[An experimental study on regeneration device for urine and waste water in space station]

The principle, structure and function of the regeneration system for urine and waste water treatment were introduced. The experimental results demonstrated that, the treatment capacity was 1.2-1.9 kg/h, and the regeneration efficiency exceeded 92%. The quality of the treated water were: TOC < 20 g/m3, (NH3 + NH4+) < 10 g/m3, electric conductivity < 100 micro s/cm, pH= 6-8.

Modulation of dimerization by residues distant from the interface in bovine neurophysin-II

The crystal structure of bovine neurophysin-II in its liganded state (Chen et al. [1991] Proc. Natl. Acad. Sci. USA 88, 4240-4244) indicates that the 1-6 sequence has a disordered conformation, lacks noncovalent contacts to other regions of the protein and is distant from the monomer-monomer interface. Cleavage of the 1-6 sequence by Staphylococcus protease V8 yielded a protein that, for the first time, crystallized in both liganded and unliganded states. Insights into the role of the 1-6 sequence in the unliganded state were obtained by NMR and related biophysical comparisons of the native and des-1-6 proteins. NMR spectra demonstrated that the environment and/or conformation of residues in the 1-6 sequence differed in liganded and unliganded states. Additionally, the unliganded des-1-6 protein exhibited a dimerization constant four to five times that of the native protein, potentially accounting for the observation that its peptide affinity was also increased. NMR studies further indicated that the increased dimerization constant of the des-1-6 protein correlated with the presence in the native protein of two isoenergetic forms of the monomer, in contrast to only a single form in the des-1-6 protein, as evidenced by signals from an internal dimerization-sensitive alpha-proton. Thus, the 1-6 sequence reduces the dimerization constant by stabilization of an alternative monomer conformation. A second product of Staphylococcus protease V8 digestion of the native protein was identified as the des-1-6 protein with an internal clip after binding site residue Glu-47, the clip presumably breaking the short 3,10 helix that most directly connects the interface to the interface to the binding site. This product, although unable to bind peptide, retained the dimerization constant of the des-1-6 protein, suggesting a lack of importance of the helix in dimerization and contrasting with the effects of the 1-6 sequence. A model is proposed in which the 1-6 sequence stabilizes the second conformation of the unliganded monomer via interactions affecting the loop region that separates the two neurophysin domains and which has been shown to influence neurophysin self-association.

[Factors for postoperative persistent hypertension in patients with aldosterone-producing adenoma]

We determined the factors for postoperative persistent hypertension in the patients with aldosterone-producing adrenal adenoma (APA) in 53 patients with APA who were followed up for average 3.1 years. All had normal serum potassium concentration postoperatively. Blood pressure was normal in 37 patients (69.8%) but 18.7/12.7 kPa or more in 16 patients (30.2%) with persistent hypertension. Also compared were sex, age, history of hypertension, effect of reducing blood pressure to antisterone, preoperative blood pressure, time of persistent hypertension, serum potassium concentration, aldosterone concentration in 24 hour urine, amount of PRA, and the type of operation. The results showed that an APA patient aged 50 years or more appears to have a great chance of persistent hypertension than an APA patient under age of 40 years, and the odds ratio is 3:1. There was a significant difference between the mean age for persistent hypertension and for normal blood pressure, and varioas response of reducing blood pressure to antisterone (P < 0.05). It is suggested that for an older APA patient and the patient without of reducing blood pressure to antisterone, there are other factors for hypertension such as renal veinlet change or renal interstitial lesions except for hyperaldosteronism. We recommend renal biopsy (using kidney puncture) at the operating table for those patients in order to understand pathological change and guide treatment after operation.

[A new type of reference electrode tube for dynamic monitoring of the acidity in digestive tract]

A new soft Ag-AgCl electrode tube is introduced in this paper. The character test and clinical application show it is especially suitable for dynamic monitoring of the acidity in upper digestive tract.

[Control of blood flow in nasal mucosa by electro-stimulation of sphenopalatine ganglion]

The effects of control of blood flow on cat nasal mucosa by stimulating sphenopalatine ganglion (SPG) were studied using laser Doppler flowmetry in order to investigate the role of SPG. The study showed that the stimulation on one side of SPG could induce vasodilation, with increased blood flow, as well as protective reflexes on both sides. The reactivity depended on the stimulation intensity, frequency and duration. The stimulation on one side of postganglionic parasympathetic nerves, in which the stellate ganglion was resected, caused vasodilation only ipsilaterally. The results indicated that the vasodilation induced by stimulating SPG might be mediated via central reflex arc. The "reverse blood regulation" phenomenon was observed during stimulation of SPG as well. The mechanisms of "reverse blood regulation" induced by stimulating SPG need further investigation.

[The development of long-term dynamic multi-parameter monitoring and analyzing system for upper digestive tract]

A long-term dynamic multi-parameter monitoring and analyzing system for upper digestive tract is presented. The system can record 24-hour pH values of the esophagus and stomach, and necessary ECG data by pressing event key. Hardware and software is described in the paper.

[Measuring EEG complexity for studying the state of mental load]

The complexity defined by Lemple and Ziv (1976) represents the degree of the sequence randomness. In this paper, the complexity of EEG under different mental loads was measured and the relation between the brain active state and the EEG complexity was analyzed. The results showed a statistically strong relation between the mental load and the EEG complexity. Further study showed that the heavier the mental load was the smaller the EEG complexity became. This correlation was especially apparent in the frontal lobe, and the complexity of EEG might be regarded as one of the parameters representing the functional state of the brain. The results indicate that EEG complexity represents the active state of brain in processing information, and the measurement of EEG complexity may provide a new path to the research in the advanced cognitive function of the human brain.

[Materials for joint replacement and friction and wear]

Debilitating diseases such as osteo- and rheumatoid arthritis, trauma and bone cancer can be treated by using prostheses. The wear resistance of materials for joint replacement can affect the service-quality and service-life of prostheses. Materials for joint replacement and friction and wear were briefly reviewed in this paper.

Relations between nasopharyngeal carcinoma and magnesium and other alkaline earth elements in soils in China

Comparison of maps shows a striking geographical relation between high mortality rates from nasopharyngeal cancer in China and low contents of magnesium, calcium and strontium in the soil. We suggest that deficiencies of these elements in the soil could be indirect markers of aetiological factors, e.g. inhalable carcinogens of local natural origin. A search for such factors could be fruitful in further studies of environmental factors in the aetiology of nasopharyngeal carcinoma.

[A fast iterative algorithm for adaptive histogram equalization]

In this paper, we propose an iterative algorthm called FAHE., which is based on the relativity between the current local histogram and the one before the sliding window moving. Comparing with the basic AHE, the computing time of FAHE is decreased from 5 hours to 4 minutes on a 486dx/33 compatible computer, when using a 65 x 65 sliding window for a 512 x 512 with 8 bits gray-level range.

The behavior of the active site salt bridge of bovine neurophysins as monitored by 15N NMR spectroscopy and chemical substitution. Relationship to biochemical properties

The active site of liganded neurophysin contains a salt bridge that involves the side chains of Arg-8 and Glu-47 of the protein and the alpha-amino group of bound hormone or related peptide. The extent to which the Arg-8-Glu-47 salt bridge persists in the absence of peptide, or to which the environment of Arg-8 in the unliganded state differs in monomers and dimers, is relevant to an understanding of allosteric mechanism in this system. In the present study, the behavior of the salt bridge was investigated by 15N NMR and chemical replacement of Arg-8. Bovine neurophysin-I was converted to its des 1-8 derivative, and Arg-8 was replaced by 15N-substituted Arg or by other residues using chemical semisynthesis. The relative abilities of different amino acids to restore peptide affinity to the des 1-8 protein were in good accord with the view of the salt bridge in the liganded state obtained from crystals of bovine neurophysin-II complexes. In the unliganded state, comparison of the 15N and proton NMR signals from Arg-8 with those in smaller arginine systems suggested the absence of significant interactions between the guanidinium of Arg-8 and Glu-47 or between the amino terminal region of Arg-8 and other elements of the protein. No evidence of a difference in Arg-8 environment between unliganded monomers and dimers was found. Marked spectral changes accompanying the binding of oxytocin indicated changes in the environment of both the side chain and amino terminal region of Arg-8. The NMR results were in good agreement with a recently emerging comparison of bovine neurophysin-II derivatives in the liganded and unliganded states, with the notable exception of the extent of salt bridge formation in the unliganded state. The results are shown to be consistent with, and to help explain, significant differences between the two bovine neurophysins in the susceptibility to tryptic cleavage at Arg-8 in the unliganded state and in the pH dependence of peptide binding and additionally constrain potential allosteric mechanisms underlying neurophysin ligand-facilitated dimerization.

[Combustion under microgravity and technique of fire prevention and suppression in space cabin]

This is a brief review on microgravity combustion, along with the discussion of the fundamental characteristics of combustion and fire processes under microgravity. Recent research activities in microgravity combustion and space fire prevention were emphasized. In addition, the potential use of flame-inhibiting atmospheres in the space cabin was introduced. The technique of fire detection and extinguishment in spacecraft environments was also discussed.

The alpha subunit of RNA polymerase and transcription antitermination

The N gene product of coliphage gamma, with a number of host proteins (Nus factors), regulates phage gene expression by modifying RNA polymerase to a form that overrides transcription-termination signals. Mutations in host nus genes diminish this N-mediated antitermination. Here, we report the isolation and characterization of the rpoAD305E mutation, a single amino acid change in the carboxy terminal domain (CTD) of the alpha subunit of RNA polymerase, that enhances N-mediated antitermination. A deletion of the 3' terminus of rpoA, resulting in the expression of an alpha subunit missing the CTD, also enhances N-mediated antitermination and, similar to rpoAD305E, suppresses the effect of nus mutations. Thus, the N-Nus complex may be affected through contacts with the CTD of the alpha subunit of RNA polymerase, as is a group of regulatory proteins that influences initiation of transcription. What distinguishes our findings on the N-Nus complex from those of previous studies with transcription proteins is that all of the regulators characterized in those studies bind DNA and influence transcription initiation; whereas the N-Nus complex binds RNA and affects transcription elongation. A screen of some previously identified rpoA mutations that influence transcription activators revealed only one other amino acid change, L290H, in the CTD of the alpha subunit, that influences antitermination. Although our results provide evidence that interactions of the alpha subunit of RNA polymerase must be considered in forming models of transcription antitermination, they do not provide information as to whether the interactions of alpha that ultimately influence antitermination occur during initiation or during elongation of transcription.

[New use of Bletilla striata as embolizing agent in the intervention treatment of hepatic carcinoma]

A Chinese herb, Bletilla striata, was used as embolizing agent in order to improve the therapeutic results of intervention treatment of liver cancer. From October 1991 to January 1995, 56 cases of hepatic carcinoma were treated with Bletilla striata by hepatic artery embolization, with conventional gelform embolization in 50 cases as control. Patients were followed-up for 10-48 months. Embolization with Bletilla striata led to extensive and permanent vascular obstruction, accompanied with marked shrinkage of tumor size and significant decrease in serum AFP levels. Collaterals were few in number and collateral circulation was established late so that the treatment intervals could be prolonged, with an average of 7 months. The 1-, 2-, and 3-year survival rate was 81.9%, 44.9% and 33.6%, respectively, with a median survival time of 19.8 months. All the clinical parameters were better than those treated with conventional gelform embolization. The results indicate that Bletilla striata is an ideal vascular embolizing agent.

[Quality standard of tanre kesou granules]

A TLC method was used in the identification of the following chemical consitituents of medicinal herbs in Tanre Kesou Granules: Radix Scutellariae, Bulbus Fritillariae Thunbergii, Pericarpium Citri Reticulatae and Fructus Aurantii Immaturus. The sample was purified through acidification with hydrochloric acid and extraction with ethyl acetatethe. The contents of baicalin in the preparation and Radix Scutellariae were determined by means of HPLC and TLC-densitometry. These methods fit for quality control of the preparation containing baicalin.

CNS gene encoding astrotactin, which supports neuronal migration along glial fibers

Vertebrate central nervous system (CNS) histogenesis depends on glia-guided migration of postmitotic neurons to form neuronal laminae. Previous studies have established that the neuronal protein astrotactin functions in murine cerebellar granule cell migration in vitro. The gene encoding astrotactin predicts a protein with three epidermal growth factor repeats and two fibronectin type III repeats. Astrotactin messenger RNA is expressed in postmitotic neuronal precursors in the cerebellum, hippocampus, cerebrum, and olfactory bulb, where migration establishes laminar structures. Fab fragments of antibodies to a recombinant astrotactin peptide blocked migration of cerebellar granule neurons in vitro along astroglial fibers. Transfection of astrotactin complementary DNA into 3T3 cells indicated that astrotactin acts as a ligand for neuron-glia binding during neuronal migration.

Ossiculoplasty by interposition of a minor columella between the tympanic membrane and stapes head

This study analyzes short- and long-term results of 436 ossiculoplasties accomplished by a minor columella sculptured in the remnants of the incus and placed between the tympanic membrane and stapes head. Most cases were operated on by a transcanal approach through an ear speculum, under local anesthesia. Cases in which an associated mastoidectomy was performed to remove diseased tissue are excluded. The residual air-bone gap was < 20 dB in 86.1% of cases 2 months after surgery, in 77.0% 1 year later, and then remained stable over time, even in patients seen 5 to 15 years after the operation. Complications were rare. A total sensorineural hearing loss occurred in two cases (0.4%), the cause of which remained unexplained. Other complications included a high-frequency hearing loss in 10 (2.3%) cases, tinnitus in 12 (2.7%), and transitory vertigo in two (0.4%). We conclude that this type of ossiculoplasty is a simple but adequate procedure for primary restoration of hearing in chronic otitis media if the stapes is intact and mobile.

Characterization of a flow-sorted human chromosome 10 cosmid library by FISH

Fluoresence in situ hybridization (FISH) was used to localize cosmids to regions of human chromosome 10. A total of 301 cosmids were selected randomly from a flow-sorted human chromosome 10 cosmid library constructed from human x hamster cell line 762-8A and arrayed in microtiter storage dishes. Over 70% (211/301) of the cosmids mapped to unique regions of chromosome 10. About 7% (22/301) produced multiple hybridization signals indicative of chimeric clones or sequences repeated at low copy number. Three cosmids (3/301, or 1%) hybridized to the centromeric regions of chromosome 10 and one or more other human chromosomes. About 19% (59/301) consisted mostly or entirely of hamster DNA inserts, and about 2% (6/301) appeared to be nonrecombinants.

Neural network prediction of the HIV-1 protease cleavage sites

A back propagation neural network method has been developed to study the pattern of polypeptides that can be cleaved by the HIV-1 protease. This method can incorporate many characteristics of the peptides, such as hydrophobicity, beta-sheet and alpha-helix propensities. Mutations can also be applied to probe the most important factors that influence the cleavage.

Effect of phorbol ester on cAMP-dependent protein kinase activity in cardiomyocytes

Cardiomyocytes isolated from neonatal rats were treated with phorbol-12-myristate-13-acetate (PMA) ranging from 10(-11) to 10(-7) mol/L for 20 min, causing cytosol protein kinase A (PKA) activity to decrease while particulate PKA activity increase in a concentration-dependent manner. The change of PKA activity induced by PMA was abolished completely by pretreatment of polymyxin B or depletion of protein kinase C (PKC). Type II PKA activity in particulate fraction was enhanced remarkably, while that of type I PKA was not altered when the cells were treated with 100 nmol/L PMA. The results suggested that subcellular distribution and activity of PKA in cardiomyocytes may be regulated by PKC.

[Evaluation of surgical treatment for patients with multiple aldosteronoma: analysis of 11 cases]

From 1957 to 1994, 332 patients underwent surgical treatment for aldosteronoma at Ruijin Hospital. Among them, 11 patients (3.9%) were diagnosed as having multiple aldosteronoma. We ususally used the same method to make the qualitative diagnosis for both single and multiple aldosteronoma. In our experience, however, it was difficult to distinguish the unilateral multiple aldosteronoma by rutine B-type ultrasonography, CT or gamma-scintigraphy before surgery. The correct diagnosis could be obtained only by carefully exploring during the adrenal operation and a satisfactory prognosis also can be acquired if multiple aldosteronoma could be removed completely.

Analysis of the loop-helix interaction in bundle motif protein structures

Molecular dynamics simulations and energy analysis have been carried out to study the structural mobility and stability of the four alpha-helix bundle motifs. The simulation results as well as the X-ray data show that the atomic RMS fluctuation is larger at the loop region for four representative proteins investigated: methemerythrin, cytochrome b-562, cytochrome c', and bovine somatotropin. The loop-loop, helix-helix, and loop-helix interactions are computed for the unfolded and folded proteins. In the folded and solvated protein structures the loop-helix interaction is stronger than the helix-helix interaction, especially in the electrostatic component. But the stabilization energies of both the loop-helix and the helix-helix interactions relative to those of an unfolded structure are of the same order of magnitude. The stabilization due to protein-solvent interaction is greater in the helix region than in the loop region. The percentage of hydrophilic solvent accessible area for the four proteins studied was calculated with the method of Eisenberg and McLachlan. The percentage of the hydrophilic area is greater in the loops than in the helices. A Poisson-Boltzmann calculation shows that the potential from the loops acting on a helix is generally more negative than that from other helices.

[Experimental studies of protective effects of ischemic myocardium preconditioning and its mechanism]

Recent research has shown that repeated brief myocardial ischemia (RBMI) can increase the tolerance of myocardium to a subsequent sustained ischemia and have protective effects on myocardial cells. With the isolated rat heart Langendorff model, we investigated the effects of RBMI on myocardial morphology, systolic function, coronary flow rates (CFR), myocardial membrane phospholipid (PL) content and its marker enzyme's activity (5'-AMPase). The results showed: After ischemia-reflow, the HR, LVP and CFR in control and experimental groups had no significant difference (P > 0.05). But the PL content and specific activity of 5'-AMPase were significantly higher in the experimental group than that in control group (P < 0.01, P < 0.05). And the observations of ultrastructure suggested that the myocardium of the experimental group was preserved better than that in control group. It was also shown that RBMI had protective effects on myocardial membrane structure, and however effective had no relation to CFR.

Detection of ECG characteristic points using wavelet transforms

An algorithm based on wavelet transforms (WT's) has been developed for detecting ECG characteristic points. With the multiscale feature of WT's, the QRS complex can be distinguished from high P or T waves, noise, baseline drift, and artifacts. The relation between the characteristic points of ECG signal and those of modulus maximum pairs of its WT's is illustrated. By using this method, the detection rate of QRS complexes is above 99.8% for the MIT/BIH database and the P and T waves can also be detected, even with serious baseline drift and noise.

Reduced Rho-dependent transcription termination permits NusA-independent growth of Escherichia coli

NusA and Rho are essential Escherichia coli proteins that influence transcription elongation and termination. We show that an E. coli derivative unable to express NusA, because its sole nusA gene contains a large deletion/substitution, is viable providing that the bacterium also carries a rho mutation that reduces transcription termination. This Rho-mediated suppression is not allele specific, since either a mutation changing amino acid 134 [rho(E134D)] or a mutation changing amino acid 352 (rho1) allows growth of a nusA-deleted E. coli. However, both rho mutations similarly decrease transcription termination 8- to 9-fold. We propose that the essential role of NusA is to enhance pausing of RNA polymerase at certain sites, permitting tight coupling of transcription and translation. This coupling interferes with Rho access to and/or movement on the nascent RNA and blocks premature termination of transcription. Thus, NusA-dependent coupling should be less important in a mutant with low Rho activity. The fact that E. coli grows without NusA argues that NusA should be considered an accessory factor rather than a subunit of RNA polymerase.

Escherichia coli-Salmonella typhimurium hybrid nusA genes: identification of a short motif required for action of the lambda N transcription antitermination protein

The Escherichia coli nusA gene, nusAEc, encodes an essential protein that influences transcription elongation. Derivatives of E. coli in which the Salmonella typhimurium nusA gene, nusASt, has replaced nusAEc are viable. Thus, NusASt can substitute for NusAEc in supporting essential bacterial activities. However, hybrid E. coli strains with the nusASt substitution do not effectively support transcription antitermination mediated by the N gene product of phage lambda. We report the DNA sequence of nusASt, showing that the derived amino acid sequence is 95% identical to the derived amino acid sequence of nusAEc. The alignment of the amino acid sequences reveals scattered single amino acid differences and one region of significant heterogeneity. In this region, called 449, NusAEc has four amino acids and NusASt has nine amino acids. Functional studies of hybrid nusA genes, constructed from nusAEc and nusASt, show that the 449 region of the NusAEc protein is important for lambda N-mediated transcription antitermination. A hybrid that has a substitution of the four E. coli codons for the nine S. typhimurium codons, but is otherwise nusASt, supports the action of the N antitermination protein. The 449 region and, presumably, adjacent sequences appear to compose a functional domain of NusAEc important for the action of the N transcription antitermination protein of phage lambda.

Molecular origin of the internal dipole potential in lipid bilayers: calculation of the electrostatic potential

The finite difference linearized Poisson-Boltzmann equation was solved for a segment of bilayer for two lipids (phosphatidylcholine dihydrate and phosphatidylethanolamine-acetic acid) in order to obtain the transbilayer electrostatic potential. Atomic coordinates derived from the crystal structures of these lipids were used, and partial changes were assigned to all atoms in the polar parts of the molecules. These calculations confirmed that a dipole potential exists in the uncharged hydrophobic interior of a bilayer. The phosphocholine and phosphoethanolamine groups make negative contributions to the internal potential, and the glycerol acyl esters make positive contributions, but the sum of these terms is negative. The water of hydration in phosphatidylcholine, and the acetic acid which is present in the phosphatidylethanolamine crystal structure, make positive contributions to the internal potential. It is concluded that the water of hydration in fully hydrated lipid bilayers is mainly responsible for the experimentally inferred positive sign of the internal potential.

Strong electrostatic loop-helix interactions in bundle motif protein structures

Based on CHARMM potential (Brooks et al., 1983) an energetic analysis has been carried out for four typical 4-alpha-helix bundle proteins, i.e., methemerythrin, cytochrome b-562, cytochrome c', and bovine somatotropin. The bovine somatotropin possesses long loops, but all the other three proteins have short loops. It was found that in all these four 4-alpha-helix bundle motif structures the interaction between loops and helices was much stronger than the interaction among the four helices themselves. Particularly for the electrostatic interaction energy, the loop-helix interaction is overwhelmingly stronger than the interhelix interaction although the latter involves the favorable helix dipole interaction due to the antiparallel arrangement of neighboring alpha-helices. The present study indicates that such a conclusion holds true regardless of what loops, long or short, are in the 4-alpha-helix bundle protein, and also regardless of which empirical potential, ECEPP or CHARMM, is used for calculations although in CHARMM the electrostatic energy is much more heavily emphasized than in ECEPP. Therefore, no appropriate conclusion can be drawn in arguing whether the dipole interaction among the four alpha-helices play a stabilizing role or destabilizing role for a 4-alpha-helix bundle protein without taking into consideration the effect of interaction between helices and loops. The calculated results reported here provide, from a different point of view, insights that might be useful for revealing the essence of the driving forces during the folding of proteins.

Time frequency distributions of TMJ sounds

For analysis of time-varying signals such as the TMJ sounds, it is often desirable to know how the frequency components change with time, using methods of time-frequency analysis. The aim of this study was to compare two of the most familiar methods for energy density representation with a newly developed technique. The sounds were recorded with a microphone fastened to the subject's forehead, transformed to the time-frequency domain and displayed as 3D- and contour plots using spectrogram, Wigner distribution (WD), and the reduced interference distribution (RID) to display their time-frequency energy distributions. The spectrogram resolved only the low-frequency components. The WD provided higher resolution but also exhibited strong interference between components. The RID gave a detailed representation of the TMJ signals' relative energy distribution in the time and frequency domains, with a great reduction in the interference or cross terms. The RID therefore appears to be most useful in the application of time-frequency distributions in classification of TMJ sounds.

Quantum simulation of ferrocytochrome c

The dramatic progress in the understanding of the dynamics of biomolecules has been largely fuelled by computer simulations based on the law of classical mechanics. However in some respects biomolecules are at the borders of the domain of applicability of classical mechanics. The role of quantum mechanical effects in biomolecular structure and function is therefore worth investigating. Here we present preliminary results from a quantum simulation of a protein and contrast them with results from full classical simulations. The most significant differences are found in motions of high frequency, such as bond stretching or the torsional oscillation of groups that bear hydrogen atoms. The amplitudes of such motions are significantly increased by the penetration of atoms into classically forbidden regions. These differences will directly influence the rates of such processes as proton and electron transfer.

Inhibitory effect of methacholine on drug-induced relaxation, cyclic AMP accumulation, and cyclic AMP-dependent protein kinase activation in canine tracheal smooth muscle

Functional antagonism between bronchoconstricting and bronchodilating pathways was examined in canine tracheal smooth muscle. Trachealis strips were contracted with either 0.3 microM (EC55) or 3.0 microM (EC80) methacholine before being relaxed by the cumulative addition of isoproterenol, prostaglandin E2, or forskolin. The EC50 for all three relaxants was increased 10-fold in tissues contracted with 3.0 microM methacholine vs. those contracted with 0.3 microM methacholine. Moreover, contracting tissues with the higher concentration of methacholine reduced the maximum relaxation induced by prostaglandin E2 and isoproterenol. Forskolin produced total relaxation regardless of the concentration of methacholine used and thus was a much more effective bronchodilator than either isoproterenol or prostaglandin E2. The inhibitory effect of methacholine on the relaxant response to these agents was paralleled by a reduction in drug-stimulated cyclic AMP-dependent protein kinase activity. Methacholine reduced the maximum activation of cyclic AMP-dependent protein kinase elicited by isoproterenol, prostaglandin E2 and submaximal concentrations of forskolin, which was a much more powerful enzyme activator than the other two agents. The ability of a maximum concentration of forskolin (30 microM) to activate cyclic AMP-dependent protein kinase was not inhibited by methacholine. Although methacholine also appeared to suppress drug-stimulated cyclic AMP accumulation, the inhibitory effect was only statistically significant in forskolin-treated tissues.(ABSTRACT TRUNCATED AT 250 WORDS)