A comparison of the antimuscarinic effects of pirenzepine and N-methylatropine on ganglionic and vascular muscarinic receptors in the rat

The antimuscarinic properties of pirenzepine and N-methylatropine were evaluated in two intact preparations by measuring A) the inhibition of increase in mean arterial pressure evoked by McN-A-343 in pithed rats through activation of ganglionic muscarinic receptors and B) the inhibition of fall in arterial pressure evoked by methacholine in anaesthetized rats through activation of vascular muscarinic receptors. To characterize the antimuscarinic potencies of pirenzepine and N-methylatropine, for both antagonists doses were calculated that produce a 10-fold shift to the right of the dose-response curves for A) the pressor response to McN-A-343 (i.v. administration) in pithed rats (D10-p.r.) and B) for the depressor effect to methacholine (i.v. administration) in anaesthetized rats (D10-an.r.), respectively. Whereas N-methylatropine was virtually equieffective in blocking both muscarinic responses (D10-an.r./D10-p.r. approximately equal to 1), pirenzepine, however, was considerably more potent at ganglionic than at vascular muscarinic receptors (D10-an.r./D10-p.r. approximately equal to 16). These data confirm the existence of excitatory ganglionic muscarinic receptors with high affinity for pirenzepine (M1) and provide evidence for the presence of M2 receptors - receptors which show a low sensitivity to pirenzepine - on vascular smooth muscle cells. To further characterize the anticholinergic properties of pirenzepine, its effect on the pressor response to DMPP, a nicotinic ganglionic stimulant, was investigated in pithed rats. A high dose of pirenzepine (1.13 mumol/kg), given i.v., did not affect nicotinic ganglionic transmission.     

Enzymic synthesis,chemical characterisation and Sda activity of GalNAcß1-4[NeuAcα2-3]Galß1-4GlcNAc and GalNAcß1-4[NeuAcα2-3]Galß1-4Glc

The tetrasaccharides GalNAcß1-4[NeuAc2-3]Galß1-4Glc and GalNAcß1-4[NeuAc2-3]Galß1-4GlcNAc were synthesised by enzymic transfer of GalNAc from UDP-GalNAc to 3-sialyllactose (NeuAc2-3Galß1-4Glc) and 3-sialyl-N-acetyllactosamine (NeuAc2-3Galß1-4GlcNAc). The structures of the products were established by methylation and¹H-500 MHz NMR spectroscopy. In Sd^a serological tests the product formed with 3-sialyl-N-acetyllactosamine was highly active whereas that formed with 3-sialyllactose had only weak activity.     

Ouabain-insensitive salt and water movements in duck red cells. II. Norepinephrine stimulation of sodium plus potassium cotransport

Catecholamines induce net salt and water movements in duck red cells incubated in isotonic solutions. The rate of this response is approximately three times greater than a comparable effect observed in 400 mosmol hypertonic solutions in the absence of hormone (W.F. Schmidt and T. J. McManus. 1977 a.J. Gen. Physiol. 70:59-79. Otherwise, these two systems share a great many similarities. In both cases, net water and salt movements have a marked dependence on external cation concentrations, are sensitive to furosemide and insensitive to ouabain, and allow the substitution of rubidium for external potassium. In the presence of ouabain, but the absence of external potassium (or rubidium), a furosemide-sensitive net extrusion of sodium against a large electrochemical gradient can be demonstrated. When norepinephrine-treated cells are incubated with ouabain and sufficient external sodium, the furosemide-sensitive, unidirectional influxes of both sodium and rubidium are half- maximally saturated at similar rubidium concentrations; with saturating external rubidium, the same fluxes are half-maximal at comparable levels of external sodium. In the absence of sodium, a catecholamine-stimulated, furosemide-sensitive influx of rubidium persists. In the absence of rubidium, a similar but smaller component of sodium influx can be seen. We interpret these results in terms of a cotransport model for sodium plus potassium which is activated by hypertonicity or norepinephrine. When either ion is absent from the incubation medium, the system promotes an exchange-diffusion type of movement of the co-ion into the cells. In the absence of external potassium, net movement of potassium out of the cell leads to a coupled extrusion of sodium against its electrochemical gradient.     

Role of conserved threonine and tyrosine residues in acetylcholine binding and muscarinic receptor activation. A study with m3 muscarinic receptor point mutants.

Structure-function relationship studies of the m3 muscarinic acetylcholine receptor have recently identified a series of threonine and tyrosine residues (all located within the hydrophobic receptor core) that are critically involved in acetylcholine binding (Wess, J., Gdula, D., and Brann, M.R. (1991) EMBO J. 10, 3729-3734). To gain further insight into the functional roles of these amino acids, the agonist binding properties of six rat m3 muscarinic receptor point mutants, in which the critical threonine and tyrosine residues had been individually replaced by alanine and phenylalanine, respectively, were studied in greater detail following their transient expression in COS-7 cells. The binding profiles of a series of acetylcholine derivatives suggest that the altered threonine and tyrosine residues are primarily involved in the interaction of the acetylcholine ester moiety with the receptor protein. The two m3 receptor point mutants, Thr234----Ala and Tyr506----Phe, which showed the most pronounced decreases in acetylcholine binding affinities (approximately 40-60-fold as compared with the wild-type receptor), were stably expressed in CHO cells for further functional analysis. Both mutant receptors were found to be severely impaired in their ability to stimulate agonist-dependent phosphatidylinositol hydrolysis. Consistent with this observation, acetylcholine binding to the two mutant receptors was not significantly affected by addition of the GTP analog Gpp(NH)p (5'-guanylyl imidodiphosphate). Our data suggest that Thr234 and Tyr506 (located within transmembrane domains V and VI, respectively), which are conserved among all muscarinic receptors (m1-m5), may play an important role in agonist-induced muscarinic receptor activation.     

Liver-specific drug targeting by coupling to bile acids.

Bile acids are selectively taken up from portal blood into the liver by specific transport systems in the hepatocyte plasma membrane. Therefore, studies were performed to evaluate the potential of bile acids as shuttles to deliver drugs specifically to the liver. The alkylating cytostatic drug chlorambucil and the fluorescent prolyl-4-hydroxylase inhibitor 4-nitrobenzo-2-oxa-1,3-diazol-beta-Ala-Phe-5-oxaproline-Gly were covalently linked via an amide bond to 7 alpha, 12 alpha,-dihydroxy-3 beta- (omega-aminoalkoxy)-5-beta-cholan-24-oic acid. The chlorambucil-bile acid conjugates S 2521, S 2539, S 2567, and S 2576 inhibited Na(+)-dependent [3H]taurocholate uptake in a concentration-dependent manner both into isolated rat hepatocytes and rabbit ileal brush border membrane vesicles, whereas the parent drug chlorambucil showed no significant inhibitory effect. The chlorambucil-bile acid conjugates were able to prevent photoaffinity labeling of bile acid binding proteins in rat hepatocytes by the photolabile [3H]7,7-azo derivative of taurocholic acid indicating their bile acid character. The chlorambucil-bile acid conjugate S 2577 was able to alkylate proteins demonstrating the drug character conserved in the hybrid-molecules. Liver perfusion experiments revealed a secretion profile of the chlorambucil-bile acid conjugate S 2576 into bile very similar to taurocholate compared to chlorambucil which is predominantly excreted by the kidney. 4-Nitrobenzo-2-oxa-1,3-diazol-beta-Ala-Phe-5-oxaproline-Gly- t-butylester (S 4404), a fluorescent peptide inhibitor of prolyl-4-hydroxylase, was not transported in intact form from portal blood into bile in contrast to its bile acid conjugate S 3744; about 25% of the peptide-bile acid conjugate S 3744 was secreted in intact form into bile within 40 min compared with less than 4% of the parent oxaprolylpeptide S 4404. In conclusion, these studies reveal that modified bile acid molecules can be used as "Trojan horses" to deliver a drug molecule specifically into the liver and the biliary system. This offers important pharmacological options for the development of liver-specific drugs.     

In-depth qualitative and quantitative analysis of composite glycosylation profiles and other micro-heterogeneity on intact monoclonal antibodies by high-resolution native mass spectrometry using a modified Orbitrap

Here, we describe a fast, easy-to-use, and sensitive method to profile in-depth structural micro-heterogeneity, including intricate N-glycosylation profiles, of monoclonal antibodies at the native intact protein level by means of mass spectrometry using a recently introduced modified Orbitrap Exactive Plus mass spectrometer. We demonstrate the versatility of our method to probe structural micro-heterogeneity by describing the analysis of three types of molecules: (1) a non-covalently bound IgG4 hinge deleted full-antibody in equilibrium with its half-antibody, (2) IgG4 mutants exhibiting highly complex glycosylation profiles, and (3) antibody-drug conjugates. Using the modified instrument, we obtain baseline separation and accurate mass determination of all different proteoforms that may be induced, for example, by glycosylation, drug loading and partial peptide backbone-truncation. We show that our method can handle highly complex glycosylation profiles, identifying more than 20 different glycoforms per monoclonal antibody preparation and more than 30 proteoforms on a single highly purified antibody. In analyzing antibody-drug conjugates, our method also easily identifies and quantifies more than 15 structurally different proteoforms that may result from the collective differences in drug loading and glycosylation. The method presented here will aid in the comprehensive analytical and functional characterization of protein micro-heterogeneity, which is crucial for successful development and manufacturing of therapeutic antibodies     

Identification of subtypes of muscarinic receptors that regulate Ca2+ and K+ channel activity in sympathetic neurons

Many different G protein-coupled receptors modulate the activity of Ca2+ and K+ channels in a variety of neuronal types. There are five known subtypes (M1-M5) of muscarinic acetylcholine receptors. Knockout mice lacking the M1, M2, or M4 subtypes are studied to determine which receptors mediate modulation of voltage-gated Ca2+ channels in mouse sympathetic neurons. In these cells, muscarinic agonists modulate N- and L-type Ca2+ channels and the M-type K+ channel through two distinct, G-protein mediated pathways. The fast and voltage-dependent pathway is lacking in the M2 receptor knockout mice. The slow and voltage-independent pathway is absent in the M1 receptor knockout mice. Neither pathway is affected in the M4 receptor knockout mice. Muscarinic modulation of the M current is absent in the M1 receptor knockout mice, and can be reconstituted in a heterologous expression system using cloned channels and M1 receptors. Our results using knockout mice are compared with pharmacological data in the rat.     

Use of an in situ disulfide cross-linking strategy to map proximities between amino acid residues in transmembrane domains I and VII of the M3 muscarinic acetylcholine receptor

In this study, we employed an in situ disulfide cross-linking strategy to gain insight into the structure of the inactive and active state of the M(3) muscarinic acetylcholine receptor. Specifically, this study was designed to identify residues in TM I that are located in close to Cys532 (position 7.42), an endogenous cysteine residue present in the central portion of TM VII. Cysteine residues were substituted, one at a time, into 10 consecutive positions of TM I (Ala71-Val80) of a modified version of the M(3) muscarinic receptor that lacked most endogenous cysteine residues and contained a factor Xa cleavage site within the third intracellular loop. Following their expression in COS-7 cells, the 10 resulting cysteine mutant receptors were oxidized in their native membrane environment, either in the absence or in the presence of muscarinic ligands. Disulfide cross-link formation was monitored by examining changes in the electrophoretic mobility of oxidized and factor Xa-digested receptors on SDS gels. When molecular iodine was used as the oxidizing agent, the L77C receptor (position 1.42) was the only mutant receptor that displayed significant disulfide cross-linking, either in the absence or in the presence of muscarinic agonists or antagonists. On the other hand, when the Cu(II)-(1,10-phenanthroline)(3) complex served as the redox catalyst, muscarinic ligands inhibited disulfide cross-linking of the L77C receptor, probably because of impaired access of this relatively bulky oxidizing agent to the ligand binding crevice. The iodine cross-linking data suggest that M(3) muscarinic receptor activation is not associated with significant changes in the relative orientations of the outer and/or central segments of TM I and VII. In bovine rhodopsin, the residues present at the positions corresponding to Cys532 and Leu77 in the rat M(3) muscarinic receptor are not located directly adjacent to each other, raising the possibility that the relative orientations of TM I and VII are not identical among different class I GPCRs. Alternatively, dynamic protein backbone fluctuation may occur, enabling Cys532 to move within cross-linking distance of Leu77 (Cys77).     

The diageotropica mutation alters auxin induction of a subset of the Aux/IAA gene family in tomato

The diageotropica (dgt) mutation has been proposed to affect either auxin perception or responsiveness in tomato plants. It has previously been demonstrated that the expression of one member of the Aux/IAA family of auxin-regulated genes is reduced in dgt plants. Here, we report the cloning of ten new members of the tomato Aux/IAA family by PCR amplification based on conserved protein domains. All of the gene family members except one (LeIAA7) are expressed in etiolated tomato seedlings, although they demonstrate tissue specificity (e.g. increased expression in hypocotyls vs. roots) within the seedling. The wild-type auxin-response characteristics of the expression of these tomato LeIAA genes are similar to those previously described for Aux/IAA family members in Arabidopsis. In dgt seedlings, auxin stimulation of gene expression was reduced in only a subset of LeIAA genes (LeIAA5, 8, 10, and 11), with the greatest reduction associated with those genes with the strongest wild-type response to auxin. The remaining LeIAA genes tested exhibited essentially the same induction levels in response to the hormone in both dgt and wild-type hypocotyls. These results confirm that dgt plants can perceive auxin and suggest that a specific step in early auxin signal transduction is disrupted by the dgt mutation.