction at 10 pM in chemotaxis bioassays. Structure-activity relationships with racemic sirenin and sirenin analogs indicate that biological activity requires a terminal hydroxymethyl group on the side chain. In addition, a hydrophobic group must be present at the other end of the sirenin molecule. Besides sirenin, the sperm cells ofA. macrogynus produce a female attractant, parisin. While the molecular nature of this attractant is not completely resolved, some general features of the molecule suggest it may be similar structurally to sirenin.

Modulation of morphogenesis in Candida albicans by various small molecules

The pathogenic yeast Candida albicans, a member of the mucosal microbiota, is responsible for a large spectrum of infections, ranging from benign thrush and vulvovaginitis in both healthy and immunocompromised individuals to severe, life-threatening infections in immunocompromised patients. A striking feature of C. albicans is its ability to grow as budding yeast and as filamentous forms, including hyphae and pseudohyphae. The yeast-to-hypha transition contributes to the overall virulence of C. albicans and may even constitute a target for the development of antifungal drugs. Indeed, impairing morphogenesis in C. albicans has been shown to be a means to treat candidiasis. Additionally, a large number of small molecules such as farnesol, fatty acids, rapamycin, geldanamycin, histone deacetylase inhibitors, and cell cycle inhibitors have been reported to modulate the yeast-to-hypha transition in C. albicans. In this minireview, we take a look at molecules that modulate morphogenesis in this pathogenic yeast. When possible, we address experimental findings regarding their mechanisms of action and their therapeutic potential. We discuss whether or not modulating morphogenesis constitutes a strategy to treat Candida infections.

New hopes from old drugs: revisiting DNA-binding small molecules as anticancer agents

Most of the anticancer chemotherapeutic drugs that are broadly and successfully used today are DNA-damaging agents. Targeting of DNA has been proven to cause relatively potent and selective destruction of tumor cells. However, the clinical potential of DNA-damaging agents is limited by the adverse side effects and increased risk of secondary cancers that are consequences of the agents' genotoxicity. In this review, we present evidence that those agents capable of targeting DNA without inducing DNA damage would not be limited in these ways, and may be as potent as DNA-damaging agents in the killing of tumor cells. We use as an example literature data and our own research of the well-known antimalarial drug quinacrine, which binds to DNA without inducing DNA damage, yet modulates a number of cellular pathways that impact tumor cell survival.

Calcium-Stimulated Protein Phosphorylation in Synaptic Membranes

Synaptic membranes from rat brain contain several calcium-requiring protein kinase (PK) activities with different substrate specificities: (a) an activity (CaH-PK) effective at high concentrations of Ca2+ ion in the absence of Mg2+ (active on class F substrates); (b) a (Ca + Mg)-PK activity that is mediated by Ca2+ ion in the presence of Mg2+ (active on class B substrates); (c) (Ca-CaM)-PK activities that exhibit simultaneous requirements for both Ca2+ ion and CaM (for class C and D substrates). Also described are three activities (d-f) that do not require Ca2+ ion: (d) a Mg-PK activity in which the presence of Ca2+ causes the inhibition of phosphorylation (active on class A substrates); (e) an activity affecting a diverse group of substrates (class E substrates), the phosphorylation of which occurs in the presence of Mg2+ ion alone (Mg-PK activity) and is unaffected by the addition of Ca2+ ion and CaM, the substrates of which show different responses to several types of inhibitors; and, finally, (f) the previously well characterized cAMP-dependent PK activities. Several of the substrates of these kinases have been identified in a fairly unambiguous manner: among them are P43 (class A), as the alpha subunit of pyruvate dehydrogenase; P54 (class B), as the presynaptic protein B50; and the doublet P75-P80, as proteins IA and IB of Ueda and Greengard. The most interesting activity is that requiring both Ca2+ and CaM. The half-maximal stimulation (K0.5) for Ca2+ in the presence of CaM was found to be 1.0 microM Ca2+F in untreated membranes. There is little change in this value on prior EGTA extraction of the membranes, which removes the bulk of its Ca2+ and reduces its residual CaM by greater than or equal to 50%. The apparent K0.5 for CaM in the presence of excess Ca2+ ion was found to equal 0.4 microgram per reaction mixture (8 micrograms/ml) or 1.35 micrograms per reaction mixture (27 micrograms/ml), for the untreated and EGTA-treated membranes, respectively.

Cyclic nucleotide phosphodiesterases as targets for treatment of haematological malignancies

The cAMP signalling pathway has emerged as a key regulator of haematopoietic cell proliferation, differentiation and apoptosis. In parallel, general understanding of the biology of cyclic nucleotide PDEs (phosphodiesterases) has advanced considerably, revealing the remarkable complexity of this enzyme system that regulates the amplitude, kinetics and location of intracellular cAMP-mediated signalling. The development of therapeutic inhibitors of specific PDE gene families has resulted in a growing appreciation of the potential therapeutic application of PDE inhibitors to the treatment of immune-mediated illnesses and haematopoietic malignancies. This review summarizes the expression and function of PDEs in normal haematopoietic cells and the evidence that family-specific inhibitors will be therapeutically useful in myeloid and lymphoid malignancies.

Changes in cyclic nucleotide phosphodiesterase activity and calmodulin concentration in heart muscle of cardiomyopathic hamsters

Cyclic nucleotides (cAMP and cGMP) phosphodiesterase (PDE) activities and expression are altered in the cardiac muscle of cardiomyopathic heart failure, and PDE inhibitors improve the abnormal muscle condition through changing the cyclic nucleotide concentration. These observations prompted us to investigate the role of calmodulin (CaM) in the regulation of cyclic nucleotide PDE activities, and moreover to study the modulation of the PDE isozymes in heart failure, using cardiac muscles of cardiomyopathic hamster. The CaM concentrations in the heart muscle of the normal control and cardiomyopathic hamsters (each of three to four hamsters) varied with cell fraction and with the age of the animal. The CaM concentrations in the soluble fraction obtained from cardiomyopathic hamster tissue were significantly increased at 25 and 32 weeks of age (2.02 +/- 0.62 microg/mg protein (mean +/- S.E.), and 3.21 +/- 0.95) compared with that obtained from the control (0.60 +/- 0.04) or cardiomyopathic (0.95 +/- 0.12) hamsters at 8 weeks of age. The solubilized PDE isolated from the hamster heart muscle (three or four hamsters in each age) by column chromatography on diethylaminoethyl (DEAE)-cellulose revealed three peaks of activity, which may correspond to the isozymes of PDE classified recently, namely PDE I, II, and III. These three peaks of activity, particularly peak III, seen in the soluble fraction of cardiomyopathic hamster heart declined in proportion to the age of the animal compared with that of the control hamster heart. In the cGMP-PDE assay system, the concentration of CaM inhibitor W-7 required for 50% inhibition (IC(50)) of PDE I, II, and III peak activities was 140, 29, and 46 microM, respectively, suggesting that PDE II is more sensitive to W-7. These results suggest that alteration in these isozyme activities accompanied with changes of CaM concentration may influence the cardiac muscle contractility in cardiomyopathic hamster via changes of cyclic nucleotide concentration.

Carane derivative stereoisomers of different local anaesthetic and antiplatelet activity similarly potentiate forskolin-stimulated cyclic AMP response and bind to beta-adrenoceptors in the rat brain cortex

A carane derivative, KP-23 [RS](-)-4-(2-hydroxy-3)N-isopropylamino)-propoxyimino)-cis-carane, was earlier described as a potential local anaesthetic and antiplatelet agent, and the following studies revealed that its R and S stereoisomers, KP-23R and KP-23S, have different potencies in the infiltration anaesthesia and platelet aggregation tests. The effects of these stereoisomers on the cyclic AMP (cAMP) generating system and the displacement of [(3)H]CGP 12177 (a beta-adrenoceptor ligand) from its binding sites in the rat cerebral cortical tissue were investigated. The stereoisomers did not affect the basal cAMP level, but, at concentrations between 10(-4) and 10(-3) M, they elevated the forskolin-induced accumulation of cAMP with similar potency. The compounds displaced [(3)H]CGP 12177, however the stereoisomer R was less potent than the racemic KP-23 and the S form (K(i) = 64.1 +/- 5.9 nM, 161.1 +/- 10 nM and 62.1 +/- 5.6 nM for KP-23, KP-23R and KP-23S, respectively). The fact that the stereoisomers differed in both tests only slightly, if at all, suggests that their pharmacological effects are not related to the action on the beta-adrenoceptor/adenylate cyclase system.

Regional anaesthesia, local anaesthetics and the surgical stress response

Epidural anaesthesia has the potential to improve patients' outcome after major surgical procedures by reducing postoperative morbidity and duration of recovery. Possible benefits include the attenuation of cardiac complications, an earlier return of gastrointestinal function associated with an increase in patients' comfort overall, decreased incidence of pulmonary dysfunction, beneficial effects on the coagulation system and a reduction in the inflammatory response. The underlying mechanisms, however, remain unclear. Since local anaesthetics (LAs), reabsorbed from the epidural space, seem to contribute to these effects, it is not easy to differentiate between the systemic effects of LAs and the effects of neuraxial blockade by epidural anaesthesia. Thus, in patients not able or willing to receive intra- and/or postoperative epidural analgesia, systemic administration of LAs may be considered to be a new therapeutic approach for the prevention of postoperative disorders by modulation of the peri- and postoperative inflammatory.

Investigation of photosensitizing dyes for pathogen reduction in red cell suspensions

Despite recent advances in blood safety by careful donor selection and implementation of infectious disease testing, transmission of viruses, bacteria and parasites by transfusion can still rarely occur. One approach to reduce the residual risk from currently tested pathogens and to protect against the emergence of new ones is to investigate methods for pathogen inactivation. The use of photosensitizing dyes for pathogen inactivation has been studied in both red cell and platelet blood components. Optimal properties of sensitizing dyes for use in red cell suspensions include selection of dyes that traverse cell and viral membranes, bind to nucleic acids, absorb light in the red region of the spectrum, inactivate a wide range of pathogens, produce little red cell photodamage from dye not bound to nucleic acid and do not hemolyze red cells in the dark. Early research at the American Red Cross focused on the use of a class of dyes with rigid structures, such as the phenothiazine dyes, beginning with the prototypical sensitizer methylene blue. Results revealed that methylene blue phototreatment could inactivate extracellular virus, but resulted in undesirable defects in the red cell membrane that resulted in enhanced hemolysis that became evident during extended refrigerated blood storage. In addition, methylene blue phototreatment could neither inactivate intracellular viruses nor appreciably inactivate bacteria under conditions of extracellualar viral killing. Attempts to improve intracellular viral inactivation led to the investigations of more hydrophobic phenothiazines, such as methylene violet or dimethylmethylene blue. Although these dyes could inactivate intracellular virus, problems with increased red cell membrane damage and hemolysis persisted or increased. Further studies using red cell additive storage solutions containing high levels of the impermeable ion, citrate, to protect against colloidal osmotic hemolysis as well as competitive inhibitors to limit sensitizer binding to red cell membranes revealed that photoinduced hemolysis stemmed from dye bound to the red cell membrane as well as dye free in solution. Use of red cell additive solutions to prevent colloidal-osmotic hemolysis and use of novel flexible dyes that only act as sensitizers when bound to their targets are two techniques that currently are under investigation for reducing red cell damage. Ultimately, the decision to implement a photodynamic method for pathogen reduction will be determined by weighing the risks of unintended adverse consequences of the procedure itself, such as the potential for genotoxicity and allergic reactions, against the cost and benefits of its implementation.

Quinacrine enhances vesicular stomatitis virus inactivation and diminishes hemolysis of dimethylmethylene blue-phototreated red cells

Several photodynamic methods for virus inactivation in red blood cell (RBC) suspensions have resulted in unwanted hemolysis during extended 1-6 degrees C storage. To explore the possibility that hemolysis may be mediated by a membrane-bound dye, a molecule similar in structure to yet different in light absorption properties from the photosensitizer was used as an inhibitor for RBC membrane binding in virus photoinactivation and photohemolysis studies. The addition of 500 pM quinacrine to oxygenated RBC before treatment with 3.6 microM dimethylmethylene blue (DMMB) and 219 mJ/cm2 red light resulted in an increased extracellular concentration of the sensitizer, increased extracelluar viral inactivation kinetics, and decreased hemolysis during 1-6 degrees C storage without alteration of quinacrine absorption properties. These results collectively suggest that despite its recognized affinity for viral nucleic acid, DMMB also binds to RBC membranes and that the bound dye is, in part, responsible for photoinduced hemolysis.

Comparison of Fonsecaea pedrosoi sclerotic cells obtained in vivo and in vitro: ultrastructure and antigenicity

The parasitic form of Fonsecaea pedrosoi from the hyperkeratotic layer of the skin was obtained from four patients with chromoblastomycosis. Primary cultures containing hyphae and conidia were successfully converted into sclerotic cells in the presence of 800 microM propranolol and low pH as described before. The morphology of sclerotic cells of F. pedrosoi obtained in vivo and in vitro was analyzed by light and electron microscopy. Their antigenicity was also compared by immunofluorescence microscopy and ELISA assays, using serum samples from untreated patients infected with F. pedrosoi. Due to the similarity of the sclerotic cells obtained in vivo and in vitro, the latter can be more adequately in studies of host-parasite interactions in chromoblastomycosis.

Evidence against the involvement of cytochrome P450 metabolites in endothelium-dependent hyperpolarization of the rat main mesenteric artery

1. The influence of different inhibitors of cytochrome P450 mono-oxygenase on the endothelium-dependent and -independent hyperpolarization in the isolated rat main mesenteric artery was investigated. 2. Application of acetylcholine (ACh; 1 microM) for 10 min evoked an endothelium-dependent peak hyperpolarization of about 18 mV followed by a partial recovery to a level 7 mV more negative than the resting value (-50.2 +/- 0.5 mV). 3. Proadifen (30 microM) completely and reversibly inhibited the ACh-induced hyperpolarization. Conversely, the imidazole antimycotics clotrimazole (30 microM) and miconazole (100 microM) had less effect on the peak endothelium-dependent hyperpolarization. The suicide substrate inhibitors 17-octadecynoic acid (17-ODYA; 5 microM) and 1-aminobenzotriazole (1-ABT; 2 mM) did not significantly influence endothelium-dependent hyperpolarization. 4. The endothelium-independent hyperpolarization (16 mV) evoked by leveromakalim (300 nM) was completely inhibited by proadifen as well as by clotrimazole and miconazole but was not affected by 17-ODYA or 1-ABT. 5. These results do not support the view that the ACh-induced endothelium-dependent hyperpolarization in the rat mesenteric artery is mediated by cytochrome P450 mono-oxygenase metabolites. Proadifen and imidazole antimycotics impair the activation of ATP-regulated K+ channels in mesenteric artery cells, rendering non-specific inhibition of smooth muscle K+ channel activation an alternative explanation for the inhibitory influence of some (but not all) P450 inhibitors on endothelium-dependent hyperpolarization in this preparation.

Quinacrine attenuates cyclosporine-induced nephrotoxicity in rats

The biochemical mechanism underlying cyclosporine (CsA)* induced nephrotoxicity is far from clear. Increased generation of oxygen derived free radicals (ODFR) and enhanced activity of phospholipase A2 (PLA2) have been observed in experimental animals following treatment with CsA. Several recent reports have shown that quinacrine, besides being a potent inhibitor of PLA2, suppresses the generation of ODFR. The present study was designed to investigate the effect of quinacrine on CsA induced nephrotoxicity in rats. Male Wistar rats (weighing 280-300 g) were randomized into eight groups of eight animals each. Group 1 (control) received appropriate vehicles only, whereas the rats in groups 2, 3, 4, and 5 received subcutaneous injection of CsA (17.5 mg/kg dissolved in olive oil) daily for 8 weeks. The animals in groups 3, 4, and 5 were also given intraperitoneal injections of quinacrine in three different doses of 2.5 mg/kg, 5 mg/kg, and 10 mg/kg body weight, respectively, in addition to CsA. The animals in groups 6, 7, and 8 received intraperitoneal injection of quinacrine alone at doses of 2.5 mg/kg, 5 mg/kg, and 10 mg/kg respectively for eight weeks. After 8 weeks, animals were sacrificed under light ether anesthesia and blood and kidney samples were collected for various biochemical and histological studies. The biochemical parameters included blood urea nitrogen (BUN), serum creatinine (Scr), potassium, and sodium. The blood was also analyzed for the level of CsA. The kidney samples were analyzed for malondialdehyde (MDA), glutathione, and vitamin E (VE). Kidney sections were prepared for histopathological studies using hematoxylin-eosin staining. There was an increase in BUN, Scr, and potassium levels and decrease in sodium levels in cyclosporine alone treated group, suggesting a significant nephrotoxicity. Quinacrine treatment significantly protected animals against CsA induced biochemical changes. Our studies on free radical indices showed that quinacrine treatment protected animals against cyclosporine induced increase in MDA and depletion of glutathione and VE. The beneficial effect of quinacrine against CsA induced nephrotoxicity was also confirmed by histological studies.

Mildly oxidized LDL induces platelet aggregation through activation of phospholipase A2

Native LDL and LDL oxidized under various conditions were compared in terms of their ability to activate platelets. Native LDL did not induce platelet shape change or aggregation, even at high concentrations (2 mg protein/mL). LDL was mildly oxidized with either CuSO4 (mox-LDL) or 3-(N-morpholino)sydnonimine (SIN-1-LDL). Analysis of mox-LDL and SIN-1-LDL showed a small increase of dienes (E234nm from 0.28 +/- 0.04 to 0.55 +/- 0.09, mean +/- SD) and thiobarbituric acid-reactive substance (from 0 to 10.6 +/- 1.5 nmol/mg, mean +/- SEM), no change in apo B electrophoretic mobility, and a minor (12% to 30%) decrease in polyunsaturated fatty acid content. Interestingly, this small oxidative modification of LDL dramatically changed its effect on platelets. Irreversible aggregation and secretion were induced by a threshold concentration of 0.4 mg protein/mL. In contrast, LDL thoroughly oxidized with CuSO4 (ox-LDL) did not aggregate platelets. Although mox-LDL was depleted in antioxidants (alpha- and gamma-tocopherol, alpha- and beta-carotene, and other carotenoids), incubation of mox-LDL with exogenous alpha-tocopherol did not reverse its ability to induce platelet aggregation and secretion. Preincubation of platelets with the cyclooxygenase inhibitor aspirin or the phospholipase A2 inhibitors trifluoperazine, quinacrine, 4-bromophenacyl bromide, and propranolol completely prevented platelet aggregation and secretion caused by mox-LDL or SIN-1-LDL. These results indicate that mildly oxidized LDL activates platelets through a phospholipase A2/cyclooxygenase-dependent pathway. The complete inhibition of mox-LDL-induced platelet aggregation by aspirin could contribute to its beneficial effect in cardiovascular disease.

Mechanism for procaine-mediated hyperactivated motility in guinea pig spermatozoa

Hyperactivated motility was studied in guinea pig spermatozoa. In the presence of the local anesthetic procaine, a high number of sperm cells (64%) showed hyperactivation when incubated in minimal culture medium with pyruvate, lactate, and glucose. Hyperactivated motility was dependent on glucose in the medium. Sperm ATP concentration was increased twofold in hyperactivated sperm when compared to procaine-treated non-hyperactivated cells. cAMP levels were also higher in hyperactivated cells than in control spermatozoa. Thus, in living spermatozoa high levels of ATP appear to be needed to generate hyperactivation. cAMP is present at a high concentration in hyperactivated spermatozoa, therefore a role of cAMP in hyperactivation cannot be excluded. Depletion of external Ca2+ did not inhibit procaine-induced hyperactivated motility. Hence, procaine canceled the requirement of external Ca2+ for sperm to express hyperactivated motility.

Pharmacological evidence for the involvement of calcium/calmodulin in serotonin 5-HT3 receptor-mediated cation permeability in NG 108-15 cells

In NG 108-15 clonal cells, extracellular application of micromolar concentrations of serotonin [5-hydroxytryptamine (5-HT)] and substance P induces the opening of a cation permeability monitored by the influx of [14C]-guanidinium. The serotoninergic component of this cation permeability is linked to 5-HT3 receptor activation, whereas the substance P component probably involves an "N-terminal-dependent substance P receptor." In this study, [14C]guanidinium influx triggered by 1 microM 5-HT plus 10 microM substance P was shown to be insensitive to tetrodotoxin, verapamil, diltiazem, nimodipine, and omega-conotoxin, as expected from a process independent of voltage-sensitive sodium and calcium channels. In contrast, [14C]guanidinium influx was inhibited by millimolar concentrations of extracellular calcium and by the chelation of intracellular calcium by bis-O-aminophenoxyethanetetraacetic acid. The inhibition by extracellular calcium apparently involved a competition between the divalent cation and [14C]guanidinium for the same channel. When NG 108-15 cells were exposed to X537A, an ionophore that specifically induces release of calcium from intracellular stores, [14C]guanidinium uptake was markedly increased even in the absence of 5-HT and/or substance P. Conversely, [14C]guanidinium influx due to the latter substances could be reversibly and dose-dependently blocked by various drugs that possess calmodulin-antagonizing properties. These results strongly suggest that the cation permeability opened by 5-HT and substance P in NG 108-15 cells involves a calcium/calmodulin-dependent process.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium regulates in vitro dimorphism in chromoblastomycotic fungi

Cladosporium carrionii, Fonsecaea pedrosoi and Phialophora verrucosa, the three most important agents of chromoblastomycosis, produced large numbers of sclerotic bodies at 25 degrees C, and greater numbers at 37 degrees C, after inoculation into a defined pH 2.5 medium containing 0.1 mmol l-1 Ca2+. Higher concentrations of Ca2+ reversed this tendency and promoted maintenance of hyphal growth. Addition of the Ca2+ chelator EGTA to the same medium buffered at pH 6.5 also induced sclerotic bodies, but in a more concentration-dependent fashion. EGTA at 0.5-1.0 mmol l-1 induced maximum numbers of sclerotic bodies in Cl. carrionii, whereas 2 and 8 mmol l-1 concentrations were required for the same results with F. pedrosoi and P. verrucosa, respectively. These findings suggest that Ca2+ concentrations in human tissue may play a paramount role in the dimorphic switching between hyphae and sclerotic bodies among chromoblastomycotic agents during infection.

Antimalarial drugs inhibit calcium-dependent backward swimming and calcium currents in Paramecium calkinsi

The antimalarial drugs, quinacrine, chloroquine, quinine, primaquine, and mefloquine, share structural similarities with W-7, a compound that inhibits calcium-dependent backward swimming and calcium currents in Paramecium. Therefore, we tested whether antimalarial drugs also inhibit backward swimming and calcium currents in P. calkinsi. When the Paramecium is depolarized in high potassium medium, voltage-dependent calcium channels in the ciliary membrane open causing the cell to swim backward for 30 to 70 s. Application of calcium channel inhibitors, such as W-7, reduce the duration of backward swimming. In 0.05 mM calcium, quinacrine, mefloquine, quinine, chloroquine, primaquine and W-7 all reduced the duration of backward swimming. These effects were seen in sodium-containing and sodium-free high potassium solutions as well as sodium-free depolarizing solutions containing potassium channel blockers. In these low calcium solutions, backward swimming was inhibited by 50% at concentrations ranging from 100 nM to 30 microM. At higher calcium concentrations (1 mM or 15 mM), the effects of the antimalarials and W-7 were reduced. The effects of quinacrine and W-7 were tested directly on calcium currents using the two microelectrode voltage clamp technique. In 15 mM calcium, 100 microM quinacrine and 100 microM W-7 reduced the peak calcium current by 51% and 42%, respectively. Thus, antimalarial drugs reduce calcium currents in Paramecium calkinsi.

Blockade by antiarrhythmic drugs of glibenclamide-sensitive K+ channels in Xenopus oocytes

1. The outward K+ current induced by KRN2391 (K+ channel opener) in Xenopus oocytes is blocked by glibenclamide. We have investigated the effects of various classes (I-IV) of antiarrhythmic drugs on this KRN2391-induced response. 2. All class I antiarrhythmic drugs (Na+ channel blockers) tested concentration-dependently suppressed KRN2391-induced responses with the rank order of potency (IC50 in microM), disopyramide (17.8) > aprindine (29.5) > propafenone (63.1) > ajmaline (145) > quinidine (151). Flecainide, SUN1165, lignocaine, mexiletine and procainamide were much less potent (IC50, 450- > 1000 microM) than quinidine. 3. The class II antiarrhythmic drugs (beta-blockers), timolol, (-)- and (+/-)- propranolol, and (+)- propranolol (a non-beta-blocker) inhibited KRN2391-induced K+ currents in a concentration-dependent manner with values for IC50 (microM) of 79, 131, 151 and 129, respectively, whilst butoxamine, oxprenolol, alprenolol, pindolol, nadolol, metoprolol and acebutolol were either weak (IC50, 300 microM-600 microM) or virtually inactive (IC50, > 1000 microM). 4. The class III antiarrhythmic drugs, amiodarone and (+)-sotalol scarcely affected KRN2391 responses. 5. All class IV drugs (Ca2+ antagonists) tested suppressed KRN2391-induced responses in a concentration-dependent manner with an IC50 of 6.3 microM for bepridil, 38 microM for prenylamine, 85 microM for verapamil and 135 microM for diltiazem. 6. In conclusion, antiarrhythmic drugs of classes I, II and IV potently blocked glibenclamide-sensitive K+ channels in Xenopus oocytes.

Modulation of calcium fluxes across synaptosomal plasma membrane by local anesthetics

We have studied the effects of local anesthetics (dibucaine, tetracaine, lidocaine, and procaine) on calcium fluxes through the plasma membrane of synaptosomes. All these local anesthetics inhibit the ATP-dependent calcium uptake by inverted plasma membrane vesicles at concentrations close to those that promote an effective blockade of the action potential. The values obtained for the K0.5 of inhibition of calcium uptake are the following: 23 microM (dibucaine), 0.44 mM (lidocaine), 1.5 mM (procaine), and 0.8 mM (tetracaine). There is a good correlation between these K0.5 values and the concentrations of the local anesthetics that inhibit the Ca2(+)-dependent Mg2(+)-ATPase of these membranes. In addition, except for procaine, these local anesthetics stimulate severalfold the Ca2+ outflow via the Na+/Ca2+ exchange in these membranes. This effect, however, is observed at concentrations slightly higher than those that effectively inhibit the ATP-dependent Ca2+ uptake, e.g., 80-700 microM dibucaine, 2-10 mM lidocaine, and 1-3 mM tetracaine. The results suggest that the Ca2+ buffering of neuronal cytosol is altered by these anesthetics at pharmacological concentrations.

Evidence for an increased sensitivity to Ca2+ in the flagella of sperm from tw32/+mice

The majority of sperm from mice carrying the tw32 haplotype undergo hyperactivation sooner than sperm from +/+ mice of the same strains (Olds-Clarke, Dev Biol 131:475-482, 1989). To investigate the mechanism underlying this abnormal motility, the Ca2+ sensitivity of their flagellar apparatus was compared to that of age- and strain-matched controls using Triton X-100-extracted sperm. Under these conditions, the curvature of the sperm flagellum is controlled by the free calcium concentration. Sperm from mice carrying the tw32 haplotype consistently exhibited a change in flagellar curvature at lower free calcium concentrations than controls. In addition, intact sperm from tw32/+ mice were much more likely than congenic control sperm to have a hook-like bend in the midpiece, which persisted throughout most of the beat cycle. Sperm exhibiting the hooked middle piece could be converted to a more normal appearance by 2 mM procaine, which immobilizes cytoplasmic calcium. Thus an increased sensitivity of the sperm motor apparatus to calcium could be the cause of the precocious hyperactivation of sperm from mice carrying the tw32 haplotype.

Calmodulin dependence of transferrin receptor recycling in rat reticulocytes

Kinetic analysis of transferrin receptor properties in 6-8 day rat reticulocytes showed the existence of a single class of high-affinity receptors (Kd 3-10 nM), of which 20-25% were located at the cell surface and the remainder within an intracellular pool. Total transferrin receptor cycling time was 3.9 min. These studies examined the effects of various inhibitors on receptor-mediated transferrin iron delivery in order to define critical steps and events necessary to maintain the functional integrity of the pathway. Dansylcadaverine inhibited iron uptake by blocking exocytic release of transferrin and return of receptors to the cell surface, but did not affect transferrin endocytosis; this action served to deplete the surface pool of transferrin receptors, leading to shutdown of iron uptake. Calmidazolium and other putative calmodulin antagonists exerted an identical action on iron uptake and receptor recycling. The inhibitory effects of these agents on receptor recycling were overcome by the timely addition of Ca2+/ionomycin. From correlative analyses of the effects of these and other inhibitors, it was concluded that: (1) dansylcadaverine and calmodulin antagonists inhibit iron uptake by suppression of receptor recycling and exocytic transferrin release, (2) protein kinase C, transglutaminase, protein synthesis and release of transferrin-bound iron are not necessary for the functional integrity of the iron delivery pathway, (3) exocytic transferrin release and concomitant receptor recycling in rat reticulocytes is dependent upon Ca2+/calmodulin, (4) dansylcadaverine, dimethyldansylcadaverine and calmidazolium act on iron uptake by interfering with calmodulin function, and (5) the endocytotic and exocytotic arms of the iron delivery pathway are under separate regulatory control.

Association between inhibition of arachidonic acid release and prevention of calcium loading during ATP depletion in cultured rat cardiac myocytes

The development of irreversible myocardial ischemic injury is associated with progressive degradation of membrane phospholipids, accumulation of arachidonate and other free fatty acids, and electrolyte derangements, including calcium accumulation. To study the relationship between arachidonate release and calcium loading during adenosine triphosphate (ATP) depletion in cardiac myocytes, the effects of two purported phospholipase inhibitors, mepacrine and U26,384, were evaluated. Cultured neonatal rat ventricular myocytes were pretreated for 90 minutes with 5 to 10 microM U26,384 (a steroidal diamine) or 10 to 50 microM mepacrine (an alkyl acridine) and then treated for 3 hours with 30 microM of the metabolic inhibitor, iodoacetic acid (IAA), with or without an additional dose of drug. IAA treatment resulted in a marked reduction in ATP level and a several-fold increase in free fatty acid radioactivity released from myocytes prelabeled with tritiated arachidonic acid (3H-AA). U26,384 produced substantial inhibition of the increased 3H-AA release, and was effective when given as a single pretreatment dose before IAA exposure or as continuous treatment before and during IAA exposure (for example, with 5 microM U26,384, the percentage of 3H-AA release versus IAA alone was 8% +/- 2% [SEM] [N = 15] for pretreatment only and 13% +/- 4% [N = 10] for continuous treatment). Mepacrine also resulted in significant reduction in 3H-AA release, but was more effective when given as continuous treatment (for example, with 50 microM mepacrine, the percentage of 3H-AA release versus IAA alone was 43% +/- 9% [N = 6] for pretreatment only and 22% +/- 7% [N = 9] for continuous treatment). More detailed analysis showed that U26,384 and mepacrine blocked the IAA-induced redistribution of 3H-AA into free fatty acids from other lipid species. Electron probe x-ray microanalysis of freeze-dried cryosections revealed marked electrolyte derangements in myocytes exposed to IAA, including a 24-fold increase in cellular Ca, a four fold increase in cellular Na, and a seven fold decrease in cellular K, and associated changes in cytoplasm and mitochondria. U26,384 treatment markedly reduced these electrolyte abnormalities, and maintained normal Ca levels in some protocols. Mepacrine treatment was less effective, but did produce normal Ca levels in 50% of myocytes. Prevention of IAA-induced cellular hypercontraction and blebbing also was observed. These data support the hypothesis that reduction of free fatty acid accumulation by inhibition of accelerated phospholipid degradation is associated with protection of myocytes from calcium loading and morphologic damage during inhibition of ene

Interaction of the local anesthetics dibucaine and tetracaine with sarcoplasmic reticulum membranes. Differential scanning calorimetry and fluorescence studies

The local anesthetics dibucaine and tetracaine inhibit the (Ca2+ + Mg2+)-ATPase from skeletal muscle sarcoplasmic reticulum [DeBoland, A. R., Jilka, R. L., & Martonosi, A. N. (1975) J. Biol. Chem. 250, 7501-7510; Suko, J., Winkler, F., Scharinger, B., & Hellmann, G. (1976) Biochim. Biophys. Acta 443, 571-586]. We have carried out differential scanning calorimetry and fluorescence measurements to study the interaction of these drugs with sarcoplasmic reticulum membranes and with purified (Ca2+ + Mg2+)-ATPase. The temperature range of denaturation of the (Ca2+ + Mg2+)-ATPase in the sarcoplasmic reticulum membrane, determined from our scanning calorimetry experiments, is ca. 45-55 degrees C and for the purified enzyme ca. 40-50 degrees C. Millimolar concentrations of dibucaine and tetracaine, and ethanol at concentrations higher than 1% v/v, lower a few degrees (degrees C) the denaturation temperature of the (Ca2+ + Mg2+)-ATPase. Other local anesthetics reported to have no effect on the ATPase activity, such as lidocaine and procaine, did not significantly alter the differential scanning calorimetry pattern of these membranes up to a concentration of 10 mM. The order parameter of the sarcoplasmic reticulum membranes, calculated from measurements of the polarization of the fluorescence of diphenylhexatriene, is not significantly altered at the local anesthetic concentrations that shift the denaturation temperature of the (Ca2+ + Mg2+)-ATPase.(ABSTRACT TRUNCATED AT 250 WORDS)

Topical ocular anesthetics affect epithelial cytoskeletal proteins of wounded cornea

The purpose of this study was to characterize by immunofluorescent microscopy, the cytoskeletal proteins actin and myosin and the protein calmodulin (CaM) in trephined, n-heptanol treated murine corneal epithelium during in vitro organ culture before and following topical ocular anesthetic application. The study has shown that corneal epithelial wounds exposed to anesthetic agents fail to close, even after 24 hr of culture. Failure of the wound to close was accompanied by a general decrease in immunofluorescence for actin myosin and CaM following application of the anesthetics.

Effect of chlorpromazine on the development of experimental glomerulonephritis and Arthus reaction

Chlorpromazine blocks antibody-mediated redistribution of cell surface antigens in vitro and in vivo and inhibits the development of passive Heymann glomerulonephritis, a disease characterized by in situ formation of immune complexes (Camussi et al J Immunol 1986, 136:2127-2135). The aim of this study was to establish whether chlorpromazine exerts similar effects in other rat models characterized by in situ formation of immune complexes. In glomerulonephritis induced by antibodies reactive with an exogenous antigen "planted" in glomeruli pretreatment with chlorpromazine prevented formation of "humps" and exudative and proliferative lesions. Likewise, chlorpromazine prevented passive reverse Arthus reaction in the skin. In contrast, the drug was ineffective when these lesions were already established, and also failed to inhibit the fulminant course of nephrotoxic serum glomerulonephritis with an enhanced autologous phase. It is proposed that the antiinflammatory effect of chlorpromazine is due to its ability to block the recruitment of inflammatory cells and the release of inflammatory mediators.

Effects of proparacaine on actin cytoskeleton of corneal epithelium

Chronic use of proparacaine, a topical ocular anesthetic, is associated with punctate keratopathy and delayed epithelial wound healing. Spreading corneal epithelial cells normally elaborate cytoplasmic arrays of actin-rich stress fibers which insert onto the inner surface of the cell membrane at discrete adhesion complexes. As actin is implicated in cell-to-substratum adhesion and cell motility, the effects of proparacaine on the actin cytoskeleton of corneal epithelial cells were studied in vitro. Spreading rat corneal epithelial cells in tissue culture were treated with proparacaine hydrochloride. At the lowest drug concentration used (0.01 mM), no effects were seen on the actin cytoskeleton. At 1.0 mM, some disruption of stress fibers was evident and actin was redistributed in a diffuse fashion. Many of the intact stress fibers had abnormal morphology, distribution, and orientation. Scanning electron microscopy showed a loss of cell extensions and cell-to-substratum adhesiveness at the leading epithelial edge. Above 1.0 mM, cell spreading was completely abolished and most cells detached from the substratum. After a washout period with drug-free media, these effects were reversible at concentrations of 1.0 mM or less. We postulate that one mechanism by which proparacaine inhibits corneal epithelial migration and adhesion is through alteration of the actin cytoskeleton.

Central nervous system stimulants: neuropharmacological mechanisms

The mechanisms underlying CNS-stimulant drug discrimination are discussed. Although different doses of CNS stimulants may produce qualitatively different cues, it appears that a relatively low dose of d-amphetamine (e.g., 1 mg/kg) elicits a "general" CNS-stimulant cue. Presynaptically, this cue may primarily depend on release of endogenous dopamine whereas inhibition of dopamine reuptake, per se, is insufficient to elicit the cue. Postsynaptically, the involvement of both dopamine D-1 and D-2 receptors is implicated. Furthermore, in the drug discrimination situation, D-1/D-2 receptors may be coupled differently than in dopamine-dependent locomotor activation. Anatomically, CNS-stimulant drug discrimination may depend primarily on mesolimbic dopamine systems.

Effects of local anaesthetics on short-term desensitization of guinea-pig taenia caecum to histamine

1 Short-term desensitization to histamine was induced by incubating guinea-pig taenia caecum with 10(-4)M histamine for 30 min (desensitizing incubation) in normal Locke-Ringer solution or Ca-free Locke-Ringer solution containing 0.2 mM EGTA. This desensitization was measured as a reduction of the maximal contractile response. 2 The effects of the presence of local anaesthetics during the desensitizing incubation were examined. Results showed that tetracaine, procaine, procainamide, oxybuprocaine and lignocaine inhibited the desensitization, whereas dibucaine, benzocaine and mepivacaine did not. 3 The inhibitory effects of these drugs on the desensitization were not correlated with their lipid solubility nor with the potency of their known effects, such as membrane stabilization, Ca channel blockade, calmodulin antagonism, or inhibition of C-kinase. 4 It is concluded that the inhibitory effects of local anaesthetics on the desensitization are not due to their non-specific membrane-stabilizing effects per se, but to some other action.

Trifluoperazine-sensitive activation of the spontaneous transmitter release at the frog motor endplates by low doses of procaine

Low concentrations of procaine (10(-6)-5 X 10(-5) mol/l) induced a significant increase of the spontaneous quantal transmitter release in the neuromuscular junctions of the frog cutaneous pectoris nerve-muscle preparation. The frequency of miniature endplate potentials (mepps) was increased although their size slightly decreased probably on the account of a partial block of Na+-channels at the postsynaptic membrane. The activatory effect of pre-caine was not altered under experimental conditions known to change the Ca2+ fluxes across the nerve terminal membrane such as using a Ca2+-free Ringer, or a Ca2+-channel blocker (D600), a high K+ Ringer or, finally, a low Na+ Ringer. In the presence of caffeine no change of procaine-induced activation appeared. Trifluoperazine (TFP), in a concentration known to specifically block calmodulin, completely blocked the procaine-induced increase of mepp frequency. These data suggest that procaine presumably by way of a calmodulin-dependent mechanism is related to the free cytosolic Ca2+ equilibrium. It is possible that procaine increases the free cytosolic Ca2+ concentration by blocking an active calmodulin-dependent Ca2+ extrusion mechanism.

Ontogenetic changes in adenylate cyclase, cyclic AMP phosphodiesterase and calmodulin in chick ventricular myocardium

The activities of cyclic AMP phosphodiesterase (3',5'-cyclic nucleotide 5'-nucleotidohydrolase, EC 3.1.4.17) and adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] and calmodulin content during development of chick ventricular myocardium were determined. The specific activity of cyclic AMP phosphodiesterase was relatively low in early embryos, increased during embryogenesis by about 4-fold to reach highest values just before hatching, and then decreased by approx. 30% within 1 week after hatching. In contrast, adenylate cyclase did not change during embryonic development, but increased by approx. 50% within 1 week after hatching. Calmodulin content remained constant at 9 micrograms/g wet wt. during embryonic development and decreased to 6 micrograms/g wet wt. by 1 week after hatching. DEAE-Sephacel chromatography of chick ventricular supernatant revealed a single major form of cyclic nucleotide phosphodiesterase activity in early embryonic (9-day E) and hatched (6-day H) chicks. This enzyme form was eluted at approx. 0.27 M-sodium acetate, hydrolysed both cyclic AMP and cyclic GMP, and was sensitive to stimulation by Ca2+-calmodulin, with an apparent Km for calmodulin of approx. 1 nM. In contrast, ventricular supernatant from late-embryonic (18-day E) chicks contained two forms of phosphodiesterase separable on DEAE-Sephacel: the same form as that seen at other ages, plus a cyclic AMP-specific form which was eluted at approx. 0.65 M-sodium acetate and was insensitive to stimulation by Ca2+-calmodulin. The ontogenetic changes in cyclic AMP phosphodiesterase activity in chick ventricular myocardium are consistent with reported ontogenetic changes in the steady-state contents of cyclic AMP in this tissue and suggest that this enzyme may be responsible for the changes that occur in this nucleotide during development of chick myocardium.

Identification and characterization of a Ca2+-calmodulin-sensitive cyclic nucleotide phosphodiesterase in a human lymphoblastoid cell line

This study examines the pattern and regulatory properties of cyclic nucleotide phosphodiesterases in a human lymphoblastoid B-cell line (RPMI 8392) established from a patient with acute lymphocytic leukaemia. In this cell line, phosphodiesterase activity measured at 0.25 microM-cyclic AMP is approx. 7-fold greater than that in isolated human peripheral-blood lymphocytes, and 16% of the phosphodiesterase activity in RPMI 8392 cells is associated with particulate fractions. Phosphodiesterase activity in crude fractions of this cell line is reproducibly stimulated by about 60-80% by Ca2+-calmodulin. In the presence of 20 nM-calmodulin, half-maximal stimulation occurs at 0.7 microM-Ca2+. The cytosolic phosphodiesterase activity of RPMI 8392 cells is separated into two forms by DEAE-Sephacel chromatography. The first form is eluted at approx. 0.2 M-sodium acetate, catalyses the hydrolysis of both cyclic AMP and cyclic GMP, and is stimulated 3-fold by Ca2+-calmodulin. This form exhibits non-linear kinetics for cyclic AMP in the absence of calmodulin, with extrapolated Km values of 0.8 and 4 microM, and non-linear kinetics in the presence of calmodulin, with extrapolated Km values of 0.5 and 1 microM. The Vmax. values are increased approx. 3-fold by calmodulin. The second form is eluted at approx. 0.6 M-sodium acetate, is specific for cyclic AMP, and insensitive to stimulation by Ca2+-calmodulin. The Ca2+-calmodulin-sensitive phosphodiesterase from the DEAE-Sephacel column can be adsorbed to a calmodulin-Sepharose affinity column and eluted with EGTA. This enzymic activity can also be immunoprecipitated by a monoclonal antibody directed against a calmodulin-bovine heart phosphodiesterase complex. This study documents the existence of Ca2+-calmodulin-sensitive phosphodiesterase in a cultured lymphoblastoid cell line derived from a leukaemic patient.

Calcium-dependent regulation of phospholipase A2 and its inhibitors, including tetracaine, for acetylcholine receptor cluster formation in mouse myotubes co-cultured with spinal cord explant

Regulatory effects of phospholipase A2 (PLA2) on acetylcholine receptor (AChR) cluster formation were investigated in developing mouse myotubes co-cultured with spinal cord explant, using quinacrine, cortisone, tetracaine and related agents. AChR was visualized using the fluorescence-conjugated alpha-bungarotoxin. Peak fluorescence intensity and total fluorescence within the fluorescence stain were measured as indices of AChR cluster formation and AChR content, respectively. Both indices were gradually increased from day 9 to 13 in culture. PLA2 (0.2-1.0 micrograms/ml), melittin (10 micrograms/ml) and arachidonic acid (100 microM), added to the culture medium from the second day, clearly inhibited both indices at days 11 and 13, whereas the addition of phospholipase C (1 microgram/ml) inhibited peak fluorescence but did not affect total fluorescence. The co-existence of PLA2 with its inhibitors--quinacrine (3 microM), cortisone (0.01 microM) and tetracaine (30 microM)--significantly overcame the PLA2-induced inhibition of both indices. The elevation of calcium ion concentrations from 2.9 to 10 mM abolished the increase of both indices. Quinacrine (10 microM), cortisone (0.1 microM) and tetracaine (100 microM) alone similarly inhibited both fluorescence indices. The addition of EGTA (2 mM) from day 8 overcame tetracaine-induced inhibition but not quinacrine- or cortisone-induced inhibition. These results suggest that the formation of AChR clusters in developing myotubes is negatively controlled by endogenous PLA2 activity. This overcoming of PLA2-induced inhibition by tetracaine may be dependent on calcium ion mobilization, whereas that by quainacrine and cortisone may not.

Inhibition of fast axonal transport in bullfrog nerves by dibenzazepine and dibenzocycloheptadiene calmodulin inhibitors

The effects of the calmodulin inhibitors amitriptyline, desipramine, imipramine, and clomipramine on fast axonal transport, oxidative metabolism, and density of axonal microtubules were measured in bullfrog spinal nerves in vitro. The four drugs tested inhibited the fast orthograde transport of [3H]leucine-labelled proteins and the fast retrograde transport of acetylcholinesterase at a concentration of 0.2 mM. Amitriptyline, desipramine, and imipramine were equipotent inhibitors of transport, and clomipramine was a more potent inhibitor than imipramine. The adenosine triphosphate content of the nerves was reduced by at most 19% by the compounds under study; such a reduction cannot account for the inhibition of fast axonal transport. Desipramine and imipramine had no significant effect on the density of microtubules in unmyelinated axons, whereas amitriptyline only reduced it by 18%; the inhibition of axonal transport by these three drugs can therefore not be explained by microtubule disruption. Clomipramine reduced microtubular density by 40%, and this effect may have contributed to the inhibition of fast axonal transport. The inhibition of fast axonal transport by desipramine, imipramine, and amitriptyline may be related to the inhibition of calmodulin function by these drugs. The similar potency of these three drugs as inhibitors of fast axonal transport goes in parallel with their known similar potency as calmodulin antagonists.

Local anesthetics inhibit the Ca2+, Mg2+-ATPase activity of rat brain synaptosomes

Many biochemical effects of local anesthetics are expressed in Ca2+-dependent processes [Volpi M., Sha'afi R.I., Epstein P.M., Andrenyak P.M., and Feinstein M.B. (1981) Proc. Natl. Acad. Sci. USA 78, 795-799]. In this communication we report that local anesthetics (dibucaine, tetracaine, lidocaine, and procaine and the analogue quinacrine) inhibit the Ca2+-dependent and the Mg2+-dependent ATPase activity of rat brain synaptosomes and of membrane vesicles derived from them by osmotic shock. This inhibition is induced by concentrations of these drugs close to their pharmacological doses, and a good correlation between K0.5 of inhibition and their relative anesthetic potency is found. The Ca2+-dependent ATPase is more selectively inhibited at lower drug concentrations. The physiological relevance of these findings is discussed briefly.

Electrophysiological effects of tetracaine in single guinea-pig ventricular myocytes

The effect of tetracaine on the ionic current in enzymatically dissociated single guinea-pig ventricular cells was studied using a two micro-electrode voltage-clamp technique. The myocytes were pre-incubated with Cs+ and the experiments were performed at room temperature in order to reduce the contribution of the delayed outward current. Tetracaine decreased the maximum rate of rise of the action potential with a dissociation constant (KD) strongly dependent on the holding potential (0.77 microM at -80 mV, and 6.2 microM at -95 mV). Application of 20 microM-tetracaine resulted in about a 50% reduction of the inwardly rectifying K+ current, while ten times higher concentrations were required to suppress the delayed K+ current. The inactivation time course of the Ca2+ current could be fitted with two exponentials, with time constants tau f = 15 ms and tau s = 150 ms at around 0 mV. Tetracaine decreased the amplitude of the Ca2+ current and speeded its decay. This effect was found to be primarily due to a marked inhibition of the amplitude of the slowly inactivating component (apparent KD = 80 microM, nH = 2). The drug had little effect on the time constants of the two components of Ca2+ channel inactivation. When Sr2+ or Ba2+ were the charge carriers, inactivation of the Ca2+ channel was again fitted with a fast and a slow exponential. In addition, a maintained (or very slowly inactivating) component was present. Tetracaine not only suppressed the amplitudes of the slowly inactivating and the maintained components, but also decreased the time constant of the slowly inactivating component. The results are consistent with a direct effect of tetracaine on the high threshold Ca2+ channel and do not support indirect effects of the drug secondary to suppression of Ca2+ release from internal stores.