[Inhibitory effect and mechanism of scopolamine on respiration]

In conscious rabbits, dogs and anaesthetized dogs, the respiratory frequency (FR), tidal volume (Vt) and minute ventilation (Vm) were determined in order to confirm whether the respiratory effect of scopolamine is stimulatory or inhibitory. Arterial blood samples were taken intermittently and analyzed for Po2, Pco2 and pH. When scopolamine was injected i.c.v., i.a. and i.v., the decrease of FR, Vt, Vm and Po2 and the increase of Pco2 were observed in two animals. When the drug was given in clinical doses used for treating respiratory failure, the effect was seen still observable. The results indicate that scopolamine inhibits respiration. Moreover, it was observed that excitatory effect of pilocarpine on respiration can be antagonized by scopolamine, but the inhibitory effect of 6 beta-acetoxy nortropane can not be antagonized, on the contrary, can be coordinated. The above results suggest that respiratory inhibition induced by scopolamine may be related to blocking M1-R of the respiratory center.

Organization and fine structure of a pacemaker derived from fetal rat myocardium

At an unknown point in mammalian development, cardiac precursor cells become committed to the cardiocyte phenotype. Certain of these are believed to specialize further into pacemaker cardiocytes. By culturing explanted embryonic ventricles into in vivo organ culture (Tucker DC, Snider C, Woods WT Jr: Pediatr Res 23:637-642, 1988), we observed pacemaker cells arising apparently from cardiocytes. We hypothesized that this event can be triggered by intercellular attachments, innervation, vascularization, or other factors. The present study was designed to test the hypothesis that primitive ventricular cells in the tubular heart can organize into an anatomically and electrophysiologically distinct pacemaker structure in the absence of innervation or vascularization from extrinsic sources. Developing ventricles of tubular hearts from 10-d-old rat embryos (n = 22) were excised and incubated in culture dishes. Within each explant, a group of cells organized into a uniform cluster (diameter, 150 +/- 50 microns) after 8 +/- 2 d in culture. These cells resembled immature conduction system cells and had electrophysiologic features similar to those of mature pacemaker cells. Single-cell action potentials and impulse conduction patterns proved that the pacemaker cluster was the dominant pacemaker for the entire explant. These results confirm that, in the absence of extrinsic nerves and blood vessels, culture of the tubular ventricle elicits formation of an organized pacemaker, resembling the mature cardiac pacemaker and suggesting that contact with the culture dish surface or some other factor triggers conversion of cardiocytes to the pacemaker phenotype.

Overexpression of protein kinase C-zeta stimulates leukemic cell differentiation

A function for protein kinase C-zeta (PKC-zeta), a member of the phorbol ester nonresponsive atypical protein kinase C subfamily, in modulating differentiation was examined in the leukemic U937 cell. Transfected U937 cells stably overexpressing PKC-zeta displayed a longer doubling time, lower saturation density at confluency, and an increase in adherence to plastic as compared to control cells. PKC-zeta cells expressed a more differentiated phenotype as assessed by changes in morphology, surface antigen expression, and lysosomal enzyme activities and were distinct from parental U937 cells stimulated to differentiate by exposure to phorbol esters. In contrast to parental U937 cells, PKC-zeta cells constitutively expressed mRNA transcripts for c-jun and a low mobility AP-1 binding activity. Thus, PKC-zeta overexpression stimulates a type of phenotypic differentiation that differs significantly from maturation occurring upon activation of other PKC subfamilies induced by phorbol ester treatment. Increased expression of the c-jun protooncogene and an increase in AP-1 binding activity in PKC-zeta cells provides a potential mechanism for explaining the altered differentiation status of this cell.

Effects of chronic phorbol ester treatment on protein kinase C activity, content, and gene expression in the human monoblastoid U937 cell

Immediate and sustained signal transduction is involved in mediating phorbol ester-induced changes in growth and differentiation. Activation of protein kinase C (PKC) is the initial step in phorbol ester-induced signal transduction. By virtue of preferential down-regulation of individual isoforms and generation of proteolytically derived kinase activities, the signal transduced by sustained activation of this pathway may differ substantially from that generated initially upon application of the phorbol ester. To examine the effect of chronic phorbol ester-induced activation of this pathway, the relationship between PKC activity/content and AP-1 binding activity and gene expression was studied in the U937 cell. Phorbol ester-induced differentiation of the U937 cell into a monocyte/macrophage-like cell requires sustained activation of the PKC pathway. AP-1 binding activity was enhanced by 12-O-tetradecanoylphorbol-13-acetate (TPA) and in a temporally dependent manner, with conversion of a high to low mobility band shift occurring after a 12-h exposure to TPA. After a 72-h exposure, AP-1 binding activity was maximally increased by 1 nM TPA and remained elevated to a similar degree even after treatment with 600 nM TPA. Enhanced AP-1 binding activity was dependent upon continuous exposure to TPA and was not secondary to differentiation. A 72-h treatment with one nM TPA maximally increased expression of c-jun, krox-24, and jun-B mRNA transcripts. Exposure to higher TPA concentrations decreased the content of these transcripts. Maximal expression of collagenase and plasminogen activator receptor transcripts required exposure to much higher TPA concentrations (100 nM).(ABSTRACT TRUNCATED AT 250 WORDS)

Dominant and nondominant negative C-erbA beta 1 receptors associated with thyroid hormone resistance syndromes augment 12-O-tetradecanoyl-phorbol-13-acetate induction of the collagenase promoter and exhibit defective 3,5,3'-triiodothyronine-mediated repression

C-erbA receptors and v-erbA have been shown to functionally interact with 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-inducible gene expression. These proteins enhance trans-activation by c-jun, and the c-erbA receptors in the presence of thyroid hormone repress TPA and c-jun induction of transcription. Also, v-erbA can abrogate T3-mediated repression. We have examined how dominant negative (S and CL) and nondominant negative (G-H) receptors cloned from various patients with thyroid hormone resistance syndromes affect expression of the collagenase promoter induced with TPA. The CL receptor (ARG315HIS mutation) has a 2-fold reduction in T3-binding affinity compared with human c-erbA beta 1 wild-type (WT) receptor, whereas the G-H receptor (ARG311HIS) and S receptor (deletion, THR codon 332) have T3-binding affinities reduced by 100-fold and greater than 100-fold, respectively. These mutant receptors were cotransfected with a collagenase promoter (-1200 to +63 base pairs) chloramphenicol acetyltransferase reporter gene (Col-CAT) into COS-7 cells. Levels of CAT reporter gene expression after transient transfection were determined in the presence or absence of 3-10 nM T3 and the presence or absence of 100 nM TPA. Unoccupied CL receptor and G-H and S receptors stimulated TPA-induced Col-CAT expression 1.5- to 9-fold. The CL receptor with thyroid hormone totally repressed TPA induction of the collagenase receptor. In the presence of thyroid hormone, the enhancing effects by S and G-H receptors on TPA-induced Col-CAT expression were unaffected and minimally diminished, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The reaction of bovine lens alpha A-crystallin with aspirin

Acetylation of the lysines of bovine lens alpha A-crystallin has been examined after 0-48-hr incubations of whole alpha-crystallins in 100 mM aspirin. The alpha A-crystallins were isolated after the incubation, proteolytically digested into peptides which were separated by reversed phase HPLC and analysed by mass spectrometry. For the reaction conditions used in this investigation, acetylated lysyl residues were the principal products. The extent of acetylation was quantified from the intensities of the peaks in the fast atom bombardment mass spectra of the modified and unmodified peptides. The modified lysine containing peptides demonstrated that all seven lysyl residues of alpha A-crystallin reacted with aspirin; the extent of acetylation at each lysyl residue varied. Plots of the extent of acetylation vs. time were used to calculate rate constants for the reaction at each lysyl residue. The rate constant for the acetylation of Lys 166, the most reactive, was about seven times greater than for Lys 88, the least reactive. These rate constants were used to calculate the yield of predicted products for the reaction of alpha-crystallin with therapeutic concentrations of aspirin. Comparison of the yield of acetylated alpha-crystallin with the yield of carbamylated alpha-crystallin that might occur due to renal failure indicates that aspirin is not likely to be an effective inhibitor of cataract due to carbamylation of lysyl residues.

Reaction of aspirin with cysteinyl residues of lens gamma-crystallins: a mechanism for the proposed anti-cataract effect of aspirin

Incubation of lens crystallins with aspirin inhibits the development of opacities caused by cyanate. Cyanate-induced opacities are thought to be due to carbamylation of the lysyl residues which causes a decrease in the protein charge and subsequent conformational changes that permit disulfide bonding. Because aspirin can also react with lysyl residues, it has been proposed that the aspirin inhibition of cataractogenesis is due to acetylation of the lysyl residues which would block their reaction with cyanate. However, acetylation of lysyl residues also lowers the protein charge and would be expected to effect changes in protein conformation similar to those caused by carbamylation. Therefore, acetylation of the lysyl residues is not a satisfactory explanation for the inhibitory effect of aspirin on lens opacification. Our investigations of the reactions of cyanate and aspirin with bovine gamma II-crystallins show that the cysteinyl residues are also carbamylated and acetylated at pH 7.4. At this pH, the carbamylation at the cysteinyl residues is reversible, leading to regeneration of the thiol group and disulfide bonding. In contrast, the acetylation at cysteinyl residues is stable at pH 7.4 and can prevent disulfide bonding. This difference in stability explains how cyanate promotes, and aspirin inhibits, cataractogenesis.

Rates of carbamylation of specific lysyl residues in bovine alpha-crystallins

Previous investigations indicate that some forms of cataract may be due to the reactions of isocyanate with lens proteins. The present investigation was directed toward identifying the products of these reactions and determining rate constants for their formation. Bovine alpha-crystallins were incubated with isocyanate and separated into alpha A- and alpha B-crystallins by reversed-phase HPLC (high-performance liquid chromatography). Products of the reaction of isocyanate with alpha-crystallins were analyzed by mass spectrometry and isoelectric focusing. Proteolytic digests of carbamylated alpha A were analyzed by HPLC and fast atom bombardment mass spectrometry to determine the extent of reaction of each of the 7 lysyl residues present in alpha A. These results demonstrate that incubation of alpha-crystallins in 0.1 M KNCO leads to partial carbamylation of all 7 lysines of alpha A-crystallin. The extent of modification after 24 h of incubation varied from 7% at Lys 88 to 61% at Lys 11. Rate constants for the reaction of specific lysyl residues with isocyanate ranged from 5 to 54 x 10(-2) M-1 h-1. The distribution of reaction products, as determined by isoelectric focusing, indicates that the physiologically relevant initial stages of carbamylation of the 7 lysyl residues of alpha A proceed in a noncooperative manner.

Modulation of protein kinase C-epsilon by phorbol esters in the monoblastoid U937 cell

Expression of protein kinase C-epsilon was examined in the human monoblastoid U937 cell. This cell type contained the alpha, beta, and epsilon isoforms of protein kinase C (PKC). While PKC-epsilon content was slightly higher in the cytosolic than in the particulate fraction, the amount contained in the particulate fraction was higher than the alpha and beta isoforms which were predominantly localized to the cytosol. After an acute exposure to tetradecanoyl-13-phorbol acetate (TPA), PKC-epsilon translocated to the particulate fraction. Acute or chronic exposure to ionomycin did not alter content of the epsilon isoform. Longer exposures to TPA decreased PKC-epsilon in both cellular fractions. PKC-epsilon displayed a similar sensitivity to TPA-induced down-regulation as did PKC-beta while PKC-alpha was more resistant to this effect. After a 72-h exposure to 0.1 nM TPA, increases in the alpha and beta isoforms but not in PKC-epsilon were observed. However, 1,25-dihydroxy vitamin D3 and dibutyryl cyclic AMP which induce U937 differentiation enhanced PKC-epsilon expression.

Regulation of HMG-CoA reductase, apoprotein-B and LDL receptor gene expression by the hypocholesterolemic drugs simvastatin and ciprofibrate in Hep G2, human and rat hepatocytes

The comparative effects of simvastatin (a competitive inhibitor of HMG-CoA reductase) and ciprofibrate (another inhibitor of cholesterogenesis) on the incorporation of [14C]acetate and [3H]mevalonate into cholesterol HMG-CoA reductase activity, apo-B synthesis, LDL receptor, and their corresponding mRNAs, have been studied in the human hepatoma cell line Hep G2 and in human and rat hepatocytes in primary culture. Incubation of Hep G2 with simvastatin (0.01-1.5 microM) or ciprofibrate (25-100 microM) produced not only a marked inhibition of cholesterogenesis from [14C]acetate but also from [3H]mevalonate, an intermediate downstream of the HMG-CoA reductase reaction. However, in human and rat hepatocytes, cultured in similar conditions, simvastatin inhibited only the cholesterol synthesis from [14C]acetate, as expected. HMG-CoA reductase activity was greatly induced in Hep G2 and rat hepatocytes after incubation with simvastatin (up to 400% of controls), but not with ciprofibrate. Increased enzyme activity was accompanied by a higher cell content of reductase mRNA. Apo-B concentration in the medium of Hep G2 cells was 31% lower after 31 h incubation with simvastatin than in controls. However, neither simvastatin nor ciprofibrate modified the synthesis rate of apo-B or its mRNA level. Both LDL-receptor and its mRNA levels were raised by simvastatin at concentrations inhibiting cholesterol synthesis. Our data show that, in this human hepatoma cell line, HMG-CoA reductase competitive inhibition by simvastatin triggers a coordinate regulation of the expression of genes coding for reductase and LDL receptor but not for apo-B. Ciprofibrate, though efficient in inhibiting cholesterogenesis, did not induce the same regulatory reactions. The reason for this discrepancy is unknown.

[Muscarinic receptor subtypes in respiratory center and their functions]

Radioreceptor binding assays using [3H]quinuclidinyl benzilate and [3H]pirenzepine were performed on the pons and medulla oblongata (MeOb) of rat brain. The M1 cholinergic receptor (M1-R) was found to account for approximately 30-40% of the total muscarinic receptors (M-R) in the pons and MeOb, and the M2 accounted for about 60-70%. The receptor binding capacities of scopolamine and atropine were compared with those of pirenzepine (Pir) and AF-DX 116 on the 2 parts of the brain. The affinity values (pKi) suggest that the selectivity of scopolamine for M1-R is greater than for M2-R, and that of atropine for M2 is greater than for M1. In conscious rabbits, the respiratory frequency (FR), tidal volume (TV), and minute ventilation volume (MVV) were determined. Arterial blood samples were taken intermittently and analyzed for pO2, pCO2, and pH. When pilocarpine (a M1-R subtype selective agonist) was given, excitatory effects on respiration were seen through FR, TV, MVV, and the pO2, pCO2, and pH. When 6 beta-acetoxy nortropane (6 beta-AN, a novel M2-R subtype selective agonist) was given, the effects were inhibitory. These results were reversed after administration of Pir, scopolamine, AF-DX 116, and atropine. Thus, it shows that Pir and scopolamine inhibit respiration by blocking the M1-R subtype of the respiratory center, while the excitatory effects of AF-DX 116 and atropine are brought about by blocking the M2-R subtype of the respiratory center.

Mass spectrometric analysis of the structure of gamma II bovine lens crystallin

The amino acid sequence of bovine gamma II-crystallin has been verified by a combination of electrospray and fast atom bombardment mass spectrometry. The molecular weight of gamma II, isolated by gel filtration and ion exchange chromatography, was determined to be 20,967 +/- 3 by electrospray mass spectrometry. Another aliquot of gamma II was completely digested by trypsin in a medium of 20% CH3CN and 0.1 M Tris, pH 8.2. The tryptic peptides were separated by reversed phase HPLC and identified by their molecular weights, as determined by fast atom bombardment mass spectrometry (FABMS). The identification of each peptide was confirmed by digesting the peptide further to give new peptides whose molecular weights were also determined by FABMS and related to the proposed amino acid sequences. The data from both types of mass spectrometric analyses were consistent with the sequence previously proposed by Hay et al. (J. Biol. Chem. 1987, 146, 332-338), including threonine at position 119. The FAB mass spectrum of one HPLC fraction suggested that disulfide bonding between Cys 18 and Cys 22 was present in at least half the protein preparation. Whether the Cys 18/Cys 22 disulfide bond was present in native gamma II or was produced during isolation or enzymic digestion could not be determined from these studies. Samples that had been stored for several weeks showed that several of the cysteines had become disulfide bonded. These studies illustrate the power of mass spectrometric techniques to accurately confirm the primary structure of proteins and to identify post-translational modifications.

Differential effect of phorbol esters and interleukin-3 on protein kinase C isoform content and kinase activity in the FDC-P1 cell line

FD/PMA is a subclone of the interleukin-3 (IL-3)-dependent, FDC-P1 cell line, which proliferates in response to either 12-O-tetradecanoylphorbol-13 acetate (PMA) or IL-3. While several endogenous substrates were phosphorylated in response to protein kinase C (PKC) activation in FDC-P1, phospholipid-dependent phosphorylation in the FD/PMA grown in PMA was not observed. Basal, phosphatidylserine-independent, and diolein-independent phosphorylation of cytosolic substrates with molecular weights of 17, 52, 57, and 105 Kd were enhanced in FD/PMA cells grown in PMA as compared with FDC-P1 cells cultured in IL-3. Phosphorylation of a 105-Kd substrate was enhanced in the particulate fraction of FD/PMA cells maintained in PMA. The 17-Kd substrate in FD/PMA cells comigrated with a substrate phosphorylated in a PKC-dependent manner in FDC-P1 cells. Phosphorylation of the 52- and 57-Kd substrates, but not of the 17-Kd substrate, was inhibited by H-7 and staurosporine. A portion of the PMA-induced cytosolic kinase activity coeluted with PKC on diethyl aminoethyl chromatography. While FD/PMA cells cultured in PMA contained negligible PKC-dependent phosphorylation of endogenous substrates or histone, alpha and epsilon PKC isoforms were detected by Western blot analysis. PKC phosphotransferase activity was observed in FD/PMA cells grown in PMA when peptides corresponding to residues 720 to 737 of PKC-epsilon or residues 4 to 14 of myelin basic protein were used as substrates. These data indicate that maintenance of FD/PMA cells in PMA stimulates proliferation and markedly alters PKC substrate specificity. Generation of at least two phospholipid-independent kinases occurs in PMA-treated cells.

Determination of the Mark-Houwink equation for chitosans with different degrees of deacetylation

The values of k and alpha in the Mark-Houwink equation have been determined for chitosans with different degrees of deacetylation (DD) (69, 84, 91 and 100% respectively), in 0.2 M CH3COOH/0.1 M CH3COONa aqueous solution at 30 degrees C by the light scattering method. It was shown that the values of alpha decreased from 1.12 to 0.81 and the values of k increased from 0.104 x 10(-3) to 16.80 x 10(-3) ml/g, when the DD varied from 69 to 100%. This is due to a reduction of rigidity of the molecular chain and an increase of the electrostatic repulsion force of the ionic groups along the polyelectrolyte chain in chitosan solution, when the DD of chitosan increases gradually.