Increased expression of opioid delta receptors by deoxy conformation heme proteins in NG108-15 cells

Adaptations to prolonged hypoxia include an increase in the expression of proteins that may facilitate survival. One mechanism by which hypoxia increases protein expression involves a change of heme proteins from oxygenated to deoxygenated conformations. In the present study, we tested the hypothesis that treatment of NG108-15 cells with metallic cations, which are known to induce a deoxygenated conformation of heme proteins, would increase delta opioid receptor (DOR) expression. Cells were treated with cobalt and nickel, which induce deoxygenated heme protein conformation, or zinc as a control for 48 h prior to quantifying DOR expression. Cobalt and nickel, but not zinc, significantly increased DOR expression. Heme synthesis inhibitors would block the synthesis of cobalt-substituted heme proteins which are locked in a deoxygenated conformation. The cobalt-induced increase in DOR expression was blocked by the heme synthesis inhibitor, 4,6-dioxoheptanoic acid. These experiments indicate that deoxygenated conformation heme proteins, which are thought to partially mimic hypoxia, increase DOR expression. The increase in DOR expression suggests that the DOR gene may be hypoxia-sensitive. Further, the increase in DOR expression suggests a potential adaptation strategy to hypoxia and may represent one of the first findings of physiological regulation of DOR expression.

Regulation of airway muscarinic cholinergic receptor subtypes by chronic anticholinergic treatment

Anticholinergic agents are commonly used as bronchodilators for patients with airway obstructive diseases. The effects of chronic anticholinergic therapy on airway function and bronchial responsiveness are not known, but data from clinical studies suggest the possibility of adverse effects. We demonstrated in rabbits that, after atropine treatment for 4 weeks, the efficacy (maximum contraction) of in vitro methacholine-induced contraction of mainstem bronchi was increased [control (untreated), 1.0 +/- 0.1 g; atropine-treated, 1.6 g +/- 0.2 g; p = 0.04]. However, there was no significant change in the potency (EC50) of methacholine-induced contraction. Chronic atropine treatment increased the maximum density (Bmax) of muscarinic receptors in the airways, as determined by radioligand binding studies with tritiated quinuclidinyl benzilate. Individual muscarinic receptor subtypes were measured using antibodies selective for the m1-m5 subtypes. Of the subtypes detected in rabbit tracheal smooth muscle (m2, m3, and m4), only the m2 and m3 muscarinic receptor subtypes were significantly up-regulated compared with control, after chronic atropine treatment. Because cholinergic agent-mediated contraction of smooth muscle has been shown to be mediated by m3 muscarinic receptors, the atropine-induced increase in the methacholine response in airway smooth muscle appears to be the result of the up-regulation of m3 muscarinic cholinergic receptors. Such a mechanism may explain the clinical observations that chronic anticholinergic therapy for asthmatic patients is associated with an increase in bronchial responsiveness and that continuous versus "on demand" anticholinergic bronchodilator therapy may cause an accelerated decline in ventilatory function.

Treatment with antisense oligodeoxynucleotide to a conserved sequence of opioid receptors inhibits antinociceptive effects of delta subtype selective ligands

Previous work has suggested the existence of subtypes of the delta opioid receptor (DOR) which have been termed delta1 and delta2. [D-Ala2, Glu4]deltorphin has been suggested to selectively elicit antinociception via the delta2 receptor while [D-Pen2, D-Pen5]enkephalin (DPDPE) is thought to act via the delta1 receptor. Treatment with an antisense oligodeoxynucleotide (oligo) directed towards the N-terminal portion of the cloned DOR has been demonstrated to selectively inhibit the antinociceptive actions of [D-Ala2, Glu4]deltorphin, but not of DPDPE, suggesting that the cloned DOR corresponds to that pharmacologically defined as delta2. Here, an antisense oligo (or a mismatch sequence) was designed to target a conserved region of the cloned mu, delta and kappa opioid receptor. These oligos were employed in order to determine whether the antinociceptive effects of [D-Ala2, Glu4]deltorphin, as well as DPDPE, could be inhibited. The data indicate that the antinociceptive actions of both ligands were inhibited by treatment with this antisense, but not with the mismatch oligo. Taken together, the results of the treatments with oligos directed towards the N-terminal portion of the cloned DOR and with that directed to the conserved region of the opioid receptors suggest that (a) DPDPE effects are mediated by a subtype of the DOR which shares a domain common to the cloned opioid receptors, and (b) the N-terminal region differs between these putative DOR subtypes.

Expression of cDNA fragment encoding sperm membrane peptide in E. coli

A secretory high-level expression cloning vector designated as pSBC-20 was constructed by inserting a DNA fragment encoding the signal peptide of ompA protein into pBV 220 vector. Any foreign DNA fragment can be inserted into the polylinker cloning sites located after the secretion signal sequence. The cloned foreign gene is under the control of the PR-PL promoter while the expression of the gene is regulated by the cI-gene product. The products are secreted into the periplasmic space of bacteria or into the medium. A recombinant plasmid (pRSD-220) was constructed by inserting the 210 bp from RSD-2, a cDNA encoding a peptide fragment of human sperm protein, into the EcoRI site of pSBC-20. The E. coli cells transformed with pRSD-220 were propagated at 30 degrees C, then incubated at 42 degrees C for several hrs. The cloned gene product was secreted into the culture medium at a high rate. The yield was about 60 mg of gene product per liter of cultured medium.

Opioid peptide receptor studies. 1. Identification of a novel delta-opioid receptor binding site in rat brain membranes

Our laboratory was among the first to propose the existence of delta receptor subtypes: a delta site thought to be associated with a mu-delta-opioid receptor complex termed the delta cx binding site and delta site not associated with the mu-delta-opioid receptor complex, termed the delta ncx site. In previous studies, we assayed the delta cx site with [3H][D-Ala2,D-Leu5]enkephalin using rat brain membranes depleted of delta ncx sites by pretreatment with the site-directed acylating agent, (+)-trans-SUPERFIT. In the present study, we investigated, using (+)-trans-SUPERFIT-pretreated membranes, the possibility of heterogeneity of the delta cx binding site. Two sites were resolved: the delta cx-1 site at which mu ligands are potent noncompetitive inhibitors and delta ligands are weak competitive inhibitors, and the delta cx-2 site where delta ligands are potent and mu ligands are weak, mixed competitive-noncompetitive inhibitors. Although the delta cx-2 site has a delta-like ligand-selectivity profile, several experiments distinguished it from the delta ncx site. Two lines of evidence suggest that the delta ncx site corresponds to the cloned delta receptor. One, the delta receptor was cloned from the NG108-15 cell line, and this receptor, like the delta ncx binding site, irreversibly binds SUPERFIT and (+)-trans-SUPERFIT. Secondly, administration of delta-antisense DNA selectively decreases delta ncx binding. Viewed collectively, the major finding of this study is the discovery of a novel SUPERFIT-insensitive and delta-antisense-insensitive delta cx-2 binding site.

Antisense oligodeoxynucleotide to the CCKB receptor produces naltrindole- and [Leu5]enkephalin antiserum-sensitive enhancement of morphine antinociception

Cholecystokinin (CCK) has been shown to attenuate, while CCK antagonists enhance, the antinociceptive activity of morphine, suggesting that this peptide may act as an endogenous modulator of the opioid system. Here, we have investigated the effects of administration of a synthetic oligodeoxynucleotide (oligo) complementary to the 5' coding region of the cloned mouse CCKB receptor (antisense), or a mismatch oligo, on the antinociceptive effects of morphine. Intracerebroventricular (i.c.v.) treatment of mice with CCKB antisense, but not mismatch, oligo for 3 days resulted in an enhancement of the antinociceptive potency of i.c.v. morphine, as indicated by an approximately 6-fold leftward shift of the dose-effect curve. The antinociceptive effects of morphine in control and CCKB antisense-treated animals were investigated in the presence or absence of naltrindole, an opioid delta receptor antagonist, as well as in the presence or absence of antisera directed against either [Leu5]- or [Met5]enkephalin. The enhanced potency of morphine in mice pretreated with CCKB antisense oligo was blocked by a delta-selective dose of naltrindole and antisera to [Leu5]enkephalin, but not [Met5]enkephalin; naltrindole, or antisera towards [Leu5]enkephalin or [Met5]enkephalin did not produce antinociceptive effects when given alone and did not alter the antinociceptive actions of morphine in control mice. These data suggest that CCK may act via CCKB receptors to tonically inhibit the release of [Leu5]enkephalin, or a [Leu5]enkephalin-like peptide. The enhancement of morphine antinociception seen in the presence of blockade of the CCKB receptor may be the result of the well-known enhancement of morphine antinociception by opioid delta agonists.

Doppler sonography of adnexal masses: the predictive value of the pulsatility index in benign and malignant disease

OBJECTIVE

The purpose of this study was to determine whether pulsed Doppler sonography can be used to distinguish between benign and malignant adnexal masses on the basis of pulsatility index.

SUBJECTS AND METHODS

In an 18-month period, all patients in whom an adnexal mass was detected at sonography had further evaluation of the mass by color and pulsed Doppler sonography. Ninety-nine patients with 102 masses that were surgically removed were included in the study. The pulsatility indexes were calculated from the reproducible spectral waveforms generated from flow centrally or peripherally within or immediately adjacent to the mass. Each lesion was categorized on the basis of its gray scale morphologic features as typically benign or indeterminate/malignant in appearance.

RESULTS

Of the 102 adnexal masses, 89 were benign and 13 were malignant. In seven of the 89 benign lesions, no flow could be detected, and these were excluded from analysis. Of the remaining 82 benign lesions, 65 showed pulsatility indexes consistently equal to or greater than 1.0, and 17 showed pulsatility indexes of less than 1.0. Ten of the 13 malignant lesions had pulsatility indexes consistently less than 1.0, and three primary malignant tumors had their lowest pulsatility indexes ranging between 1.1 and 1.8. Sixty-five of the 68 masses with pulsatility indexes equal to or greater than 1.0 were benign, for a positive predictive value of 96% for benign disease. Ten of the 27 masses with pulsatility indexes of less than 1.0 were malignant, for a positive predictive value of 37% for malignant disease. Forty-five masses were detected in perimenopausal and postmenopausal patients. In this group, the pulsatility index had a positive predictive value of 88% for benign disease and 47% for malignant disease. In this study, 45 of 49 masses that had a typically benign sonographic appearance had pulsatility indexes equal to or greater than 1.0. All 49 masses had benign histology. In the remaining 46 masses with an indeterminate/malignant sonographic appearance, 20 of 23 with pulsatility indexes equal to or greater than 1.0 were benign, and 10 of 23 with pulsatility indexes of less than 1.0 were malignant.

CONCLUSION

Our results show a high positive predictive value of high-impedance flow in benign adnexal disease and a predominance of low-impedance flow in malignant adnexal disease. However, the pulsatility indexes showed considerable overlap between benign and malignant lesions, indicating that Doppler sonography has severe limitations in the differentiation of benign from malignant adnexal disease on the basis of low-impedance flow (pulsatility index < 1.0).

Pharmacological characterization of the cloned kappa opioid receptor as a kappa 1b subtype

Substantial pharmacological evidence in vitro and in vivo has suggested the existence of subtypes of the kappa opioid receptor. Quantitative radioligand binding techniques resolved the presence of two high affinity binding sites for the kappa 1 ligand [3H]U69,593 in mouse brain membranes, termed kappa 1a and kappa 1b, respectively. Whereas the kappa 1a site has high affinity for fedotozine and oxymorphindole and low affinity for bremazocine and alpha-neoendorphin, site kappa 1b has high affinity for bremazocine and alpha-neoendorphin and low affinity for fedotozine and oxymorphindole. CI-977 and U69,593 bind equally well at both sites. To determine the relationship between these kappa 1 receptor subtypes and the recently cloned mouse kappa 1 receptor (KOR), we examined [3H]U69,593 binding to the KOR in stably transfected cells (KORCHN-8). Competition of [3H]U69,593 binding to the KOR by bremazocine, alpha-neoendorphin, fedotozine and oxymorphindole resolved a single class of binding sites at which these agents had binding affinities similar to that of the kappa 1b site present in mouse brain. These results suggest that the cloned KOR corresponds to the kappa 1 site in mouse brain defined as kappa 1b.

Treatment with antisense oligodeoxynucleotide to the opioid delta receptor selectively inhibits delta 2-agonist antinociception

Using approaches emphasizing differential antagonism of receptor selective agonists and cross-tolerance paradigms, evidence in vivo has suggested the existence of subtypes of opioid delta receptors, which have been termed delta 1 and delta 2. Recent work has elucidated the structure of an opioid delta receptor. The present investigation attempted to continue to test the hypothesis of subtypes of delta receptors and to correlate the cloned delta receptor with the existing pharmacological classification. Synthetic oligodeoxynucleotides (oligos) complementary to the 5' end of the cloned delta receptor coding region (antisense) or its corresponding sequence (sense) were given by intracerebroventricular (i.c.v.) administration to mice, twice-daily for 3 days and antinociceptive responses to selective agonists at putative delta 1 and delta 2 receptors were subsequently determined. Treatment with antisense, but not sense, oligo significantly inhibited the response to [D-Ala2,Glu4]deltorphin (delta 2 agonist), but not to [D-Pen2,D-Pen5]enkephalin (DPDPE, delta 1 agonist). Further, subsequent administration of DPDPE elicited a full antinociceptive response in the same antisense oligo treated mice which did not show a significant response to [D-Ala2,Glu4]deltorphin while antisense oligo treated mice which responded to DPDPE did not show antinociception when tested subsequently with [D-Ala2,Glu4]deltorphin. The data suggest that the cloned delta receptor corresponds to that pharmacologically classified as delta 2 and continue to support the concept of subtypes of opioid delta receptors.

A faster-acting and more potent form of tissue plasminogen activator

Current treatment with tissue plasminogen activator (tPA) requires an intravenous infusion (1.5-3 h) because the clearance of tPA from the circulation is rapid (t 1/2 approximately 6 min). We have developed a tPA variant, T103N,N117Q, KHRR(296-299)AAAA (TNK-tPA) that has substantially slower in vivo clearance (1.9 vs. 16.1 ml per min per kg for tPA in rabbits) and near-normal fibrin binding and plasma clot lysis activity (87% and 82% compared with wild-type tPA). TNK-tPA exhibits 80-fold higher resistance to plasminogen activator inhibitor 1 than tPA and 14-fold enhanced relative fibrin specificity. In vitro, TNK-tPA is 10-fold more effective at conserving fibrinogen in plasma compared to tPA. Arterial venous shunt models of fibrinolysis in rabbits indicate that TNK-tPA (by bolus) induces 50% lysis in one-third the time required by tPA (by infusion). TNK-tPA is 8- and 13-fold more potent in rabbits than tPA toward whole blood clots and platelet-enriched clots, respectively. TNK-tPA conserves fibrinogen and, because of its slower clearance and normal clot lysis activity, is effective as a thrombolytic agent when given as a bolus at a relatively low dose.

Selective inhibition of [D-Ala2, Glu4]deltorphin antinociception by supraspinal, but not spinal, administration of an antisense oligodeoxynucleotide to an opioid delta receptor

Evidence in vivo has suggested the existence of subtypes of the delta opioid receptor (DOR), which have been termed delta 1 and delta 2. These proposed DOR subtypes are thought to be activated by [D-Pen2, D-Pen5]enkephalin (DPDPE, delta 1) and [D-Ala2, Glu4]deltorphin (delta 2). Recent work in which an antisense oligodeoxynucleotide (oligo) to a cloned DOR was administered by the intrathecal (i.th.) route has demonstrated a reduction in the antinociceptive actions of both i.th. DPDPE and [D-Ala2, Glu4]deltorphin, but not of [D-Ala2, NMPhe4, Gly-ol]enkephalin (DAMGO, mu agonist) in mice. The present investigation has extended these observations by administering the same DOR antisense oligo sequence by the intracerebroventricular (i.c.v.) route and evaluating the antinociceptive actions of i.c.v. agonists selective for delta, mu and kappa receptors. I.th. treatment with DOR antisense oligo, but not mismatch oligo, significantly inhibited the antinociceptive actions of both i.th. DPDPE and [D-Ala2, Glu4]deltorphin but not of i.th. DAMGO or U69,593 (kappa agonist), confirming previous data. In contrast, i.c.v. DOR antisense oligo, but not mismatch oligo, selectively inhibited the antinociceptive response to i.c.v. [D-Ala2, Glu4]deltorphin without altering the antinociceptive actions of i.c.v. DPDPE, DAMGO or U69,593. The data suggest that the cloned DOR corresponds to that pharmacologically classified as delta 2 and further, suggest that this delta receptor subtype may play a major role in eliciting spinal delta-mediated antinociception.

Assessment of radiolabeled stabilized F(ab')2 fragments of monoclonal antiferritin in nude mouse model

The biodistribution of 111In-labeled stabilized fragments of monoclonal antiferritin was studied in nude mice bearing a human hepatoma tumor xenograft. Pharmacokinetics and tumor targeting of fragment Fab'-linker-Fab' fragment molecules (stabilized F(ab')2) were compared to unmodified F(ab')2 fragment molecules and immunoglobulin G (IgG). Significant differences were observed in tumor and normal organ uptake at 12, 24, 48 and 72 hr. Tumor retention of stabilized F(ab')2 fragments was approximately 2.5-fold higher than of unmodified F(ab')2 at 48 hr. Blood clearance for stabilized F(ab')2 was relatively faster than intact IgG, while unmodified F(ab')2 cleared more rapidly from the circulation. Kidney radioactivity of unmodified F(ab')2 was at least two times higher than kidney radioactivity of stabilized F(ab')2 at all time points. Stabilized F(ab')2 demonstrated 40% less liver uptake than intact IgG. In these studies with nude mice, substantial retention of stabilized F(ab')2 in tumor and significant reduction in liver and kidney uptake of these fragments indicated that they could also have a higher therapeutic ratio than IgG or unmodified F(ab')2 in human patients.

Modification of the C terminus of cecropin is essential for broad-spectrum antimicrobial activity

Cecropin A is a naturally occurring peptide with bactericidal activity against gram-negative and gram-positive bacteria. Production of large quantities of bactericidal peptides that are similar in structure and activity to cecropin A has been achieved by combining recombinant DNA techniques and techniques and chemical modification. Expression of the bactericidal peptide in Escherichia coli was accomplished through the formation of a fusion protein. The 5' end of the L-ribulokinase gene was fused to a single copy of a synthetic gene encoding cecropin A. A methionine codon was engineered between the two genes, and a methionylglycine extension was introduced at the C terminus of cecropin A. Cyanogen bromide treatment of the fusion protein yielded cecropin A with a C-terminal homoserine. The recombinant cecropin A with a homoserine at the C terminus did not kill most gram-positive bacteria tested. However, recombinant cecropin A with a chemically modified C terminus has antimicrobial activity similar to that of cecropin produced by cecropia pupae.

Simplification of high-energy collision spectra of peptides by amino-terminal derivatization

Four-sector tandem mass spectrometry proves extremely useful for providing sequence information for peptides. The complexity of ion fragmentations, however, makes data interpretation difficult and time consuming. Attachment of a fixed positive charge to the peptide amino terminus forces production of only N-terminal fragment ions to yield simplified, predictable fragmentation. Reaction of a peptide at pH 6 with iodoacetic anhydride selectively modifies the N-terminus by exploiting the pK(a) differences between the alpha-amino group and any lysine side-chain epsilon-amino groups. The iodoacetyl peptide can react with many reagents to form a fixed positive charge. We find reaction with dimethyloctylamine forms a quaternary ammonium derivative with good surface activity properties and concomitant increased sensitivity. The high-energy CAD fragment ion spectra of the N-terminally derivatized peptides show predominantly a(n) and d(n) ions. The abundant d(n) ions permit ready distinction of leucine and isoleucine. Fewer fragment ions make data interpretation simpler and lead to more intense peaks since the ion intensity is spread among fewer peaks. The method is particularly useful for peptides which do not otherwise yield sufficient fragmentation to provide either the complete sequence or the locations of modified amino acids.

Spontaneous growth hormone release in term infants: changes during the first four days of life

Healthy term infants have higher umbilical cord GH levels compared to older infants and children. In the sheep, GH concentrations rapidly fall within an hour of birth; the physiology of GH release after parturition in the human term infant is less well known. The purpose of this study was to investigate spontaneous 12-h GH release in male and female term infants of varying postnatal ages. We studied 14 infants (7 males and 7 females). Subjects were divided into those studied earlier following delivery (28.2 +/- 3.4 h of age, mean +/- SE) and into those studied at a later time (74.8 +/- 3.5 h, P < 0.0005). The age at study was defined as the age (hours) when blood sampling began. There were eight infants studied at an early age (four males and four females) and six studied at a later age (three males and three females). Subjects were comparable with respect to gestational age, birth weight, and length; all were biochemically euthyroid. One infant was large for gestational age although his head circumference was in the normal range. Blood (0.1 mL) was taken every 30 min over a 12-h period from an indwelling umbilical catheter; no stress occurred during the blood withdrawal. GH was determined by a double-antibody RIA using 0.01 mL plasma. GH pulse detection was undertaken using Cluster, a computerized pulse detection algorithm. Total insulin-like growth factor I (IGF-I) was measured following separation of the IGFs from the serum binding proteins. Spontaneous pulsatile GH release was observed in all infants studied. No differences in GH characteristics were found between male and female subgroups in the early or late study groups. In subsequent analysis, the data for the males and females are combined. The GH pulse frequency per 12 h was greater in the earlier studied group, 5.1 +/- 0.9 (mean +/- SE) vs. 2.5 +/- 0.7 in the later group (P < 0.05). The maximal pulse amplitude was 47.1 +/- 7.9 micrograms/L in the early and 27.1 +/- 4.1 in the later studied group (P < 0.06). The incremental pulse amplitude was 26.4 +/- 3.4 micrograms/L in the early and 12.8 +/- 2.7 in the later group (P = 0.01). The pulse width was greater in the later studied group (202.8 +/- 71.1 min vs. 84.1 +/- 21.6, P < 0.06).(ABSTRACT TRUNCATED AT 400 WORDS)

Sclerosing peritonitis with gross peritoneal calcification: a case report

We report the case of a patient on dialysis for 13 years, including continuous ambulatory peritoneal dialysis (CAPD) for 11 years, who developed sclerosing peritonitis with gross peritoneal calcification. The patient first presented with abdominal pain in January 1990, when peritoneal calcification was detected for the first time. Her symptoms settled spontaneously and 1 year later she presented with acute peritonitis and adynamic ileus. The peritonitis settled with antibiotics and Tenchkoff catheter removal, but the ileus persisted. She was commenced on long-term parenteral nutrition, but never recovered useful bowel function. After 8 weeks of hemodialysis and total parenteral nutrition, a further laparotomy for an acute abdomen showed what appeared to be extensive bowel infarction and peritoneal calcification. She died several days later. Of significance, peritoneal calcification was first noted on x-ray and computed tomography (CT) scan while the patient was still largely asymptomatic and before peritoneal ultrafiltration capacity was significantly impaired. Unlike other reported cases of calcifying peritonitis, sclerosing peritonitis was present and calcification was far more extensive. It was not associated with factors such as frequent infective peritonitis or acetate dialysate. Calciphylaxis was not present nor was there any abnormality of calcium-phosphate metabolism. The outcome of this case suggests that patients with recurrent or persistent bowel symptoms on long-term CAPD should have early abdominal x-ray or CT scanning to exclude sclerosing peritonitis or bowel calcification. If present, consideration should be given to transferring the patient to another therapeutic dialysis modality if possible.

Chimeric M1/M2 muscarinic receptors: correlation of ligand selectivity and functional coupling with structural modifications

Chimeric M1/M2 receptors were expressed in murine fibroblasts (B82) transfected with recombinant m1/m2 receptor genes. The binding affinities of a number of muscarinic antagonists and the agonist carbachol for these chimeric receptors were compared with the ligands' affinities for the M1 and M2 receptors expressed in the B82 cells. The tricyclic compounds, namely pirenzepine (PZ), 11-([2-[(diethylamino)methyl]-1-piperidinyl]acetyl)-5,11- dihydro-6H-pyrido-[2,3-6][1,4]benzodiazepine-6-one (AF-DX 116) and himbacine, shared a binding site between transmembrane domains VI and VII. However, the selective interaction of pirenzepine with M1 and AF-DX 116 and himbacine with M2 involved different structural regions. The high-affinity binding for 4-diphenylacetoxy-N- methylpiperidine and hexahydrosiladifenidol was confined to within loop o2 and transmembrane domains V and VI, which were clearly distinguishable from those of the tricyclic compounds. These results support the hypothesis that the ligands' stereochemical features are critical in their optimal alignment within the ligand binding pocket. The cytoplasmic i3 loop modulated the binding of carbachol such that receptors which contained the i3 domain from the M2 receptor exhibited a single high-affinity state, whereas those with the i3 domain from the M1 receptor had an additional low-affinity state for the agonist. The i3 regions are essential for the differential functional coupling of the M1 and M2 receptors to second messenger systems; however, additional upstream regions seem to be essential for a potent and efficacious activation of phospholipase C by the M1 receptor. This study provides new insight into the molecular basis of ligand selectivity.

Pharmacological characterization of a novel muscarinic partial agonist, YM796, in transfected cells expressing the m1 or m2 muscarinic receptor gene

To investigate the pharmacological effect of a novel compound YM796, we performed radioligand binding experiments and correlative biochemical experiments using the transfected murine fibroblast B82 cells which expressed the m1 and m2 muscarinic receptor genes (cloned cell lines designated as LK3-3 and M2LKB2-2, respectively). [3H](-)methyl-3-quinuclidinyl benzilate [( 3H](-)MQNB) binding in these transfected cell lines was inhibited by different optical isomers of YM796 and other muscarinic drugs, atropine, pirenzepine, AF-DX 116, as well as selected agonists. (-)YM796, (+)YM796 and (+/-)YM796 inhibited [3H](-)MQNB binding in LK3-3 cells with Ki values of 16.4 microM, 30.1 microM and 21.8 microM and in M2LKB2-2 cells with Ki values of 52.0 microM, 108 microM and 77.1 microM, respectively. From functional assays we found the two isomers, (-)YM796 and (+)YM796 had different intrinsic activities for the M1 and M2 muscarinic receptors. (-)YM796 revealed agonistic activity: stimulation of [3H]IP1 accumulation in LK3-3 cells with an EC50 value of 26.5 microM, which was less efficacious (the Emax value was 5.6 times basal) than carbachol, a full agonist (the Emax value was 17.2 times basal). Interestingly, (-)YM796 did not show significant inhibition of cAMP formation in M2LKB2-2 cells except at extremely high concentrations (greater than 1mM). (+)YM796 exhibited no significant efficacy for the M1 and M2 muscarinic receptors. These results suggest that (-)YM796 represents a muscarinic partial agonist with functional selectivity for the M1 muscarinic receptors whereas (+)YM796 shows no efficacy for either M1 or M2 muscarinic receptors in these transfected cells.

The m2 muscarinic acetylcholine receptors are coupled to multiple signaling pathways via pertussis toxin-sensitive guanine nucleotide regulatory proteins

The muscarinic m1 and m2 receptors are functionally coupled to multiple effectors via distinct guanine nucleotide regulatory proteins (G-proteins) defined by their pertussis toxin (PTX) sensitivity. Both receptors are coupled to the hydrolysis of phosphoinositides (PI), whereas only the m2 receptors inhibit cAMP formation. This study examines how the selective interactions of these two receptors with G-proteins may govern their specific functional coupling to the two second messenger pathways. Murine fibroblasts (B82) transfected with the rat m1 or m2 receptor genes were used to test the PTX sensitivity of the m1 and m2 receptor-mediated pathways. It was found that the stimulation of PI hydrolysis and inhibition of cyclic AMP mediated by m2 receptors had similar PTX sensitivity (IC50 = 0.14 ng/ml and 0.26 ng/ml), whereas the m1-mediated PI hydrolysis was PTX insensitive. The EC50 value for carbachol in the m1 receptor-mediated PI hydrolysis was 9.5 microM, whereas those for the m2 receptor-mediated PI hydrolysis and inhibition of cyclic AMP formation were 0.3 microM and 1.2 microM, respectively. The potency of carbachol correlated well with its binding affinities for the two receptor subtypes. These results suggest that the m2 receptors are coupled to multiple pathways via PTX-sensitive G-proteins, which are distinct from those that interact with the m1 receptor. The formation of functional receptor-G-protein complexes may be selective and governed by the efficiencies in coupling between receptors and G-proteins.

Characterization of a tachykinin peptide NK2 receptor transfected into murine fibroblast B82 cells

Membranes isolated from a murine fibroblast B82 cell line (SKLKB82#3) transfected with the bovine stomach cDNA pSKR56S exhibited binding of [His(125I)1]neurokinin A (125I-NKA) to a single population of sites with a Bmax of 147 fmol/mg of protein and a Kd of 0.59 nM. Control cell lines had little or no specific binding. The ligand binding in SKLKB82#3 cells was reversible and was inhibited by peptides in the potency rank of neuropeptide gamma greater than neuropeptide K greater than neurokinin A greater than [10-norleucine]neurokinin A-(4-10) greater than substance P much greater than senktide (succinyl-Asp-Phe-MePhe-Gly-Leu-Met-NH2). Specific binding was enhanced by Mn2+, Mg2+, and Ca2+ and was inhibited by guanine nucleotide analogues. Thus, SKLKB82#3 cells have been transfected with NK2 receptors that have become associated with an endogenous guanine nucleotide-binding protein. In comparison with membranes from the hamster urinary bladder, a tissue enriched in NK2 receptors, NK2 receptor antagonists displayed markedly different potencies, either more or less potent, in inhibiting specific binding in membranes of the transfected cells. Furthermore, inhibition of 125I-NKA binding by nucleotide analogues was markedly different in SKLKB82#3 cells compared with hamster bladder tissue. The different binding profile in the cells is not due to an artefact introduced during cDNA transfection because a similar profile was also observed in bovine stomach membranes. These results may indicate the existence of two distinct NK2 receptors.

Pharmacologic comparison of selected agonists for the M1 muscarinic receptor in transfected murine fibroblast cells (B82)

The radioligand binding and functional properties of 10 muscarinic agonists for the M1 muscarinic receptors were characterized on the murine fibroblast B82 cells, which have been transfected with the m1 gene. All of the muscarinic agonists completely inhibited [3H](-)methyl-3-quinuclidinyl benzilate binding to the M1 muscarinic receptor in the transfected B82 cells. Their apparent inhibition constant values for agonist/[3H](-)methyl-3-quinuclidinyl benzilate inhibition experiments correlate well with their EC50 values in stimulating phosphatidylinositide hydrolysis. Based on the maximal functional effects: (+)-cismethyl-dioxolane, oxotremorine-M, acetylcholine, carbachol and methacholine are most efficacious, McN-A-343 and arecoline are least efficacious, whereas the efficacies of oxotremorine and pilocarpine are intermediate. In addition, McN-A-343 inhibited carbachol-stimulated phosphatidylinositide hydrolysis. Spare receptors were detected for oxotremorine-M, methacholine and carbachol, but not the rest of the agonists, by comparing the receptor-occupancy curves with the concentration-response curves. These results suggest that the presence of a quaternary nitrogen (trimethylammonium group) within the structure of the agonist may be important for the expression of full agonist activity.

Ab initio study of the electrostatic multipole nature of torsional potentials in CH3SSCH3, CH3SSH, and HOOH

The origin of torsional potentials in H3CSSCH3, H3CSSH, and HOOH and the anisotropy of the local charge distribution has been analyzed in terms of atomic multipoles calculated from the ab initio LCAO-MO-SCF wave function in the 6-31G* basis set. The results indicate that for longer -S-S-bonds the major contribution to these torsional barriers are electrostatic interactions of the atomic multipoles located on two atoms forming the rotated bond. This finding demonstrates the important role of electrostatic 1-2 interatomic interactions, usually neglected in conformational studies. It also opens the possibility to derive directly from accurate ab initio wave functions a simple nonempirical torsional potential involving atomic multipoles of two bonded atoms defining the torsional angle. For shorter -O-O- bonds, use of more precise models and inclusion of 1-3 interactions seems to be necessary.