Differential expression of human high-molecular-weight salivary mucin (MG1) and low-molecular-weight salivary mucin (MG2)

Two distinct mucin components of saliva, MG1 and MG2, have been identified based on chemical composition and molecular weights (high and low, respectively) in saliva. With the aim of characterizing the expression pattern of salivary mucins, we have prepared monoclonal antibodies (MAbs) directed against the peptide core of MG1 and against a synthetic peptide derived from the MG2 (MUC7) sequence. MAb PANH2 raised against partially deglycosylated MG1 stained a high-molecular-weight smear in Western blots of partially purified MG1. PANH2 binding was increased by deglycosylation with trifluoromethanesulfonic acid as well as with subsequent periodate treatment, and was eliminated by pronase treatment, strongly suggesting that MAb PANH2 was directed to a peptide epitope of MG1. MAb PANH3 raised against a synthetic peptide derived from the MG2 (MUC7) sequence reacted with the native molecule and stained a narrow smear of ca. 200,000 to 210,000 in Western blots of concentrated saliva and a lower-molecular-weight smear of trifluoromethanesulfonic-acid-treated MG2. Immunohistology on frozen sections of human salivary glands showed that MAb PANH2 selectively labeled mucous cells, whereas MAb PANH3 labeled subpopulations of serous cells. Double-direct immunofluorescence staining with PANH2 and PANH3 demonstrated that the staining patterns were non-overlapping. The development of these antibody probes will facilitate studies of mucin expression in diseases of salivary glands.     

Specific detection of sialyl Lewis X determinant carried on the mucin GlcNAcbeta1-->6GalNAcalpha core structure as a tumor-associated antigen

Sialyl Lewis X serves as a ligand for selectins and is proposed to be implicated in hematogenous metastasis of cancers. When a cultured human breast cancer cell line, MCF-7, which does not express sialyl Lewis X, was transfected with human fucosyltransferase VI cDNA, a strong expression of sialyl Lewis X was induced on transfectant cells. The transfectant cells were found to be also reactive to the antibody NCC-ST-439, which was initially raised against human gastric cancer cells and later was shown to recognize a tumor-associated carbohydrate antigen in breast, gastric, and colon cancers. This suggested that the antigen recognized by NCC-ST-439 is closely related to sialyl Lewis X. Subsequent studies indicated that NCC-ST-439 specifically reacts to NeuAcalpha2-->3Galbeta1-->4(Fucalpha1-->3)GlcNAcbet a1-->6GalNAcalpha1 -->R, the sialyl Lewis X on the mucin GlcNAcbeta1-->6 GalNAcalpha structure. The antibody was not reactive to the conventional sialyl Lewis X determinants on straight and/or branched polylactosamine structures including NeuAcalpha2-->3Galbeta1-->4(Fucalpha1-->3)GlcNAcbet a1-->3Galbeta1-->4 Glcbeta1-->R and NeuAcalpha2-->3Galbeta1-->4(Fucalpha1-->3)GlcNAcbet a1-->6Galbeta1-->4 Glcbeta1-->R. This was in clear contrast to most of the known anti-sialyl Lewis X antibodies, which do not discriminate internal structures carrying the sialyl Lewis X determinant. On the other hand, the newly generated monoclonal antibody GSC154-27 had a specificity completely the reverse of the specificity of NCC-ST-439 in that it was strongly reactive to the conventional sialyl Lewis X determinants in straight and branched polylactosamine structures, while far less reactive to the sialyl Lewis X determinant on the mucin GlcNAcbeta1-->6GalNAcalpha core structure. A set of these two antibodies would be useful in discriminating the molecular species of sialyl Lewis X expressed by malignant cells and in studying their functional significance.     

Identification of a major carbohydrate capping group of the L-selectin ligand on high endothelial venules in human lymph nodes as 6-sulfo sialyl Lewis X

We investigated the molecular species of sulfated sialyl Lewis X determinants, the putative L-selectin ligand, expressed on high endothelial venules (HEV) in human lymph nodes. Comparison of the reactivity pattern of HEV with the reactivity of the pure 6-sulfo, 6'-sulfo, or 6,6'-bissulfo sialyl Lewis X determinant with hitherto known anti-sialyl Lewis X antibodies strongly suggested 6-sulfo sialyl Lewis X to be the best candidate for the major sulfated sialyl Lewis X determinant on HEV, followed by 6,6'-bissulfo sialyl Lewis X, whereas 6'-sulfo sialyl Lewis X was unlikely. We newly generated monoclonal antibodies (mAbs) G152 and G72 directed against 6-sulfo sialyl Lewis X, which intensely labeled HEV in immunohistochemical examination and inhibited binding of recombinant L-selectin-IgG to HEV, suggesting that the determinant serves as a ligand for L-selectin. To test the concomitant expression of 6, 6'-bissulfo sialyl Lewis X, specific mAbs (G2706, G27011, G27037, and G27039) were generated, but all antibodies failed to react to HEV. Next, we established mAbs (AG97 and AG273) directed against 6-sulfo Lewis X, the asialo form of 6-sulfo sialyl Lewis X. The antibodies were not reactive to untreated HEV, but strongly reacted to sialidase-treated HEV. This indicated the predominance of the sialylated form of 6-sulfo sialyl Lewis X and minimal expression of its asialo form, corroborating that it was synthesized by fucosyltransferase VII, the isoenzyme that preferentially produces the sialylated form of the determinant.     

Sulfated sialyl Lewis X, the putative L-selectin ligand, detected on endothelial cells of high endothelial venules by a distinct set of anti-sialyl Lewis X antibodies

Endothelial cells of high endothelial venules (HEV) in human peripheral lymph nodes expressed a distinct type of sialyl Lewis X antigen, which was detected preferentially with a set of anti-sialyl Lewis X antibodies, 2F3, 2H5 and HECA-452 in immunohistochemistry, while another set of anti-sialyl Lewis X antibodies, FH-6 and CSLEX-1, failed to detect it. The adhesion of cells expressing L-selectin to HEV was inhibited by members of the former set of antibodies in Stamper-Woodruff assays performed on frozen sections of human peripheral lymph nodes. Transfection of a cultured endothelial cell line with a human alpha1-->3 fucosyltransferase, Fuc-T VII, resulted in the expression of a distinct type of sialyl Lewis X antigen having the reactivity similar to that of HEV; i.e., the antigen appearing on the transfectant clone was detectable only with the set of 2F3, 2H5 and HECA-452, but not with the set of FH-6 and CSLEX-1. Treatment of transfectant cells with sodium chlorate, a metabolic inhibitor of sulfation, resulted in reactivity to the members of the latter set of antibodies, suggesting that sulfation of sialyl Lewis X moiety was the cause of the discrepancy in the reactivity of the anti-sialyl Lewis X antibodies. When tested against various authentic sulfated sialyl Lewis X determinants, 6-sulfo sialyl Lewis X and 6,6'-bis-sulfo sialyl Lewis X were found to be reactive to the antibodies, 2F3, 2H5 and HECA-452, but not with antibodies FH-6 and CSLEX-1, suggesting that the distinct type of sialyl Lewis X determinant on the HEV endothelial cells and Fuc-T VII-transfected endothelial cell clone are mainly 6-sulfo and/or 6,6'-bis-sulfo sialyl Lewis X determinants.     

Structural features of the human salivary mucin, MUC7

Specific mgi mutations in the alpha, beta or gamma subunits of the mitochondrial F1-ATPase have previously been found to suppress rho0 lethality in the petite-negative yeast Kluyveromyces lactis. To determine whether the suppressive activity of the altered F1 is dependent on the F0 sector of ATP synthase, we isolated and disrupted the genes KlATP4, 5 and 7, the three nuclear genes encoding subunits b, OSCP and d. Strains disrupted for any one, or all three of these genes are respiration deficient and have reduced viability. However a strain devoid of the three nuclear genes is still unable to lose mitochondrial DNA, whereas a mgi mutant with the three genes inactivated remains petite-positive. In the latter case, rho0 mutants can be isolated, upon treatment with ethidium bromide, that lack six major F0 subunits, namely the nucleus-encoded subunits b, OSCP and d, and the mitochondrially encoded Atp6, 8 and 9p. Production of rho0 mutants indicates that an F1-complex carrying a mgi mutation can assemble in the absence of F0 subunits and that suppression of rho0 lethality is an intrinsic property of the altered F1 particle.     

Biophysical approaches to salivary mucin structure, conformation and dynamics

Our understanding of the origins of the physical and biochemical properties of mucous glycoproteins is incomplete and not with out controversy. Recent molecular biological and biophysical studies revealing the architecture and solution structure and dynamics of a series of salivary mucins, invaluable toward resolving many of these questions, are discussed. Mucins are very large, structurally heterogeneous, and highly expanded molecules with the carbohydrate playing a key role in maintaining the extended mucin conformation.     

Human intestinal M cells display the sialyl Lewis A antigen

The biochemical features that distinguish human M cells from other intestinal epithelial cell types are important for understanding microbial pathogenesis and for targeting vaccines to the mucosal immune system. We applied a large panel of carbohydrate-specific monoclonal antibodies and lectins to Peyer's patch and cecum biopsy specimens from three normal individuals and a patient with inflammatory bowel disease. The results show that human M-cell glycosylation patterns are distinct from those of other species examined and that human M cells preferentially display the sialyl Lewis A antigen. This carbohydrate epitope is also present in a small subpopulation of enterocytes in the follicle-associated epithelium and in goblet cell mucins.     

Binding of the pili of Pseudomonas aeruginosa to a low-molecular-weight mucin and neutral cystatin of human submandibular-sublingual saliva

The HLA-B*27 group of alleles has been extensively studied due to the association of particular B*27 alleles with ankylosing spondylitis (AS). We describe here an HLA-B*27 allele (B*2712) encoding an antigen that lacks reactivity with B27 monoclonal antibodies (moabs) and alloantisera but reacts with some B40/B60 moabs and alloantisera and expresses the Bw6 public epitope. This allele was discovered by the segregation of an HLA-B allele undetectable by PCR-SSP within a Caucasian family from the British population referred for routine bone marrow transplant HLA typing and found in the haplotype A*29; B*2712; Cw*1203; DRB1*13; DQB1*0603. Serological typing showed a lack of reactivity with four B27 moabs and four alloantisera but positive reactivity with moabs and alloantisera specific for B40/B60 and Bw6 public epitopes. Subsequent sequencing showed the closest homology was with B*2708 with three mismatches in exon 2 at positions 204, 209 and 210. The intron 2 sequence was identical with other B*27 lineage alleles including a 2 base pair deletion at positions 95 and 96. The relationship between HLA-B*2712 and reported B60 associations with susceptibility to AS remains to be determined.     

The kinetics and shear threshold of transient and rolling interactions of L-selectin with its ligand on leukocytes

The kinetics of rolling and transient adhesions through selectins may depend on the kinetics and mechanical properties of the selectin:ligand bond, as well as on cellular properties including receptor-anchoring to the cell membrane and cytoskeleton. Kinetics are known to depend on the selectin and may also be ligand dependent. Here, we study the kinetics of transient and rolling interactions of leukocytes with L-selectin immobilized on a substrate. Remarkably, all properties examined are similar to those seen when the sidedness is opposite, i.e., when the L-selectin ligand is on the substrate and when the ligand is isolated from HEV rather than present on leukocytes. The similar properties include rolling velocity, a threshold shear stress above 0.4 dyn/cm2 required to support rolling, a k degreesoff of 7.0 to 6.8 s-1 for the L-selectin tether bond, and a mechanical bond length of 0.24 to 0.20 A. Our results argue against a model in which L-selectin shedding mediates rolling. Furthermore, the fast and force-resistant kinetic properties suggest that L-selectin is specialized dynamically for tethering leukocytes to vessel walls and adherent leukocytes.     

Measurement of sialyl transferase activity and serum glycoproteins in malignant and beningn (hyperparathyroid) hypercalcemia

Serum sialyl tranferase activity (STA) and protein bound carbohydrate were measured in hypercalcemic patients with surgically documented hyperparathyroidism (n = 15) or with cancer without skeletal metastases (n = 10). Precipitable protein-bound sialic acid and hexosamine, but not neutral hexoses or fucose were significantly (P less than 0.025) increased 40% and 21% respectively, in the perchlorate treated sera of cancer patients. Measurements of some specific serum glycoproteins by radial immunodiffusion assay were also different (P less than 0.05). Mean seromucoid protein was almost twice as great in the group with cancer (P less than 0.005), but four of these values overlapped those from the patients with hyperparathyroidism. The mean STA was 21.1 (range, 9.0-46.8) activity units in the patients with the cancer and 9.2 (range 1.0-17.8) in the patients with hyperparathyroidism (P less than 0.005). Six of the patients with cancer had values above the upper limit of the group with hyperparathyroidism. A discriminant function generated from these data correctly classified all the patients with hyperparathyroidism and 70% of those with cancer. Measurements of seromucoid and STA deserve further consideration as a way to discriminate some cases of hypercalcemia.     

Human papillomavirus genotype as a major determinant of the course of cervical cancer

PURPOSE: To determine whether the prognosis of invasive cancers of the uterine cervix is related to the type of human papillomavirus (HPV) associated with the tumor. PATIENTS AND METHODS: Two hundred ninety-seven patients with invasive cervical cancer were prospectively registered from 1986 to 1994. HPV typing was performed on DNA extracted from frozen tumor specimens by means of Southern blot hybridization (SBH) and polymerase chain reaction (PCR) techniques. The median follow-up was 38 months. RESULTS: HPV sequences were detected in 246 patients (83%): 150 patients had HPV16, 31 patients had HPV18, and 14 patients had one of the intermediate-oncogenic-risk HPV types (HPV31, 33, 35, 52, 58). In 51 patients, HPV type remained undetermined, and in 51 patients, no viral sequences were found. No significant associations were observed between virologic data and tumor stage or node status. The 5-year disease-free survival (DFS) rate was 100% for patients with intermediate-risk HPV-associated tumors, 58% for patients with HPV16-positive tumors, and 38% for patients with HPV18-positive tumors (P = .02). In multivariate analysis, patients with HPV18-associated tumors had a relative risk (RR) of death 2.4 times greater (95% confidence interval [CI], 1.29-4.59) than that for patients with HPV16, and 4.4 times greater (95% CI, 3.48-5.32) than that for patients with a tumor associated with a viral type different from HPV16/18. CONCLUSION: The prognosis for invasive cancers of the uterine cervix is dependent on the oncogenic potential of the associated HPV type. HPV typing may provide a prognostic indicator for individual patients and is of potential use in defining specific therapies against HPV-harboring tumor cells.     

Molecular cloning, sequence, and specificity of expression of the gene encoding the low molecular weight human salivary mucin (MUC7)

Previous biochemical studies have determined that human saliva contains high and low molecular weight mucin glycoproteins (MG1 and MG2, respectively) that are structurally distinct. In this study, we describe the isolation and characterization of overlapping cDNA clones which code for the MG2 protein core. DNA sequencing revealed a translated region of 1131 nucleotides encoding a protein of 377 amino acid residues with a molecular mass of 39 kDa. The first 20 N-terminal residues were very hydrophobic and probably comprise the MG2 leader peptide. The region encoding the secreted protein can be divided into three distinct domains; unique 5'- and 3'-translated regions containing 4 and 1 potential N-glycosylation sites, respectively, and a central region of six almost perfect tandem repeats of 23 amino acid residues with a high number of Thr and Ser. No sequence homology with any other human or animal mucins, and no significant homology to any other proteins was found. MG2 mRNA is about 2.5 kilobases long, and its expression appears to be species-, tissue-, and cell-specific. We propose to name this gene MUC7 in accordance with the mucin genes cloned to date named MUC1-MUC6.     

Sigma ligand S14905 and locomotor activity in mice

The binding and locomotor profile of a new sigma ligand, S14905, (isobutyl-N-(1-indan-2yl-piperid-4-yl)N-methyl carbamate, furamate) was studied. The binding data revealed that S14905 has a high affinity for sigma receptors and very low affinity for both dopamine D1 and D2 receptors. We have demonstrated that this sigma ligand prevents the locomotor stimulation induced by morphine (32 and 64 mg/kg), cocaine (16 mg/kg), amphetamine (4 mg/kg) and adrafinil (32 mg/kg) at doses lower than those required to depress spontaneous locomotor activity. The antagonism observed in the present study seems to be more specific of morphine induced hyperlocomotion. The high affinity of this compound for sigma receptors makes it a good choice to study the role of this receptor in the CNS. In addition, S14905 does not directly block dopamine receptors but may modulate them in some manner, and would thus warrant further study as a potential atypical antipsychotic agent, and an antagonist for the hyperactivity induced by opiate drug.     

P-Selectin support of neonatal neutrophil adherence under flow: contribution of L-selectin, LFA-1, and ligand(s) for P-selectin

To further define the neonatal neutrophil's ability to localize to inflamed tissue compared with adult cells, we examined the neonatal neutrophil interactions with P-selectin monolayers under two conditions: (1) attachment under constant shear stress and flow and (2) detachment where cells were allowed to attach in the absence of shear stress and then shear stress is introduced and increased in step-wise increments. Cord blood and adult neutrophils had minimal interactions with unstimulated human umbilical vein endothelial cells (HUVECs) at a constant shear stress of 2 dynes/cm2. There was a marked increase in the number of both neonatal and adult cells interacting (interacting cells = rolling + arresting) with HUVECs after histamine stimulation, although the neonatal value was only 40% of adult (P < .05). Neonatal neutrophils also had significantly decreased interaction with monolayers of Chinese hamster ovary (CHO) cells transfected with human P-selectin (CHO-P-selectin; 60% of adult values, P < .003). Of the interacting cells, there was a lower fraction of neonatal cells that rolled compared with adult cells on both stimulated HUVECs and CHO-P-selectin. That neonatal neutrophil L-selectin contributes to the diminished attachment to P-selectin is supported by the following: (1) Neonatal neutrophils had significantly diminished expression of L-selectin. (2) Anti-L-selectin monoclonal antibody reduced the number of interacting adult neutrophils to the level seen with untreated neonatal neutrophils, but had no effect on neonatal neutrophils. In contrast, L-selectin appeared to play no role in maintaining the interaction of either neonatal or adult neutrophils in the detachment assay. Once attachment occurred, the neonatal neutrophil's interaction with the P-selectin monolayer was dependent on LFA-1 and to other ligands to a lesser degree based on the following: (1) Control neonatal neutrophils had decreased rolling fraction compared with adult neutrophils, although the total number of interacting neutrophils was equal between groups. (2) Anti-LFA-1 treatment resulted in an increase in the rolling fraction of both neonatal and adult neutrophils. However, whereas the number of interacting adult neutrophils remained unchanged, the number of neonatal neutrophils decreased with increased shear stress. We speculate that this increased detachment of neonatal cells is due to differences in neutrophil ligand(s) for P-selectin.     

The high-molecular-weight human mucin is the primary salivary carrier of ABH, Le(a), and Le(b) blood group antigens

Because many bacteria interact with the carbohydrate portions of receptor molecules, factors controlling glycosylation probably influence the ability of salivary components to mediate bacterial adherence/clearance. Important sources of diversity in glycosylation are the ABO, secretor, and Lewis genes, which code for glycosyltransferases that add specific sugar sequences to the termini of carbohydrate chains of glycolipids and glycoproteins. We identified, by Western blotting, salivary glycoproteins carrying the ABH and Le(a) or Le(b) antigens. Samples of whole, unstimulated saliva were obtained from 19 subjects whose blood group was determined by agglutination of red blood cells with specific antisera. After centrifugation, the samples were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and blotted onto nitrocellulose. Glycoproteins carrying blood group antigens were identified by staining the blot with monoclonal antisera specific for the A, B, H, Le(a), or Le(b) antigens. The most intensely staining component from all the samples migrated at the same position as the high-molecular-weight mucin. Saliva samples from the nonsecretors contained only the Le(a) antigen. Samples from the secretors contained one or more of the ABH antigens and, variably, the Le(b) antigen. In all cases, the salivary blood group antigens corresponded to those found on the red blood cells of the same subject. The functional consequences of the expression of blood group antigens on the high-molecular-weight mucin are not known, but their presence could modulate the adherence of certain oral microorganisms that interact preferentially with this molecule.     

Human mucin genes assigned to 11p15.5: identification and organization of a cluster of genes

Four distinct genes that encode mucins have previously been mapped to chromosome 11p15.5. Three of these genes (MUC2, MUC5AC, and MUC6) show a high level of genetically determined polymorphism and were analyzed in the CEPH families. Linkage analysis placed all three genes on the genetic map in a cluster between HRAS and INS, and more detailed analysis of recombinant breakpoints revealed that MUC6 is telomeric to MUC2. Using these recombinants D11S150 was mapped close to MUC2. Ten of the 11 recombinant chromosomes studied in detail were paternal, and the recombinant events were distributed throughout the 11p15 region, suggesting that the high level of recombination observed in 11p15.5 is not due to a particular recombinational hot spot. Pulsed-field gel electrophoresis was used to make a detailed physical map of the MUC cluster and to integrate the physical and genetical maps. The gene order was determined to be HRAS-MUC6-MUC2-MUC5AC-MUC5B-IGF2. The MUC genes span a region of some 400 kb and the map extends 770 kb and contains 15 putative CpG islands. The order of the MUC genes on the map corresponds to the relative order of their expression along the anterior-posterior axis of the body, suggesting a possible functional significance to the gene order.     

L-selectin binds to P-selectin glycoprotein ligand-1 on leukocytes: interactions between the lectin, epidermal growth factor, and consensus repeat domains of the selectins determine ligand binding specificity

The selectins mediate cellular interactions by binding carbohydrate determinants present on a limited number of glycoprotein ligands. L-selectin binds multiple ligands expressed on endothelial cells, while P-selectin interacts exclusively with P-selectin glycoprotein ligand-1 (PSGL-1) on leukocytes. In this study, L-selectin was shown to bind leukocytes through the P-selectin ligand, PSGL-1, although at lower levels than P-selectin. L-selectin binding to PSGL-1 is specific since it was blocked by Abs to L-selectin or PSGL-1, required appropriate glycosylation of PSGL-1, and was Ca2+ dependent. The contributions of the extracellular domains of the selectins to ligand binding was assessed using a panel of chimeric selectins created by exchange of domains between L-selectin and P- or E-selectin. The lectin and epidermal growth factor domains of L- and P-selectin contributed significantly to binding through similar, if not identical, regions of PSGL-1. The different chimeric selectins revealed that the lectin domain was the dominant determinant for ligand binding, while cooperative interactions between the lectin, epidermal growth factor, and short consensus repeat domains of the selectins also modified ligand binding specificity. L-selectin binding to PSGL-1 expressed by leukocytes may mediate neutrophil rolling on stationary leukocytes bound to cytokine-induced endothelial cells, which was previously reported to be a L-selectin-dependent process.     

Relationship between cleaved L-selectin levels and the outcome of acute myeloid leukemia

High plasma levels of the shed form of L-selectin (sL-selectin) are frequently detectable in acute myeloid leukemia (AML). sL-selectin can inhibit blast cell adhesion to vascular endothelium and may thereby influence the phenotype of AML. In this study, we have investigated the relationship between sL-selectin levels and clinical presentation or disease outcome in 100 patients with AML. Fifty-eight patients were found to have sL-selectin levels >/=3.12 microgram/mL (>/=3 SD above the mean of healthy controls: "increased"). Patients with extramedullary disease such as lymphadenopathies, splenomegaly, hepatomegaly, and/or muco-cutaneous infiltration had significantly increased sL-selectin levels (P < .001). sL-selectin levels were significantly heterogeneous in the French-American-British subtypes (P = .0003). Patients with "normal" sL-selectin levels had higher probability of achieving complete remission (CR) than with "increased" levels: 81% versus 64%, respectively (P = .06). When adjusting for clinically relevant covariates predictive for CR (sex, age, Auer rods), "normal" sL-selectin levels were significantly associated with CR (odds ratio, 3.08; 95% confidence interval [CI], 1.10 to 8.58; P = .03). Moreover, patients with "increased" sL-selectin levels (>/=3.12 microgram/mL) had shorter event-free survival (EFS) (median 7.3 v 12 months, P = .008) and overall survival (median 1 v 2.05 years, P = .03) than patients with sL-selectin <3.12 microgram/mL. Multivariate statistical analysis (adjusted for age and presence of Auer rods) indicated that sL-selectin was an independent prognostic factor for EFS (hazard ratio [HR], 1.96; 95% CI, 1.21 to 3.17, P = .006) and overall survival (HR, 1.80; 95% CI, 1.09 to 2.98; P = .02). Thus, plasma sL-selectin may be a useful prognostic marker in the evaluation of AML at diagnosis.     

Sevoflurane has less effect than halothane on pulmonary afferent activity in the rabbit

We have compared the effects of sevoflurane and halothane on the discharge frequencies of 19 slowly adapting and four rapidly adapting lung receptors in the rabbit by recording from single vagal fibres. Both agents reduced the discharge frequency of slowly adapting receptors during expiration (P < 0.0005), halothane having a greater effect than sevoflurane (P < 0.0005). Neither agent had any effect on discharge frequency at the end of inspiration when discharge frequency is at a maximum. Neither agent affected the discharge frequency of rapidly adapting receptors.     

Protein kinase domain of twitchin has protein kinase activity and an autoinhibitory region

Twitchin is a 753-kDa polypeptide located in the muscle A-bands of the nematode, Caenorhabditis elegans. It consists of multiple copies of both fibronectin III and immunoglobulin C2 domains and, near the C terminus, a protein kinase domain with greatest homology to the catalytic domains of myosin light chain kinases. We have expressed and purified from Escherichia coli twitchin's protein kinase catalytic core and flanking sequences that do not include fibronectin III and immunoglobulin C2 domains. The protein was shown to phosphorylate a model substrate and to undergo autophosphorylation. The autophosphorylation occurs at a slow rate, attaining a maximum at 3 h with a stoichiometry of about 1.0 mol of phosphate/mol of protein, probably through an intramolecular mechanism. Sequence analysis of proteolytically derived phosphopeptides revealed that autophosphorylation occurred N-terminal to the catalytic core, predominantly at Thr-5910, with possible minor sites at Ser5912 and/or Ser-5913. This portion of twitchin (residues 5890-6268) was also phosphorylated in vitro by protein kinase C in the absence of calcium and phosphotidylserine, but not by cAMP-dependent protein kinase. By comparing the activities of three twitchin segments, the enzyme appears to be inhibited by the 60-amino acid residues lying just C-terminal to the kinase catalytic core. Thus, like a number of other protein kinases including myosin light chain kinases, the twitchin kinase appears to be autoregulated.