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At least 307 records · Page 17Linked to original sources

PubMed2001

High-performance liquid chromatographic assay to determine the plasma levels of HIV-protease inhibitors (amprenavir, indinavir, nelfinavir, ritonavir and saquinavir) and the non-nucleoside reverse transcriptase inhibitor (nevirapine) after liquid-liquid extraction.

A single HPLC assay was developed for therapeutic drug monitoring of 5 HIV protease inhibitors (indinavir, amprenavir, saquinavir, ritonavir, nelfinavir) and a non-nucleoside reverse transcriptase inhibitor (nevirapine) in human plasma. After liquid-liquid extraction in a mixture ethyl acetate-hexane, compounds are separated on a C18 column with a gradient elution of solvent A [acetonitrile and 0.025 M tetramethylammonium perchlorate in 0.2% aqueous trifluoroacetic acid (55:45 (v/v))] and solvent B [methanol and 0.025 M tetramethylammonium perchlorate in 0.2% aqueous trifluoroacetic acid (55:45 (v/v))]. The compounds are detected at various wavelengths: 320 nm (nevirapine), 259 nm (indinavir), 254 nm (amprenavir, nelfinavir, saquinavir) and 239 nm (ritonavir). The intra-day and inter-day precision and accuracy are lower than 15%. The limits of quantitation are 0.05 mg/l (amprenavir), 0.2 mg/l (indinavir, saquinavir, nelfinavir) and 0.4 mg/l (ritonavir, nevirapine). This method which allows to estimate simultaneously plasma levels of protease inhibitors and nevirapine can be used for therapeutic drug monitoring.

Calibration↗

PubMed2006

Beta-arrestin2-mediated internalization of mammalian odorant receptors.

Odorant receptors comprise the biggest subfamily of G-protein-coupled receptors. Although the endocytic mechanisms of other G-protein-coupled receptors have been characterized extensively, almost nothing is known about the intracellular trafficking of odorant receptors. The present study describes the endocytic pathway of mammalian odorant receptors, which bind beta-arrestin2 with high affinity and are internalized via a clathrin-dependent mechanism. After prolonged odorant exposure, receptors are not targeted to lysosomal degradation but accumulate in recycling endosomes. Odorant-induced odorant receptor desensitization is promoted by cAMP-dependent protein kinase A phosphorylation and is dependent on serine and threonine residues within the third intracellular loop of the receptor. Moreover, beta-arrestin2 is redistributed into the dendritic knobs of mouse olfactory receptor neurons after treatment with a complex odorant mixture. Prolonged odorant exposure resulted in accumulation of beta-arrestin2 in intracellular vesicles. Adaptation of olfactory receptor neurons to odorants can be abolished by the inhibition of clathrin-mediated endocytosis, showing the physiological relevance of the here described mechanism of odorant receptor desensitization. A better understanding of odorant receptor trafficking and additional insight into the molecular determinants underlying the interactions of odorant receptors with beta-arrestin2 and other trafficking proteins will therefore be important to fully understand the mechanisms of adaptation and sensitization in the olfactory epithelium.

Amino Acid Motifs↗

PubMed2005

A factor analysis for complex systems containing nimesulide.

Binary systems containing Nimesulide and PEG 4000 were prepared by the melting method in the concentration range 3-25% w/w of the drug. The systems are homogeneous in the molten state, while, after cooling, two phases were formed of different density. They were manually separated and separately studied. Upper phases are richer in PEG 4000, while the lower ones contain the drug at levels even higher than those of the starting mixtures. The two phases were examined by DSC and UV techniques; high dissolution rates were observed with upper phases, while lower phases did not display improvement with respect to a physical mixture or micronized drug. With the aim to avoid phase separation, a third component was added to the binary system containing 5% w/w drug, during the melting. The ternary systems were prepared containing sodium dodecyl sulfate, triethanolamine, polysorbate 80, poloxamer, and cetomacrogol: a homogeneous phase was obtained only in two cases (with the addition of sodium dodecyl sulfate and triethanolamine), but only in the presence of triethanolamine dissolution rate was improved. Finally, a factor analysis was performed for complex systems containing a combination of the four additives, each one at two concentrations (1.25 and 2.5% w/w), to evaluate the optimum system in terms of both kinetic and composition parameters. Results suggest that additives affect mainly the physical aspect of the formulation rather than the kinetic behavior, which appears little improved only in a few cases.

Drug Synergism↗

PubMed1998

Species-dependent enantioselective pharmacokinetics of PNU-103017, a pyrone HIV protease inhibitor.

PNU-103017, 4-Cyano-N-(3-(cyclopropyl(5,6,7,8,9,10-hexahydro-4-hydroxy- 2-oxo-2H-cycloocta(b) pyran-3-yl)methyl)phenyl)-benzenesulfonamide, is a selective HIV aspartyl protease inhibitor under evaluation as a potential oral treatment of Acquired Immunodeficiency Diseases. PNU-103017 is a racemic mixture of two enantiomers, designated PNU-103264 (R-) and PNU-103265 (S-). Stereoselective pharmacokinetics of the two enantiomers of PNU-103017 were observed in the dog, rat, and human after single and multiple dose administration of the racemate and were apparently species-dependent. Mean enantiomeric ratios of plasma concentrations (R-/S-) at each time point were greater than 1 in the dog, ranging from 1.22 to 3.06, but less than 1 in the rat and in the human, ranging from 0.44 to 0.80 and 0.23 to 0.73, respectively. A trend towards increased or decreased (farther from 1:1, R-/S-) enantiomeric ratio of plasma concentrations with time after each administration was also observed. The enantiomeric ratio remained unchanged after multiple dose administration in the rat, dog, and human although enzyme induction and increased plasma clearance were observed for both enantiomers.

Animals↗

PubMedDate not supplied

High performance liquid chromatography with chemiluminescence detection of methamphetamine and its related compounds using 4-(N,N-dimethylaminosulphonyl)-7-fluoro-2,1,3-benzoxadiazole.

A high performance liquid chromatographic assay of methamphetamine (MP) and its related compounds, i.e. ephedrine (EP), norephedrine (NE), p-hydroxymethamphetamine (p-HMP), p-hydroxyamphetamine (p-HAP) and amphetamine (AP), with peroxyoxalate chemiluminescence detection has been developed. 4-(N,N-Dimethylaminosulphonyl)-7-fluoro-2,1,3-benzoxadiazole (DBD-F) was used as a fluorescent labeling reagent. A mixture of hydrogen peroxide and bis[4-nitro-2-(3,6,9-trioxadecyloxycarbonyl)phenyl] oxalate in acetonitrile was used as a postcolumn chemiluminogenic reagent. DBD derivatives of MP and its related compounds were separated by a gradient elution with acetonitrile and 0.01 M imidazole buffer (pH 7.0) within 65 min. The detection limits (S/N = 3) for the proposed method for MP, AP, EP, NE, p-HMP and p-HAP were 27, 100, 40, 133, 25 and 133 fmol on column, respectively. The recoveries of these compounds with normal urine samples were 87.4-106.4%. The method was successfully applied to the assay of MP and its metabolites in urine samples from MP addicts. A good linear correlation for the resulted amounts of MP or AP between the proposed method and gas chromatography was obtained (r = 0.993 for MP or 0.991 for AP).

Amphetamines↗

PubMed2004

Biotransformation of N-ethyl perfluorooctanesulfonamide by rainbow trout (Onchorhynchus mykiss) liver microsomes.

Rainbow trout (Onchorhynchus mykiss) liver microsomes were incubated with N-ethyl perfluorooctanesulfonamide [N-EtPFOSA, C8F17SO2NH(C2H5)], to examine the possibility of in vitro biotransformation to perfluorooctane sulfonate (PFOS, C8F17SO3-) and perfluorooctanoate (PFOA, C7F15COO-). Incubations were performed by exposing trout liver microsomes to N-EtPFOSA at 8 degrees C in the dark. Reaction mixtures were analyzed after incubation periods of 0, 2, 4, 8, 16, and 30 h for N-EtPFOSA, PFOS, PFOA, and perfluorooctanesulfonamide (PFOSA, C8F17SO2NH2), a suspected intermediate. Amounts of PFOS and PFOSA were found to increase with incubation time, but only background levels of PFOA were detected. Three possible reaction pathways are proposed for the conversion of N-EtPFOSA to PFOS: (i) direct conversion of N-EtPFOSA to PFOS by deethylamination accompanied by conversion of the sulfone group to sulfonate, (ii) deethylation of N-EtPFOSA to PFOSA, followed by deamination to form PFOS, and (iii) direct hydrolysis of N-EtPFOSA. These findings represent the first report indicating a possible biotransformation of a perfluorosulfonamide to PFOS in fish and may help to explain the detection of PFOS, which is relatively involatile, and thus not likely to undergo atmospheric transport, in biota from remote regions.

Animals↗

PubMed1970

Carbonic acid from decarboxylation by "malic" enzyme in lactic acid bacteria.

Carbonic anhydrase studies were used to determine the primary form of carbonic acid produced from decarboxylation of l-malic acid by "malic" enzyme in malolactic strains of five different species of lactic acid bacteria. Addition of carbonic anhydrase to the reaction mixture containing crude bacterial extract and l-malic acid, at pH 7, in all five cases resulted in an increase (13 to 23%) in the rate of carbon dioxide evolution over the control. The results indicated that the primary form of carbonic acid released from "malic" enzyme was not anhydrous carbon dioxide as previously supposed and as has been shown for other decarboxylating enzymes. The standard free-energy changes of the malo-lactic reaction with the various forms of carbonic acid as the primary decarboxylation product were calculated. The reaction is less exergonic when carbonic acid, bicarbonate ion, or carbonate ion is the primary decarboxylation product compared to anhydrous carbon dioxide. The free-energy of the reaction is not biologically available to the bacteria; with carbon dioxide not the primary decarboxylation product, the potential energy lost in a malo-lactic fermentation is not as great as previously considered. Endogenous carbonic anhydrase activity was not found.

Carbon Dioxide↗

PubMed2001

Necessity of thromboxane A2 for initiation of platelet-mediated contact sensitivity: dual activation of platelets and vascular endothelial cells.

To investigate the crucial role of platelet-derived thromboxane A(2) (TXA(2)) in initiating Ag-specific contact sensitivity (CS), a platelet-dependent CS model using genetically mast cell-deficient W/W(v) mice, was provided. In vivo treatment with BAYu3405, a TXA(2) receptor antagonist, markedly suppressed CS responses in a dose-dependent manner. This inhibitory effect occurred when BAYu3405 was administered before an early initiating phase, suggesting that TXA(2) may be a potent initiator of platelet-mediated CS responses. When platelets were pretreated with BAYu3405 in vitro, platelet aggregation as well as serotonin release, which is able to induce the early phase response allowing local recruitment of CS effector T cells due to direct activation of vascular endothelial cells, was inhibited. The addition of U46619, a TXA(2) agonist, or a mixture of platelets and thrombin-enhanced expression of both ICAM-1 and VCAM-1 on isolated mouse aortic endothelial cells, which was completely abolished by pretreatment with BAYu3405. Furthermore, intradermal injection of U46619 into the ear of platelet-depleted mice led to CS responses with marked expression of ICAM-1 and VCAM-1 on the vascular endothelium. These findings suggest that TXA(2) generated from platelets activated with Ag may mediate initiation of CS responses through inducing serotonin release from platelets and the subsequent aggregation and up-regulated expression of ICAM-1 and VCAM-1 on vascular endothelial cells.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1993

Studies on carbonic anhydrase (CA) of light microsomal membranes isolated from bovine and pig gastric mucosa.

1. The occurrence and characteristics of carbonic anhydrase (CA) activity were studied in light microsomal membranes (LMM) purified from bovine gastric mucosa. 2. Bovine gastric LMM contained a high activity of CA ranging from 170 to 400 mumol.H+/min/mg protein when assayed at 0 degree C by pH-stat technique. 3. The addition of 2mM EDTA to the assay mixture increased the enzyme activity. Lower concentrations (0.5-1 mM) had no effect. 4. The enzyme activity was dose-dependently inhibited by acetazolamide and furosemide (I50: 5 x 10(-10) M and 4.8 x 10(-7) M, respectively) and by chloride ion (Ki 85 mM) and appeared to be quite stable to treatment with alkaline Triton X-100. 5. Most of the CA activity is loosely associated with the LMM since it was removed by different washing treatments. Nevertheless, after extensive washes, gastric LMM still contained CA activity suggesting the existence of a firmly membrane-associated form of CA. 6. Values of CA activity higher than those reported previously were found in pig gastric LMM. Furthermore, the washing treatments described in this work were more effective in washing CA activity off pig gastric LMM than procedures described previously.

Acetazolamide↗

PubMed1996

In vitro metabolism of a potent HIV-protease inhibitor (141W94) using rat, monkey and human liver S9.

Compound 141W94 (Vertex VX478) (3S)-tetrahydro-3-furyl N-[((S,2R)-3-(4-amino-N-isobutylbenzenesulfonamido)-1-benzyl- 2-hydroxypropyl] carbamate, is a potent HIV-protease inhibitor and is currently undergoing clinical trials. The purpose of this study was the rapid identification of the phase I and II in vitro metabolite of 141W94 using mass spectrometry. Four different sources of liver S9 fractions were used for studying comparative in vitro metabolism of 141W94. They were obtained from Arochlor-induced rat, normal (untreated) rat, cynomolgus monkey and human livers. Selected incubations were supplemented with uridine diphosphate glucuronic acid and the reduced form of glutathione. The predominant species seen in the incubation mixture was the parent compound 141W94. Metabolites arising from ring opening to form the diol and carboxylic acid and oxidation of the tetrahydrofurran ring (formation of dihydrofuran) were identified. In addition, of the two monohydroxylated products identified, one resulted from hydroxylation on the aniline ring and the other from hydroxylation at the benzylic position. Two different glucuronides were also observed. Comparing the three species, very little metabolism was seen in the normal (non-induced) rat. The metabolic profile and extent of metabolism with induced rat, monkey and human S9 was similar. Induced rat S9 incubation showed the formation of two unique metabolites that were not seen in non-induced rat, monkey and human S9 fractions. They were the monohydroxylated glucuronide and a carbamate cleavage product. The metabolites were identified using mass spectrometry based on their molecular masses and fragmentation patterns.

Animals↗

PubMed2005

SH2 domain-mediated activation of an SRC family kinase is not required to initiate Ca2+ release at fertilization in mouse eggs.

SRC family kinases (SFKs) function in initiating Ca2+ release at fertilization in several species in the vertebrate evolutionary line, but whether they play a similar role in mammalian fertilization has been uncertain. We investigated this question by first determining which SFK proteins are expressed in mouse eggs, and then measuring Ca2+ release at fertilization in the presence of dominant negative inhibitors. FYN and YES proteins were found in mouse eggs, but other SFKs were not detected; based on this, we injected mouse eggs with a mixture of FYN and YES Src homology 2 (SH2) domains. These SH2 domains were effective inhibitors of Ca2+ release at fertilization in starfish eggs, but did not inhibit Ca2+ release at fertilization in mouse eggs. Thus the mechanism by which sperm initiate Ca2+ release in mouse eggs does not depend on SH2 domain-mediated activation of an SFK. We also tested the small molecule SFK inhibitor SU6656, and found that it became compartmentalized in the egg cytoplasm, thus suggesting caution in the use of this inhibitor. Our findings indicate that although the initiation of Ca2+ release at fertilization of mammalian eggs occurs by a pathway that has many similarities to that in evolutionarily earlier animal groups, the requirement for SH2 domain-mediated activation of an SFK is not conserved.

Animals↗

PubMed1999

Population pharmacokinetics of 2% topical dorzolamide in the aqueous humor of humans.

PURPOSE: To evaluate the concentration and kinetics of dorzolamide in the aqueous humor after its topical application. METHODS: Samples of aqueous humor were collected at the beginning of routine cataract surgery at defined intervals after topical application of a 2% solution of dorzolamide. After deep-frozen storage of the samples, drug extraction was achieved with a mixture of solvents. Quantification was carried out by high-performance liquid chromatography on a reversed-phase column. RESULTS: Peak concentrations of dorzolamide in aqueous humor were reached approximately 2 hours after application with 1000 ng/ml. Average values were approximately 1000 to 700 ng/ml after 4 to 6 hours and approximately 200 ng/ml after 12 hours. Mean half-life of absorption was 1.2 hours and for elimination 3.0 hours. CONCLUSIONS: Pharmacokinetics of dorzolamide in the aqueous humor of humans are in comparable dimensions as previously reported in experimental trials in pigmented rabbits. There is a clear linear absorption and elimination kinetic, which is demonstrated using the Bateman function. A better knowledge of the distribution and kinetics of dorzolamide will help to explain its reported effects on intraocular hemodynamics, distinct from its intraocular pressure lowering effect.

Absorption↗

PubMed2002

Discovery of further pyrrolidine trans-lactams as inhibitors of human neutrophil elastase (HNE) with potential as development candidates and the crystal structure of HNE complexed with an inhibitor (GW475151).

Described herein is a modern approach to the rapid preparation and evaluation of compounds as potential back-up drug candidates. GW311616A, 1, a derivative of pyrrolidine trans-lactams, has previously been described as a potent, orally active inhibitor of human neutrophil elastase (HNE) for the treatment of respiratory disease. These properties made it a suitable candidate for development. Described here is the discovery of three further derivatives of pyrrolidine trans-lactams, which fulfill the criteria required for back-up candidates 28, 29, and 32. These include increased activity in inhibiting HNE in human whole blood (HWB) and comparable pharmacokinetic properties, in particular clearance, in two species. To provide a rapid assessment of clearance, cassette dosing in dog was used. Modern array techniques, including the synthesis of mixtures, were used to synthesize compounds rapidly. Having selected three potential compounds as back-up candidates, they were prepared as single enantiomers and profiled in in vitro and in vivo assays and evaluated pharmacokinetically in rat and dog. These compounds are highly potent and selective HNE inhibitors, with a prolonged pharmacodynamic action. Pharmacokinetically, these compounds are comparable with 1 while they are more potent in HWB. Compound 28, however, has a higher clearance. One of these compounds, 32, was cocrystallized with HNE, and features of this structure are described and compared with the cocrystal structure of 1 in porcine pancreatic elastase.

Animals↗

PubMed1990

A Ca2(+)-activated, Mg2(+)-dependent ATPase with high affinities for both Ca2+ and Mg2+ in vascular smooth muscle microsomes: comparison with plasma membrane Ca2(+)-pump ATPase.

A Ca2(+)-ATPase with a high affinity for free Ca2+ (apparent Km of 0.13 microM) was found and characterized in membrane fractions from porcine aortic and coronary artery smooth muscles in comparison with the plasma membrane Ca2(+)-pump ATPase purified from porcine aorta by calmodulin affinity chromatography. The activity of the high-affinity Ca2(+)-ATPase became enriched in a plasma membrane-enriched fraction, suggesting its localization in the plasma membrane. The enzyme was fully active in the absence of exogenously added Mg2+, but required a minute amount of Mg2+ for its activity as evidenced by the findings that it was fully active in the presence of 0.1 microM free Mg2+ but lost the activity in a reaction mixture containing trans-cyclohexane-1,2-diamine-N,N,N',N'-tetraacetic acid as a divalent cation chelator which has, unlike EGTA, high affinities for both Ca2+ and Mg2+. It was able to utilize a variety of nucleoside di- and triphosphates as substrates, such as ADP, GDP, ATP, GTP, CTP, and UTP, showing a broad substrate specificity. The activity of the enzyme was not modified by calmodulin (5, 10 micrograms/ml). Trifluoperazine, a calmodulin antagonist, had a partial inhibitory effect on the activity at 30 to 240 microM, but this inhibition could not be reproduced by a more specific calmodulin antagonist, W-7, indicating that this inhibition by trifluoperazine was not specific. Furthermore, the high-affinity Ca2(+)-ATPase activity was not modified either by low concentrations (0.5-9 microM) of vanadate or by 1-100 microM p-chloromercuribenzoic acid. Cyclic GMP, nitroglycerin, and nicorandil did not have any effect on the enzyme activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2004

Role of cyclooxygenase-2 in cytokine-induced beta-cell dysfunction and damage by isolated rat and human islets.

Type I diabetes mellitus is an autoimmune disease characterized by the selective destruction of the insulin-secreting beta-cell found in pancreatic islets of Langerhans. Cytokines such as interleukin-1 (IL-1), interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) mediate beta-cell dysfunction and islet degeneration, in part, through the induction of the inducible isoform of nitric-oxide synthase and the production of nitric oxide by beta-cells. Cytokines also stimulate the expression of the inducible isoform of cyclooxygenase, COX-2, and the production of prostaglandin E(2) (PGE(2)) by rat and human islets; however, the role of increased COX-2 expression and PGE(2) production in mediating cytokine-induced inhibition of islet metabolic function and viability has been incompletely characterized. In this study, we have shown that treatment of rat islets with IL-1beta or human islets with a cytokine mixture containing IL-1beta + IFN-gamma +/- TNF-alpha stimulates COX-2 expression and PGE(2) formation in a time-dependent manner. Co-incubation of rat and human islets with selective COX-2 inhibitors SC-58236 and Celecoxib, respectively, attenuated cytokine-induced PGE(2) formation. However, these inhibitors failed to prevent cytokine-mediated inhibition of insulin secretion or islet degeneration. These findings indicate that selective inhibition of COX-2 activity does not protect rat and human islets from cytokine-induced beta-cell dysfunction and islet degeneration and, furthermore, that islet production of PGE(2) does not mediate these inhibitory and destructive effects.

Animals↗

PubMed1997

Low level determination of dorzolamide and its de-ethylated metabolite in human plasma by liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry.

A sensitive and specific method for the determination of dorzolamide (I) and its de-ethylated metabolite (II) in human plasma has been developed utilizing high pressure liquid chromatography (HPLC) with tandem mass spectrometric (MS/MS) detection. The analytes and internal standard (III) were isolated from the deproteinized pH 8.0 buffered plasma, using a liquid-liquid extraction with a mixture of ethyl acetate, toluene, and isopropanol. The analytes were then back extracted into 0.085% phosphoric acid (200 microliters) and after washing the acidic extract with hexane, the organic layer was discarded and a fraction (50 microliters) of the acid extract was injected into the LC/MS/MS system. The MS/MS detection was performed on a PE Sciex API III tandem mass spectrometer using a heated nebulizer interface. Multiple reaction monitoring of the parent-->product ion combinations of m/z 325-->199, 297-->199, and 397-->306 were used to quantify I, II, and III, respectively. The assay was validated in the concentration ranges of 0.5-100 and 2.5-100 ng ml-1 of plasma for I and II, respectively. The precision of the assays, expressed as coefficients of variation (C.V.%), were less than 10% over the entire concentration range, with adequate assay specificity and accuracy. The LC/MS/MS method provided a 10-fold increase in the sensitivity of I over the previously reported HPLC/UV method [1].

Antihypertensive Agents↗

PubMed1998

Hypoxic pulmonary vasoconstriction in pigs: role of endothelin-1, prostanoids and ATP-dependent potassium channels.

This study investigated the mechanisms that may contribute to the hypoxic pulmonary vasoconstriction and compared the effects of hypoxia on pulmonary and systemic vascular beds. Six anesthetized spontaneously breathing pigs inhaled a hypoxic mixture (10% O2 in air) in control conditions and after pre-treatment with Indomethacin (3 mg kg(-1) i.v.) to block the cyclooxygenase pathway. During hypoxia, the Indomethacin pre-treated pigs were given Cromakalim (80 microg kg(-1) i.v.) to activate K+(ATP) channels. Bosentan (5 mg kg(-1) i.v.) was administered to block endothelin-1 receptors and then during hypoxia Cromakalim was administered as before. In all experimental conditions we recorded breathing pattern and vascular parameters: mean systemic and pulmonary arterial pressures; systemic and pulmonary vascular resistances; cardiac output; and heart rate. Vascular and respiratory responses to hypoxia were determined when PaO2 was reduced to 50 +/- 5 mmHg. The main finding was that in spontaneously breathing pigs, hypoxia induces pulmonary vasoconstriction and an increase in mean systemic arterial pressure, which are cyclooxygenase-independent. A role of endothelin-1 appears in both vascular districts, but pulmonary vasoconstriction may also be due to ET-1-dependent inhibition of K+(ATP) channels.

Adenosine Triphosphate↗

PubMed2001

Direct autocrine inhibition and cAMP-dependent potentiation of single L-type Ca2+ channels in bovine chromaffin cells.

Using the cell-attached recording configuration, we found that in adult bovine chromaffin cells there exists a direct membrane-delimited inhibition of single Bay K-modified L-channels mediated by opioids and ATP locally released in the recording pipette. This autocrine modulation is mediated by pertussis toxin (PTX)-sensitive G-proteins and causes a 50 % decrease of the open channel probability (Po) and an equivalent percentage increase of null sweeps at +10 mV with no changes to the activation kinetics, single channel conductance and mean open time. The decrease in Po is mainly due to an increase in the occurrence and duration of slow closed times (> 40 ms). Addition of purinergic and opioidergic antagonists (suramin and naloxone) or cell pre-treatment with PTX removes the inhibition while addition of ATP and opioids inside the pipette, but not outside, mimics the effect. Strong pre-pulses (+150 mV, 280 ms) followed by short repolarizations are unable to remove the inhibition at test potential (+10 mV). Increasing the level of cAMP by either direct application of 8-(4-chlorophenylthio)-cAMP (8-CPT-cAMP) or mixtures of forskolin and 1-methyl-3-isobutylxanthine (IBMX) potentiates the activity of L-channels by increasing the mean open time and decreasing the mean closed time and percentage of null sweeps. The cAMP-induced potentiation occurs regardless of whether the G-protein-mediated inhibition is activated by ATP and opioids or inactivated by PTX. Protein kinase inhibitors (H7 and H89) prevent the effects of cAMP without altering the basal autocrine modulation associated with PTX-sensitive G-proteins. Our results provide new evidence for the coexistence of two distinct modulations that may converge on the same neuroendocrine L-channel: a direct G-protein-dependent inhibition and a cAMP-mediated potentiation, which may work in combination to regulate Ca2+ entry during neurosecretion.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗