Characterization of immunoreactive motilin from the rat small intestine

Immunocytochemistry, radioimmunoassay, chromatography, and biological assay using a rabbit isolated duodenal muscle strip preparation were used in attempting to characterize motilin from the rat small intestine. Several different antisera and monoclonal antibodies directed against natural porcine motilin were used. A variety of fixation techniques using Bouin's, paraformaldehyde, and benzoquinone with different staining methods including, fluorescein-conjugated second antibody, peroxidase-antiperoxidase or peroxidase-conjugated second antibody techniques were used. All methods failed to detect immunoreactive motilin cells in the rat small intestine. The same antisera were used in radioimmunoassays for motilin to evaluate extracts of rat intestinal tissue. Two of these detected immunoreactive motilin in gut extracts, and these antisera showed a different distribution for the peptide. Samples containing immunoreactive motilin obtained from cation exchange chromatography on SP-Sephadex-G25 were concentrated and assayed for biological activity in a rabbit duodenal muscle strip preparation. Desensitization of duodenal tissue to porcine motilin could be demonstrated by pretreatment with this peptide. The biological activity of partially purified rat intestinal immunoreactive motilin was not prevented by pretreatment of the tissue with motilin. Further purification of this preparation on Bio-Gel P-10 yielded an immunoreactive motilin peak that co-eluted with natural porcine motilin. Rat intestinal immunoreactive motilin did not co-elute with natural porcine motilin following high pressure liquid chromatography on a Waters microBondapak C18 reversed-phase column using a linear gradient of water-acetonitrile (10-45%) over 30 min. Although of similar molecular size, rat motilin is probably structurally dissimilar to other mammalian motilins.

Do thin filaments of smooth muscle contain calponin? A new method for the preparation

A new method for the preparation of smooth muscle thin filaments which include calponin was established. We found that calponin readily separated from thin filaments in the presence of 10 mM ATP. By preventing thin filament extract from exposing to ATP, we obtained thin filaments which contained actin, tropomyosin, caldesmon and calponin in molar ratios of 7:0.9:0.6:0.7. We studied myosin Mg-ATPase activity by using the thin filaments in comparison with classical thin filaments prepared by the method of Marston and Smith, which contained the same amounts of caldesmon and tropomyosin as our thin filaments but lost almost all calponin. The presence of calponin reduced the Vmax value for thin filament-activated myosin Mg-ATPase activity by 33% without a significant change in Km value. These findings suggest that calponin inhibits myosin Mg-ATPase activity by modulation of a kinetic step as an integral component of smooth muscle thin filaments.

Distinct vascular and intestinal smooth muscle myosin heavy chain mRNAs are encoded by a single-copy gene in the chicken

We examined whether the gizzard MHC gene is expressed in other smooth muscle tissues and, if so, whether there exist any smooth muscle MHC isoforms at the mRNA level. Northern blot analysis showed that the gizzard MHC gene was also expressed in the aorta and jejunum, but not in the pectoralis muscle or in fibroblasts. This indicates that striated muscle and non-muscle MHC isoforms are encoded in genes distinct from the smooth muscle MHC gene. Further, nuclease S1 mapping showed that the aortic smooth muscle MHC mRNA was distinct from the gizzard mRNA in the 5'-terminal coding region. Both of these mRNA species are expressed in the jejunum. These observations suggest that there exist at least two chicken smooth muscle MHC isoforms, vascular-type and intestinal-type, and that these isoforms are generated from a single-copy gene, probably by an alternative mRNA processing mechanism.

Solubilization of a 5-HT3 binding site from rabbit small bowel muscularis membranes

A 5-HT3 binding site, with high affinity for (S-)[3H]zacopride, was solubilized from rabbit small bowel muscularis membranes utilizing 0.5% sodium cholate and 400 mM (NH4)2SO4. Approximately 72% of the (S-)[3H]zacopride binding activity was recovered in a form that retained the high affinity (Kd = 0.7 nM) and specificity for this radioligand that is characteristic of the membrane-bound receptor. ICS 205-930 and other 5-HT3 compounds were effective inhibitors and exhibited the same rank order of potency in the solubilized and membrane-bound preparations. The receptor-detergent complex did not sediment after centrifugation for 1 h at 150,000 x g and eluted between thyroglobulin (MW = 669,000) and apoferritin (MW = 443,000) when fractionated by high-performance liquid chromatography gel filtration. This is the first report of the solubilization of a 5-HT3 binding site.

Gaucher's disease type I. Report of a case with prominent deposition of ceroid in splenic endothelial cells and intestinal smooth muscle fibers

A case of type I Gaucher's disease in a 39-year-old male is reported. Autopsy showed marked enlargement of the spleen (3,070 g) and infiltration of typical Gaucher's cells in the spleen, liver, bone, marrow, gastrointestinal tract, lymph nodes and adrenal glands. The diagnosis of Gaucher's disease was ascertained by the very low beta-glucosidase activity of cultured subcutaneous fibroblasts and the high content of glucocerebroside in the spleen tissue. A peculiar finding in this case was prominent deposition of brown pigment in endothelial cells of the spleen and smooth muscles fibers of the gastrointestinal tract, urinary bladder and prostate. Histochemical examination revealed that the granules in endothelial cells and smooth muscle fibers were ceroid. Such deposition of ceroid has never been reported previously in Gaucher's disease. Ceroid deposition in generalized smooth muscle fibers is known as brown bowel syndrome, and is highly suggestive of severe vitamin E deficiency. Although other symptoms of vitamin E deficiency were not noticed in this case, some malnutritional condition might play a role in prominent deposition of ceroid in lysosomes, possibly together with deficient activity of a lysosomal enzyme.

Gallbladder CCK receptors: species differences in glycosylation of similar protein cores

Receptors for cholecystokinin (CCK) on gallbladder muscularis smooth muscle have different apparent sizes in man (Mr = 85,000-95,000) and cow (Mr = 70,000-85,000). In this work, these receptors were demonstrated to represent N-linked complex glycoproteins with Mr = 43,000 protein cores, based on lectin-affinity chromatography and the deglycosylation of bands affinity labeled with 125I-D-Tyr-Gly-[(Nle28,31, pNO2-Phe33)CCK-26-33] using neuraminidase, O-glycanase and endoglycosidases H and F. Similarities in the core proteins were further demonstrated by Staphylococcus aureus V8 protease peptide mapping, in which both proteins yielded similar fragment patterns. Thus, gallbladder CCK receptors present in man and cow are both N-linked complex glycoproteins, with different carbohydrate domains and similar protein cores.

Immunofluorescence localization of vinculin in ectoplasmic ("junctional") specializations of rat Sertoli cells

We have investigated, using indirect immunofluorescence techniques, the possibility that vinculin is a component of Sertoli cell ectoplasmic specializations. Affinity-purified polyclonal antibodies produced against human platelet vinculin were used to probe fixed frozen sections of rat testis. Specific fluorescence occurs in Sertoli cell regions adjacent to spermatids and to basally situated junctional complexes, sites at which ectoplasmic specializations are known to occur. Staining also occurs in Sertoli cell regions associated with tubulobulbar complexes. The antibody also labels focal contacts in cultured human dermal fibroblasts, apical junctional sites of rat epididymal epithelium, and dense plaques of smooth muscle. Our results are consistent with the prediction that vinculin is likely a component of ectoplasmic specializations and are also consistent with the hypothesis that these structures are a form of actin-associated adhesion complex.

Isolation and characterization of calcium binding glycoproteins of cardiac sarcolemmal vesicles

Two major Ca2(+)-binding glycoproteins Mr 120,000 and 100,000 were isolated from 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid -solubilized bovine heart sarcolemma membrane. Peroxidase-conjugated concanavalin A and wheat germ agglutinin lectins bind strongly to the isolated 120- and 100-kDa glycoproteins. Treatment with endoglycosidase F resulted in conversion of the 120-kDa glycoprotein to a form migrating at about 97 kDa. Treatment of the 100-kDa band with endoglycosidase F produced form of about 80 kDa. Endoglycosidase H digestion removes only 5% of the mass of both glycoproteins. the carbohydrate structure of both glycoproteins, is therefore, predicted to be at least 75% complex structure and 25% high mannose or hybrid structure. The 120- and 100-kDa glycoproteins are the major Ca2(+)-binding proteins in the sarcolemma membranes. Intact and endoglycosidase-treated glycoproteins bind 45Ca2+ as analyzed by a 45Ca2+ overlay technique. Using polyclonal antibodies, the 120- and 100-kDa glycoproteins were identified in muscle plasma membranes (ventricles, atria, and uterus smooth muscle). They were, however, not present in non-muscle tissues such as pancreas, liver, and kidney. The 120- and 100-kDa glycoproteins appear to be homologous molecules as judged by their similar V8 protease peptide maps, cross-reactivity with polyclonal antibody, and other physicochemical properties.

Canine gastric muscarinic receptors up-regulate after vagotomy

Postvagotomy (PV) gastroparesis is an infrequent but troublesome problem. To test the hypothesis that the rarity of the PV syndrome is due to compensatory up-regulation of muscarinic cholinergic receptors (mAChR), we measured changes in stomach mAChR and gastric acid secretion in dogs before and three weeks after truncal vagotomy. Maximum acid output dropped significantly one week PV and then partially recovered by three weeks PV. mAChR density changed in parallel and was significantly increased in body mucosa, body muscle, and antrum mucosa. In the body, changes in mAChR in mucosa correlated positively with changes in muscle, suggesting that mAChR binding in pinch biopsies of gastric mucosa might become useful in evaluating patients for postvagotomy syndrome. PV up-regulation of mAChR in the mucosa of the canine gastric body might explain PV recovery of gastric acid secretion.

Appearance of alpha-smooth muscle actin in human eye lens cells of anterior capsular cataract and in cultured bovine lens-forming cells

Using light and electron-microscopic immunolocalization techniques, and gel electrophoresis combined with immunoblotting, we have examined the expression of cytoskeletal proteins in normal human fetal, child and adult lenses, in human anterior capsular cataract and in bovine lens cells in vivo and in vitro. In this report, we focus our observations on the pattern of actin-isoform expression during normal and pathological situations in vivo and culture conditions. We have noted that cells of developing and mature human lenses as well as bovine lens cells in situ contain only beta- and gamma-actins. In contrast, alpha-smooth muscle (alpha-sm) actin, an isoform typical of smooth muscle differentiation, was demonstrated in bovine lens cells at different times of culture. Moreover, the multilayered cells observed in the subcapsular zone of human anterior capsular cataract were characterized by the presence of alpha-sm actin. Thus, extensive changes in actin-isoform expression take place in lens cells growing in culture and may also occur during cataractogenesis. The biological meaning of the appearance of a marker of myoid differentiation in the ectodermally derived lens-forming cells is discussed.

Distribution of estrogen and progesterone receptors and steroid-regulated gene products in the chick oviduct

The distribution of estrogen and progesterone receptors (ER and PR, respectively) was studied immunohistochemically in the chick oviduct. Estrogen receptor immunoreactivity was found only in the nuclei of glandular epithelial cells. Progesterone receptor was found in the nuclei of glandular and luminal epithelia, stroma, smooth muscle cells and in the mesothelium. The dissimilar distribution of ER and PR suggests that either ER concentration in the luminal epithelium and smooth muscle is very low (below the sensitivity of ER immunostaining) or that estrogens control their PR synthesis indirectly via ER in glandular cells. A known estrogen-inducible protein, ovalbumin, was localized in the same glandular epithelial cells as ER. A progestin-inducible protein, avidin, was found in part of the luminal and glandular epithelium cells but not in other PR-positive cell types. This indicates the importance of cellular differentiation in the regulation of avidin synthesis. Estrogen and progesterone administration had effects also on ER and PR immunoreactivity. Estrogen and progesterone administrations for 24 h decreased markedly the immunoreactivity of their receptors. The decrease in receptor immunoreactivity is most likely due to a transient loss of immunoreactive receptor protein, since the antibodies (H222, PR6) react both with transformed (4 S) and non-transformed (8 S) receptor forms. At the subcellular level, PR was localized in the chromatin by immunoelectron microscopy. Progestin administration seemed to decrease PR immunoreactivity especially in the heterochromatin area, suggesting that conformational chromatin rearrangements occur during down-regulation of PR.

M3-muscarinic receptor subtype predominates in the bovine iris sphincter smooth muscle and ciliary processes

The distribution of mRNAs encoding muscarinic acetylcholine receptor (mAChR) subtypes (M1, M2, M3, and M4) was investigated in the bovine iris-ciliary body by Northern blot hybridization with subtype-specific oligonucleotide probes that were complementary to unique regions of the M1, M2, M3, and M4 mAChRs. Whole rat brain RNA, which contains all four subtypes, was employed as a positive control. Both the iris sphincter and the ciliary processes were found to contain predominantly the M3 mAChR subtype and minor amounts of the M2 subtype. Traces of the M4 subtype were detected also in the ciliary processes.

Specific binding sites for prohormone atrial natriuretic peptides 1-30, 31-67 and 99-126

Two peptides with vasodilatory properties consisting of amino acids 1-30 and 31-67 of the 98 a.a. N-terminal end of the prohormone of atrial natriuretic factor (proANF) which circulates in man were investigated to determine if they have specific binding sites on membranes isolated from DDT1 MF-2 smooth muscle cells. Smooth muscle is a known biologic target of these peptides. Competitive binding experiments revealed that proANFs (1-30), (31-67), and (99-126) (i.e., C-terminus; ANF) each had specific and separate binding sites. The dissociation constants for proANFs (1-30), (31-67), and (99-126) binding were 0.11 nM, 4 nM, and 7.3 nM, respectively. The binding site concentrations for proANFs (1-30), (31-67), and ANF were 2.57, 59.91 and 40 fmols/10(6) cells, respectively. The number of binding sites per cell were 1548, 36,087, and 24,090, respectively, for proANFs (1-30), (31-67), and (99-126) (ANF). Each peptide bound to DDT1 MF-2 membranes between 10(-8) to 10(-11) M but could only bind to the other peptides' receptors at concentrations of 10(-6) and 10(-7)M. These results suggest that proANF(1-30) and proANF(31-67) do not work through the ANF receptor but rather have their own separate and distinct receptors that mediate their biologic effects.

Galanin binding sites in rat gastric and jejunal smooth muscle membrane preparations

Receptors for galanin in membranes from the rat gastric and jejunal smooth muscle were studied using [125I] radioiodinated synthetic porcine galanin. Specific binding was time and temperature dependent. At 32 degrees C radioligand was degraded in the presence of smooth muscle membranes in a time-dependent manner. At optimal experimental conditions, the equilibrium binding analyses showed the presence of a single population of high affinity binding sites in both the rat stomach and jejunum (Kd value of 2.77 +/- 0.78 nM and 4.93 +/- 1.74 nM for stomach and jejunal smooth muscle membranes, respectively). The concentration of the high affinity binding sites was 58.19 +/- 11.04 and 32.36 +/- 5.68 fmol/mg protein, for gastric and jejunal preparations, respectively. Specific binding was completely inhibited by 10(-6) M of nonradioactive galanin; was 75% blocked by 1 microM of galanin(9-29); it was 10% blocked by 1 microM of galanin(15-29). Galanin(1-15) at a concentration of 1 microM was ineffective for inhibiting [125I]galanin binding. Deletion of four C-terminal amino acid residues from galanin(9-29) to give galanin(9-25) also resulted in almost complete loss of affinity. Radioiodinated galanin and N-terminally deleted fragments had receptor binding potency in the following order: galanin(1-29) greater than galanin(9-29) greater than galanin(15-29). We conclude that the C-terminal part of the galanin chain is important for the rat gastric and jejunal smooth muscle membrane receptor recognition and binding and that N-terminal amino acid sequences are probably not so important, since galanin(1-15) was not active but galanin(9-29) retained most of the receptor binding activity.

Isolation and characterization of a novel molecular weight 11,000 Ca2(+)-binding protein from smooth muscle

A new low molecular weight calcium-binding protein, designated as SMCaBP-11, has been isolated from chicken gizzard using a phenyl-Sepharose affinity column followed by ion-exchange and gel filtration chromatographies. The isolated protein was homogeneous by the criteria of gel electrophoresis in the absence and presence of sodium dodecyl sulfate (NaDodSO4). Molecular weight studies by both sedimentation equilibrium in 6 M guanidine hydrochloride and 15% polyacrylamide-SDS gels indicated the subunit molecular weight to be 11,000, and since a molecular weight of 21,000 was obtained in native solvents, the protein exists as a dimer in benign medium. The amino acid composition of this protein is similar but distinct from other known low molecular weight Ca2(+)-binding proteins. Ca2(+)-binding assays using Arsenazo III (Sigma) indicated the protein to bind 2 mol of Ca2+/subunit. In non-SDS gels, the protein moved faster in the presence of EDTA, suggesting that Ca2+ binding affects its mobility in a manner similar to other smooth muscle calcium-binding proteins such as calmodulin and 67-kDa calcimedin. Upon binding calcium, the protein underwent a conformational change as revealed by UV difference spectroscopy and circular dichroism studies in the aromatic and far-ultraviolet range. When the protein was excited at 280 nm, the tyrosine fluorescence emission maximum was centered at 306 nm. Ca2+ addition resulted in a nearly 15% decrease in intrinsic fluorescence intensity. Fluorescence titration with Ca2+ exhibited two classes of calcium-binding sites with Kd values of 0.2 and 80 microM, in agreement with UV difference spectral data.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural and functional features of the alpha 3 chain indicate a bridging role for chicken collagen VI in connective tissues

Type VI collagen is a component of 100 nm long periodic filaments with a widespread distribution around collagen fibers and on the surface of cells. It is an unusual collagen constituted by three distinct chains, one of which (alpha 3) is much larger than the others and is encoded by a 9-kb mRNA. The amino acid sequence of the alpha 3(VI) deduced from the present cDNA clones specifies for a multidomain protein of at least 2648 residues made of a short collagenous sequence (336 residues), flanked at the N-terminus by nine 200 residue long repeating motifs and at the C-terminus by two similar motifs that share extensive identities with the collagen-binding type A repeats of von Willebrand factor. Type VI collagen and alpha 3(VI) fusion proteins bound to insolubilized type I collagen in a specific, time-dependent, and saturable manner. The alpha 3(VI) chain has three Arg-Gly-Asp sequences in the collagenous domain, and cell attachment was stimulated by the triple helix of type VI collagen and by alpha 3(VI) fusion proteins containing Arg-Gly-Asp sequences. This function was specifically inhibited by the Arg-Gly-Asp-Ser synthetic peptide. The type I collagen-binding and the cell-attachment properties of the alpha 3(VI) chain provide direct information for the role of type VI collagen in connective tissues.

Characterization of the major form of cholecystokinin in human intestine: CCK-58

Acid extracts of human intestines obtained from surgical samples or from organ donors contain cholecystokinin (CCK) immunoreactivity. From surgical samples, extracted and eluted quickly, greater than 75% of the CCK immunoreactivity eluted in the same region as purified canine CCK-58 during analytical reverse-phase high-pressure liquid chromatography (HPLC). A major portion of the CCK immunoreactivity from donor intestinal extracts also eluted in this region. This immunoreactivity has been purified from human intestinal extracts by a series of several reverse-phase and cation-exchange chromatographies. Amino acid and microsequence analysis showed that this immunoreactivity is human CCK-58. Tryptic digestion of purified human CCK-58 produced another immunoreactive form that eluted in the position of CCK-8 during analytical reverse-phase HPLC. The immunoreactivity of the trypsin-digested material was 2.6-fold higher than that of an identical sample of CCK-58 incubated without trypsin. Thus the carboxyl-terminal antibody used for radioimmunoassay cross-reacts greater than twofold less with human CCK-58. This diminished cross-reactivity would lead to an underestimation of the relative proportions of CCK-58 in tissue and plasma extracts. If CCK-58 is the major circulating form this diminished cross-reactivity would also lead to underestimations of the circulating levels of total CCK. Determination of human CCK-58 structure confirms that one of the major components of human CCK that expresses biological activity is CCK-58.

Expression of the VLA family of integrins in human intestine

The distribution of cells expressing the integrins VLA-1 to 6 in human intestine was examined by alkaline phosphatase immunohistochemistry using monoclonal antibodies specific for the individual alpha-chains of the VLA heterodimer. VLA-2,3, and 6 were expressed on all epithelial cells in the small and large bowel. VLA-1 was expressed on crypt cells in the small and large bowel, but was only weakly expressed or was absent on villus epithelial cells in the small bowel and colonic surface epithelial cells. All epithelia were negative for VLA-4 and VLA-5. Intraepithelial lymphocytes were VLA-1+ and VLA-4+. VLA-1,3, and 5 were expressed uniformly by muscularis propria, muscularis mucosae, pericrypt cells, and smooth muscle fibres within the villi. By contrast, VLA-2 and 4 were present only in pericrypt cells and fibres within the villi; they were absent from the muscularis mucosae. VLA-1,3,5, and 6 were expressed by endothelium. Staining of muscle fibres and endothelium in the lamina propria made it difficult to determine the extent of VLA expression on lamina propria lymphocytes. However, VLA-1+ cells with lymphoid morphology were only rarely seen. All mononuclear cells in the lamina propria were VLA-4+.

Antibacterial peptides from pig intestine: isolation of a mammalian cecropin

Pig small intestine was used as starting material for a batchwise isolation of a peptide fraction enriched in antibacterial activities against Escherichia coli (anti-Ec factor) and against Bacillus megaterium (anti-Bm factor). Separation and further purification were by different types of chromatography. Sequence analysis showed the anti-Bm factor to be apparently similar to vasoactive intestinal peptide. The anti-Ec factor was found to have a 31-residue sequence that was cecropin-like. It was named cecropin P1 and its structure was confirmed by solid-phase synthesis. Synthetic cecropin P1 with and without C-terminal amide was assayed on eight different bacteria. Mobility comparison between synthetic and natural cecropin P1 indicates that the natural peptide has a free C-terminal carboxyl group.

Kinetic evidence for insertion of actin monomers between the barbed ends of actin filaments and barbed end-bound insertin, a protein purified from smooth muscle

An actin polymerization-retarding protein was isolated from chicken gizzard smooth muscle. This protein copurified with vinculin on DEAE-cellulose and gel filtration columns. The polymerization-retarding protein could be separated from vinculin by hydroxylapatite chromatography. The isolated polymerization-retarding protein lost its activity within a few days, but was stable for weeks when it was not separated from vinculin. We termed the polymerization-retarding protein "insertin". Because of the instability of the isolated insertin, we investigated the effect of insertin-vinculin on actin polymerization. Insertin-vinculin retarded nucleated actin polymerization maximally fivefold. Polymerization at the pointed ends of gelsolin-capped actin filaments was not affected by insertin-vinculin, suggesting that insertin-vinculin binds to the barbed ends, but not to the pointed ends, of actin filaments. Retarded polymerization was observed even if the actin monomer concentration was between the critical concentrations of the ends of treadmilling actin filaments. As at this low monomer concentration the pointed ends depolymerize, monomers appeared to be inserted at the barbed ends between the terminal subunit and barbed end-bound insertin molecules. Insertin-vinculin was found not to increase the actin monomer concentration to the value of the pointed ends. These observations support the conclusion that insertin is not a barbed end-capping protein but an actin monomer-inserting protein. According to a quantitative analysis of the kinetic data, all observations could be explained by a model in which two insertin molecules were assumed to bind co-operatively to the barbed ends of actin filaments. Actin monomers were found to be inserted between the barbed ends and barbed end-bound insertin molecules at a rate of about 1 x 10(6) M-1 s-1. Insertin may be an essential part of the machinery of molecules that permit treadmilling of actin filaments in living cells by insertion of actin molecules between membranes and actin filaments.

Comparative growth dynamics and actin concentration between cultured human myofibroblasts from granulating wounds and dermal fibroblasts from normal skin

The normal contraction of open wounds and many forms of pathologic contracture are related by the presence of a contractile fibroblast known as a myofibroblast. The function of this cell has been postulated as a result of previous pharmacological, immunological, and biochemical testing on strips of contracted connective tissue. The purpose of this study was to develop a specific assay that could measure the concentration of one contractile element (actin) within cultured myofibroblasts isolated from a contracting wound and in normal fibroblasts from uninjured dermis. Rates of growth and actin concentration through 15 days of culture were compared among populations of paired control fibroblasts from normal dermis and granulating wound myofibroblasts from three patients. Growth curves showed that myofibroblasts always grew slower than fibroblasts. An enzyme-linked immunosorbent assay showed that actin concentration was generally greater in mass cultures of granulating wound myofibroblasts than in fibroblasts from uninjured dermis. During exponential growth (1-6 days) the average actin concentration among myofibroblast lines ranged from 24 to 62 pg/cell. Average actin levels among control fibroblasts ranged from 3 to 47 pg/cell during the same interval. After 15 days of culture, actin concentration peaked twice. The first actin peak occurred within the period of exponential growth. At confluency, cellular actin levels dropped. Superconfluent cultures exhibited a second actin peak that displayed an irregular pattern of actin concentration. The latter observation suggested an artifact that might be the result of three-dimensional matrix of cells that altered points of cell adhesion and produced an irregular pattern of actin concentration. These data show that the phenotype of increased actin in cultured myofibroblasts was carried over by myofibroblasts from contracted skin wounds to culture. Because of a higher concentration of actin in myofibroblasts than in undifferentiated fibroblasts, these data suggest that the differentiation process of myofibroblasts may be associated with an increased availability of monomeric actin for filament synthesis. This study demonstrates that the use of tissue culture and our enzyme-linked immunosorbent assay will be a useful method to study factors affecting myofibroblast phenotypic modulation. Future studies should be directed toward developing procedures for isolation of pure populations of myofibroblasts as well as extracellular matrices that would maintain the morphology of both differentiated myofibroblasts and normal undifferentiated fibroblasts.

Human salivary gland glycoconjugates: a lectin histochemical study

The glycoconjugate content of normal salivary glands has been extensively investigated in humans by biochemical means and in non-human mammals by histochemical methods. However, there have been few histochemical studies of human tissues. This paper describes the findings obtained in parotid, submandibular and minor salivary glands by applying a panel of 13 biotinylated lectins, directed against a range of N-linked, fucosylated and galactosylated sequences, using an avidin-peroxidase technique, with appropriate enzymatic and inhibitory sugar controls. The results were generally in accord with those observed in biochemical assays but the use of lectin histochemistry permitted the localization in situ of small amounts of oligosaccharide and, therefore, allowed the recognition of subtle tissue differences. This study expands the current knowledge on the glycoconjugate composition of salivary glands and their lectin histochemistry and serves as a baseline for further studies, particularly in the field of neoplasia.

Localization of vimentin in myoepithelial cells of the rat mammary gland

Myoepithelial cells in the virgin rat mammary gland have been shown to contain vimentin, using a polyclonal antiserum to vimentin purified from hamster fibroblasts. This antiserum has been shown to be specific for vimentin by immunoblotting and ELISA techniques. Similar results were obtained with a monoclonal antibody to vimentin. In the mammary glands of pregnant rats, the staining with vimentin antibodies is much weaker in the myoepithelial cells of the developing alveolar buds than in the main ducts. Similarly, in lactating glands, the staining of myoepithelial cells is much weaker in the secretory alveoli than in lactiferous sinuses. In each case, staining with antivimentin co-localizes with staining with polyclonal antisera to callous keratin (which specifically stain myoepithelial cells in the rat mammary gland).

Differential expression of smooth muscle alpha-like actin between benign and malignant human pigment tissues

When examining proteins in human pigment tissues, we found that a third actin-like protein, in addition to beta- and gamma-actin was more frequent and in a larger amount in benign tissues such as blue nevus and nevus pigmentosus, than in malignant melanoma. This third actin-like protein was immunologically stained with monoclonal antibodies reacting with several actin species and specific for smooth muscle alpha-actin. We propose that this third actin-like protein is probably smooth muscle alpha-actin and that different expressions of this third actin may possibly serve as a sensitive biochemical marker for the diagnosis of human malignant melanoma.

[Tissue concentrations of beta-methyl-digoxin in children]

Beta-methyl-digoxin concentrations in adipose, skeletal muscle and myocardial tissues, were studied in 8 patients undergoing by-pass surgery because of congenital heart disease. Correlation between doses/kg, plasmatic and tissue concentrations were analysed. We found statistically correlation between doses/kg and plasmatic concentrations; doses/kg and skeletal muscle concentrations (p less than 0.01); plasmatic and skeletal muscle concentrations (p less than 0.05). Concentrations was significantly greater in myocardial than adipose tissue before extracorporeal circulation (p less than 0.01); and significantly greater than adipose (p less than 0.01) and skeletal muscle (p less than 0.05) tissues after extracorporeal circulation. Extracorporeal circulation lessens adipose and skeletal muscle concentrations, but increases myocardial concentrations significantly (p less than 0.05). It is concluded, that the behaviour of beta-methyl-digoxin, in relation with tissue concentrations, is similar to digoxin.

Tissue specific distribution of calcyclin--10.5 kDa Ca2+-binding protein

Expression of calcyclin in different cell lines and mouse tissues was determined with polyclonal antibodies raised against calcyclin from Ehrlich ascites tumour (EAT) cells. The protein was detected in mouse skeletal and cardiac muscle, in lung, kidney and spleen, and was especially enriched in mouse smooth muscle as well as in rat fibroblasts. No positive immunological reaction was detected in mouse brain, liver and intestine and some tumourigenic cell lines. The level of calcyclin mRNA found in different cells and tissues corresponded well to the calcyclin level estimated by immunoblotting. The calcyclin-like protein was purified from mouse stomach and appeared to be very similar to the EAT protein.

Identification in turkey gizzard of an acidic protein related to the C-terminal portion of smooth muscle myosin light chain kinase

The isolation of an acidic protein, pI 4.5, that is abundant in turkey gizzard is described. Its apparent molecular weight measured by electrophoretic procedures is 24,000. This protein is phosphorylated by the catalytic subunit of the cAMP-dependent protein kinase and one phosphorylation site is indicated. From sequence determinations of tryptic peptides it is concluded that this protein is closely related to the C-terminal part of smooth muscle myosin light chain kinase. The initiation site for the protein is to the C-terminal side of the calmodulin-binding site. From the sequence data an estimated molecular weight is 18,000. This protein is expressed independently, as indicated by a blocked N terminus, and is probably the translation product of the 2.7-kilobase RNA detected previously in chicken gizzard (Guerriero, V., Jr., Russo, M. A., Olson, N. J., Putkey, J. A., and Means, A. R. (1986) Biochemistry 25, 8372-8381). Because of its putative origin as the C-terminal end of smooth muscle myosin light chain kinase, it is termed "telokin" (from a combination of kinase and the Greek telos, "end").

Two isoforms of smooth muscle myosin regulatory light chain in chicken gizzard

We isolated a cDNA clone for a new isoform of chicken smooth muscle myosin regulatory light chain (MRLC) from a cDNA library of embryonic chicken gizzard. The deduced amino acid sequence was different in 10 amino acid residues from the previously reported polypeptide sequences of chicken gizzard MRLC. The in vitro transcription/translation product from the cDNA comigrated with a minor isoform of chicken gizzard MRLC (L20-B) in a two-dimensional gel electrophoresis. This isoform was detected only in the embryonic gizzard and was slightly more acidic than the predominant isoform (L20-A). The partial polypeptide sequence of L20-A was confirmed to be identical to the previously reported MRLC sequence. Nevertheless, Northern blot analysis showed that L20-B-related mRNAs were present in both the embryonic and adult gizzard. Non-denaturing pyrophosphate polyacrylamide gel electrophoresis showed that the in vitro transcription/translation product could be associated with native myosin when mixed and coprecipitated in a low-ionic-strength buffer with adult chicken gizzard myosin. Moreover, the coprecipitated translation product was phosphorylated in vitro by chicken gizzard myosin light chain kinase apparently more rapidly than L20-A on the native myosin heavy chain. From these findings, we concluded that at least two isoforms of smooth muscle MRLC exist in chicken gizzard and that their expression may be regulated translationally depending on the developmental stage.

Multiple types of voltage-dependent Ca channels in mammalian intestinal smooth muscle cells

(1) Whole-cell and single channel recording techniques have been applied to smooth muscle cells isolated from guinea-pig taenia coli to examine whether multiple types of Ca channels exist. (2) Whole-cell recordings under physiological Ca concentration (1.8 mM) revealed two current components with fast and slow inactivating kinetics. The fast inactivating component was present when cells were held at very negative potentials (-80 mV). It was insensitive to the dihydropyridine (DHP) derivative, nifedipine. In contrast, the slow inactivating component was present at less negative holding potentials. It was blocked by nifedipine. (3) The two current components were found to have closely similar voltage dependencies for activation. (4) These results suggest that the fast inactivating decay of the Ca current was mediated not only by the entry of Ca into the cell but also by a voltage-dependent process via a different type of Ca channel with fast inactivating kinetics. (5) Recordings from cell-attached membrane patches with 100 mM external Ba clearly showed the existence of multiple types of Ca channels with different conductances. (6) The large conductance channels (30 pS) activated at more positive potentials (0 mV) and their averaged current decayed much more slowly. The DHP Ca antagonist, nifedipine, inhibited the large conductance channels increasing the proportion of blank sweeps and reducing the averaged current. On the other hand, the DHP Ca-agonist, BayK 8644, increased the average current by increasing the mean open-times of the large conductance channels. The presence of micromolar Cd in the patch pipettes produced a flickering block of the large conductance channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Caldesmon150, caldesmon77 and skeletal muscle troponin T share a common antigenic determinant

Caldesmon and troponin are known to control actin-myosin interaction in smooth and striated muscle. We showed that polyclonal antibodies to smooth muscle caldesmon150 cross-react with non-muscle caldesmon77 and with skeletal muscle troponin T. The epitope recognized by caldesmon antibodies is located in the CB 2 peptide [residues 71-151] of troponin T. It is supposed that the observed cross-reactivity is due to the common structure of the tropomyosin-binding site of caldesmon and troponin T.

[Analysis of the glucocorticoid receptor of bovine tracheal smooth muscle]

Though the therapeutic efficacy of glucocorticoids on bronchial asthma has been attributed mainly to their anti-allergic and anti-inflammatory effects, the possibility of intervention of glucocorticoids in bronchial asthma might be an important parallel process. However, little is known about the mechanism of glucocorticoid action on tracheal muscle and there is insufficient basic information about the glucocorticoid receptor of tracheal muscle. Accordingly we set out to analyze the glucocorticoid receptor of bovine tracheal muscle. Bovine tracheal muscle was used because it is plentiful enough for biochemical analysis. Our results showed that a small amount (0.08 pmol/mg.protein) of glucocorticoid binder of high affinity (kd = 4.6 nM) was present in the cytosol of bovine bronchial muscle. The binder did not show any affinity for estradiol, dihydrotestosterone or andronsterone, but showed a low affinity for progesterone. Furthermore, the binder underwent salt-dependent variation of its molecular form (9.2S under low salt condition and 4.6S under high salt condition) typical of steroid receptors. These results indicated the presence of a glucocorticoid receptor in the tracheal muscle, suggesting that glucocorticoid acts on bronchial muscle in therapeutic practice on bronchial asthma.

Transepithelial prostacyclin gradient in isolated canine trachea

Cyclooxygenase products of arachidonic acid, potential modulators of airway smooth muscle, have recently been described in bronchoalveolar lavage from canine lungs. To evaluate the possibility that airway epithelium represents a barrier to movement of prostacyclin (PGI2), an important bronchodilator synthesized by isolated airway, we measured the concentrations of 6-oxoprostaglandin F1 alpha (6-oxo-PGF1 alpha), the stable degradation product of PGI2, on the mucosal and serosal sides of isolated canine tracheal segments (CTS) mounted in Ussing chambers. 6-oxo-PGF1 alpha was measured by radioimmunoassay after purification by high-performance liquid chromatography. The concentration of 6-oxo-PGF1 alpha was significantly higher on the serosal than the mucosal side of CTS (1,262 +/- 252 vs. 390 +/- 168 pg.min-1.g-1, n = 8, P less than 0.05). A significant correlation was present between 6-oxo-PGF1 alpha measured on both sides of each CTS (r = 0.778, n = 26, P less than 0.01). 6-oxo-PGF1 alpha production from CTS stripped of mucosa was significantly greater than from isolated mucosa. Radiochromatograms obtained after incubation with [3H]arachidonic acid and calcium ionophore A23187 confirmed PGI2 as the predominant cyclooxygenase product of the submucosa, whereas the mucosa produced only small amounts of PGI2 in proportion to other cyclooxygenase products. PGI2 (10(-8) to 10(-6) M) applied to the mucosal surface of closed tracheal segments precontracted with histamine resulted in no significant relaxation, whereas serosal application showed a concentration-dependent effect. Radiolabeled 6-oxo-PGF1 alpha did not cross the isolated epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Pig brain homogenates contain smooth muscle myosin and cytoplasmic myosin isoforms

Three myosin isoforms, two of smooth muscle and one of cytoplasmic origin, were found in porcine brain by Western blotting analysis with antibodies specific for smooth and cytoplasmic myosins. The smooth muscle isoforms comprise at least 30% of the total myosin present. Brain tissue is therefore not a suitable source for the isolation of pure cytoplasmic contractile proteins.

35 kDa proteins are not components of vertebrate smooth muscle thin filaments

A 35 kDa protein present in vertebrate smooth muscle and capable of binding to purified actin does not appear to be a constituent of smooth-muscle thin filaments in vivo; instead, it is more likely to be a component easily solubilized from particulate material which then spuriously interacts with actin.

The distribution of heavy-chain isoforms of myosin in airways smooth muscle from adult and neonate humans

Changes in the expression of heavy chains of myosin during development determine the functional characteristics of striated muscles. The distribution of heavy-chain isoforms of smooth-muscle myosin was determined in the airways of adult and infant humans to see whether it might underlie the hyperreactivity of human airways. The protein bands corresponding to myosin were separated using SDS/polyacrylamide-gel electrophoresis (4% gels) and identified by immunoblotting using both monoclonal and polyclonal antibodies against smooth-muscle myosin and non-muscle myosin. The relative proportion of each heavy chain stained by Coomassie Blue was measured by densitometric scanning. Three major bands corresponding to myosin heavy-chain isoforms were found; the two slower migrating bands (MHC1 and MHC2) were smooth-muscle myosin, and the third band was non-muscle myosin. The MHC1/MHC2 ratio was 0.69:1 in adult bronchus, and in infant bronchus and trachea. This contrasted with the airway smooth muscle in pigs, which was run concurrently, where the smooth-muscle heavy-chain ratio changed with development [Mohammad & Sparrow (1988) FEBS Lett. 228, 109-112]. The non-muscle myosin heavy chain comprised 63% of the smooth-muscle myosin. In both adult and infant lungs an additional putative myosin heavy chain which migrated slightly more rapidly than non-muscle myosin heavy chain was identified using the monoclonal smooth-muscle myosin antibody BF 48. This was unique to the human species.

Molecular and cellular analysis of histamine H1 receptors on cultured smooth muscle cells

Histamine is an important mediator of immediate hypersensitivity for both animals and humans. The action of histamine on target tissues is believed to be mediated by specific cell surface receptors, especially H1 and H2 receptors for hypersensitivity and inflammatory reactions, which involve stimulation of smooth muscle contractility, alterations in vascular permeability, and modifications in the activities of macrophages and lymphocytes. Although the nature of histamine receptors in the brain and peripheral tissues has been studied extensively by many laboratories, the molecular mechanism of histamine receptor-mediated reactions is not fully understood, mainly because histamine receptors are incompletely characterized from the biochemical point of view. In previous studies, we have found that the cultured smooth muscle cell line DDT1MF-2, derived from hamster vas deferens, expresses low-affinity histamine H1 receptors and responds biochemically and functionally to H1-specific stimulation (Mitsuhashi and Payan, J Cell Physiol 134:367, 1988). This cell line provides a model for analyzing the biochemical responses of H1 receptor-mediated reactions in peripheral tissues. In this review, we summarized our recent progress in the study of low-affinity H1 receptors on DDT1MF-2 cells.

Non-adrenergic non-cholinergic nervous control of airways

Traditionally, the tone of bronchial smooth muscle is mediated through the balance of two autonomic nervous systems. The existence of a third non-adrenergic non-cholinergic (NANC) nervous system in the lung has been demonstrated in animals. In contrast to high density parasympathetic innervation of smooth muscle, no evidence of adrenergic nerves was found in human airways. Electrical field stimulation of tracheal strips in guinea-pig produced an initial contraction followed by a relaxation. The contraction was blocked by atropine but the relaxation was not inhibited by a beta-adrenergic blocking agent. Immunohistochemical studies have shown that vasoactive intestinal peptide (VIP)-like immunoreactive nerves are present in the central nervous system and in the peripheral neuronal system of mammals including the human respiratory tract. Autoradiographic and immunocytochemical studies have demonstrated a high density of VIP receptors in airway epithelium, submucosal glands, pulmonary vessels and smooth muscle, especially in large airways. Functional studies in humans have confirmed the regulating role of VIP principally in the large airway.

Tissue-specific expression of profilin

Expression of profilin and profilin:actin ratios in vertebrates were determined with polyclonal antibodies against profilin and actin. Profilin was detected in a wide variety of bovine tissues and was enriched in smooth muscle of bovine, porcine and avian origin. The protein was purified from pig stomach muscle tissue. Smooth muscle profilin was found to be more effective in inhibiting the polymerization of skeletal muscle actin than thymus profilin purified by the same method.

A simple enzymic method to separate [3H]inositol 1,4,5- and 1,3,4-trisphosphate isomers in tissue extracts

A novel method to separate [3H]Ins(1,4,5)P3 and [3H]Ins(1,3,4)P3 in tissue extracts is described. It is based on the selective metabolism of Ins(1,3,4)P3 by a crude cerebral supernatant in a Mg2+-free buffer followed by separation of [3H]inositol trisphosphates using conventional anion-exchange chromatography. Evaluation of the assay was performed using [3H]Ins(1,3,4)P3 standards and tissue extracts containing different proportions of [3H]Ins(1,4,5)P3 and [3H]Ins(1,3,4)P3. Parallel h.p.l.c. separations of extracts established the selective and complete metabolism of [3H]Ins(1,3,4)P3 under the above conditions and demonstrated that the enzymic method provides an accurate estimate of the trisphosphate isomers in rat cerebral cortex, parotid gland and bovine tracheal smooth muscle.

Alpha-smooth muscle actin in parenchymal cells of bleomycin-injured rat lung

Bleomycin causes focally diffuse interstitial fibrosis characterized by increases in the number and volume of contractile filament-laden parenchymal cells, as well as increased parenchymal contractility. However, the origin of these cells and their relationship to altered contractility, remain unknown. We now have used immunohistochemical methods to ask if cells containing smooth muscle actin and myosin are present in involved regions of parenchyma. Staining of the parenchyma of control lungs with a monoclonal antibody against alpha-smooth muscle actin is sparse, consisting of reactivity with the alveolar entrance ring (septal tip) cells as well as occasional reactivity of alveolar wall cells that may represent pericytes or contractile interstitial cells. Increased alpha-smooth muscle actin staining was observed in areas of parenchymal damage in lungs from animals sacrificed between 1 and 4 weeks postbleomycin instillation. This reactivity included altered staining of the airway and vessel smooth muscle coat as well as thickened septal tips. In addition, newly reactive cells were observed in interstitial and intraalveolar regions and in bands of thickened submesothelial tissue. Staining was most intense in the focal fibrotic lesions which are characteristic of this injury. By contrast, parenchymal reactivity with a polyclonal antibody against smooth muscle myosin at the later time points shows only a mild increase in punctate staining in the damaged foci. We hypothesize that the substantial increase in alpha-smooth muscle actin containing cells in fibrotic regions of involved parenchyma after bleomycin injury is responsible for the altered morphologic, biochemical, and mechanical properties that we have observed.

A Ca2(+)-sensitive glycoprotein, GP90, associated with the cytoskeleton from brain and gizzard

We describe here the expression during development, tissue distribution and molecular properties of GP90: a major concanavalin A (ConA)-binding glycoprotein present in the neuronal membrane skeleton from chicken brain. GP90 is co-isolated with, and has a similar developmental profile to contactin (previously called GP130). In whole brain, GP90 undergoes rapid synthesis between embryonic days 10 and 12. Unlike contactin, it is not restricted to nervous tissue and is quite abundant in gizzard, where there are two antigenically related proteins of 100K and 90K (K = 10(3) Mr). In both brain and gizzard GP90 and (GP100) are enriched in the membrane skeleton fraction. Trypsinization of live cells suggest that GP90 from gizzard is related to GP100 by the removal of a polypeptide chain. GP90 from both neurones and gizzard cells is protected from proteolysis by the presence of extracellular Ca2+. In the absence of Ca2+ a soluble fragment of approximately 70K can be released from the surface of cells indicating that a large fraction of GP90 is extracellular. Deglycosylation of GP90 from brain using endoglycosidase F demonstrates the presence of at least five carbohydrate chains and a polypeptide chain of approximately 80K. Immunofluorescence studies show that GP90 is exposed on the surface of cultured neurones, gizzard cells and most glial cells with the exception of Schwann cells. It is observed in clusters or patches even when cells are prefixed, suggesting this may be the normal distribution of GP90.

Substance P and gastrin releasing peptide in bovine mesenteric lymphatic vessels: chemical characterization and action

Alcoholic extracts of bovine mesenteric lymphatic vessels were assayed for the presence of SP, GRP, VIP, PHI, GIP and NT using specific radioimmunoassays. SP and GRP immunoreactivities were detected at concentrations of 190 +/- 20 and 1,000 +/- 130 pg.g-1, respectively. No significant levels of immunoreactivity were detected for any of the other peptides. SP and GRP immunoreactivities coeluted with their synthetic counterparts from both Sephadex G-50 and reversed phase HPLC columns. Synthetic SP (10(-9)-10(-7) M) and the naturally occurring analogue of GRP, bombesin (10(-9)-10(-7) M), increased spontaneous contraction rate in isolated vessel segments. This excitatory effect was not blocked by the alpha-adrenoceptor antagonist phentolamine (3 x 10(-6) M).

Gestational changes in calbindin-D9k in rat uterus, yolk sac, and placenta: implications for maternal-fetal calcium transport and uterine muscle function

Calbindin-D9k was quantified and its cellular location was defined in uterus, yolk sac, and placenta. In late gestation (days 17 to term) coordinated induction of calbindin-D9k was seen in uterine epithelial lining cells and juxtaposed yolk sac visceral epithelium as well as the intraplacental yolk sac epithelium. The induction of calbindin-D9k in these cells coincided with the time of exponential fetal bone growth and maximal fetal accumulation of calcium, suggesting a role of the protein in these epithelial layers in maternal-fetal calcium transport. Dynamic changes also occurred in the calbindin-D9k contents of the two layers of uterine smooth muscle (outer longitudinal and inner circular) during mid- and late gestation. During early pregnancy (days 0-4), calbindin-D9k was present in the two smooth muscle layers. By midgestation (day 10), calbindin-D9k had decreased by a factor of 10 in these tissue layers. During late gestation calbindin-D9k rebounded in the inner circular smooth muscle layer. These uterine changes of early and midgestation were reproduced by the endocrine changes of pseudopregnancy. Progesterone appeared to be a good candidate for controlling the midgestational decrease of uterine muscle calbindin-D9k, as it blunted estrogen's induction of the protein in the muscle layers and stroma in a dose-dependent manner. Changes in myometrial calbindin-D9k may reflect variations in muscular calcium storage, thereby representing alterations in potential for contraction.

Caldesmon: anomalous electrophoretic behaviour in polyacrylamide gel

In SDS gels caldesmon (Mr = 140 kDa) and myosin light chain kinase (Mr = 130 kDa) migrate as a closely separated doublet. When glycerol is added to the gel caldesmon is characterized by an anomalous migration. In fact under this latter condition, the distance between caldesmon and myosin light chain kinase is enhanced by two-three times. The nature of putative caldesmon and myosin light chain kinase was confirmed by physicochemical, enzymatic and immunological methods.

Regulation of calcium concentration in voltage-clamped smooth muscle cells

The regulation of intracellular calcium concentration in single smooth muscle cells was investigated by simultaneously monitoring electrical events at the surface membrane and calcium concentration in the cytosol. Cytosolic calcium concentration rose rapidly during an action potential or during a voltage-clamp pulse that elicited calcium current; a train of voltage-clamp pulses caused further increases in the calcium concentration up to a limit of approximately 1 microM. The decline of the calcium concentration back to resting levels occurred at rates that varied with the calcium concentration in an apparently saturable manner. Moreover, the rate of decline at any given calcium concentration was enhanced after a higher, more prolonged increase of calcium. The process responsible for this enhancement persisted for many seconds after the calcium concentration returned to resting levels. Thus, the magnitude and duration of a calcium transient appear to regulate the subsequent calcium removal.

Caldesmon, acidic amino acids and molecular weight determinations

Recent estimates of molecular weight and cDNA sequencing indicate that smooth muscle caldesmons are considerably smaller than previously thought. The anomalous behaviour of these proteins during SDS-polyacrylamide gel electrophoresis can be correlated with their high acidic amino acid content. The results suggest a need to re-evaluate the stoichiometric relations of caldesmon to tropomyosin and actin in thin filaments and its presumed 1:1 interaction with calmodulin.

Caldesmon and the structure of smooth muscle thin filaments: immunolocalization of caldesmon on thin filaments

Antibodies reacting with chicken gizzard caldesmon were used to determine the distribution of caldesmon on smooth muscle thin filaments. Antibodies developed against both the intact caldesmon molecule and a 40 kilodalton proteolytic fragment cause thin filaments to aggregate laterally. Aggregates produced with the latter antibody display regular periodic labelling with a repeat of approximately 38 nm, a distribution characteristic of proteins associated with tropomyosin on thin filaments. The stoichiometry of caldesmon on thin filaments has been critically reevaluated and alternative models of caldesmon distribution on thin filaments are proposed.

Functional and biochemical characterization of the human gallbladder muscularis cholecystokinin receptor

Gallbladders removed at cholecystectomy are a potentially useful source of human receptor for the gastrointestinal peptide hormone cholecystokinin (CCK). Seven healthy gallbladders (removed incidentally at time of resection of hepatic metastases) and 50 diseased gallbladders were studied. Cholecystokinin radioligand binding to an enriched plasma membrane preparation from these tissues was shown to be rapid, reversible, temperature-dependent, saturable, specific, and high-affinity. Computer analysis of equilibrium binding data using the Ligand program best fit a single class of binding sites with Kd = 1.0 +/- 0.1 nM (mean +/- SEM). This was similar in health and disease, with no apparent differences related to age, gender, or body habitus. The structural specificity for binding to this site correlated well with relative potencies for CCK-gastrin peptides to stimulate gallbladder contraction. To biochemically characterize this receptor, we used a battery of reagents, including "long" (125I-Bolton Hunter-CCK-33) and "short" 125I-D-Try-Gly-[(Nle28,31)CCK-26-33] probes that were cross-linkable through their amino terminus and a monofunctional probe with a photolabile group at its carboxyl terminus 125I-D-Tyr-Gly[(Nle28,31,pNO2-Phe33)CCK-26-33]. All probes specifically labeled a human gallbladder muscularis protein of Mr = 85,000-95,000, which was also independent of diagnosis. Labeling of this band was inhibited in a concentration-dependent manner by CCK-8 and by L-364,718. Thus, the CCK receptor present on the very common surgically removed human gallbladder is functionally and biochemically intact and is useful for further characterization.