The performance of tongue swabs for detection of pulmonary tuberculosis

Introduction

Oral and/or tongue swabs have demonstrated ability to detect Mycobacterium tuberculosis (Mtb) in adults with pulmonary tuberculosis (TB). Swabs provide useful alternative specimens for diagnosis of TB using molecular assays however, the diagnostic pickup by culture requires further improvement and development. Several studies identified the presence of differentially culturable tubercle bacilli (DCTB) populations in a variety of clinical specimens. These organisms do not grow in routine laboratory media and require growth factors in the form of culture filtrate (CF) from logarithmic phase cultures of Mtb H37Rv.

Methods

Herein, we compared the diagnostic performance of sputum and tongue swabs using Mycobacterial Growth Indicator Tube (MGIT) assays, Auramine smear, GeneXpert and DCTB assays supplemented with or without CF.

Results

From 89 eligible participants, 83 (93%), 66 (74%) and 79 (89%) were sputum positive by MGIT, smear and GeneXpert, respectively. The corresponding tongue swabs displayed a lower sensitivity with 39 (44%), 2 (2.0%) and 18 (20%) participants respectively for the same tests. We aimed to improve the diagnostic yield by utilizing DCTB assays. Sputum samples were associated with a higher positivity rate for CF-augmented DCTB at 82/89 (92%) relative to tongue swabs at 36/89 (40%). Similarly, sputum samples had a higher positivity rate for DCTB populations that were CF-independent at 64/89 (72%) relative to tongue swabs at 26/89 (29%). DCTB positivity increased significantly, relative to MGIT culture, for tongue swabs taken from HIV-positive participants. We next tested whether the use of an alternative smear stain, DMN-Trehalose, would improve diagnostic yield but noted no substantial increase.

Discussion

Collectively, our data show that while tongue swabs yield lower bacterial numbers for diagnostic testing, the use of growth supplementation may improve detection of TB particularly in HIV-positive people but this requires further interrogation in larger studies.

Differentially culturable tubercle bacteria as a measure of tuberculosis treatment response

Introduction

Routine efficacy assessments of new tuberculosis (TB) treatments include quantitative solid culture or routine liquid culture, which likely miss quantification of drug tolerant bacteria. To improve these assessments, comparative analyses using additional measures such as quantification of differentially culturable tubercle bacteria (DCTB) are required. Essential for enabling this is a comparative measure of TB treatment responses using routine solid and liquid culture with liquid limiting dilutions (LLDs) that detect DCTB in sputum.

Methods

We recruited treatment-naïve TB patients, with and without HIV-infection, and serially quantified their sputum for DCTB over the course of treatment.

Results

Serial sputum sampling in 73 individuals during their first 14 days of treatment demonstrated that clearance of DCTB was slower compared to routine solid culture. Treatment response appeared to be characterized by four patterns: (1) Classic bi-phasic bacterial clearance; (2) early non-responders with slower clearance; (3) paradoxical worsening with an increase in bacterial count upon treatment initiation; and (4) non-responders with no change in bacterial load. During treatment, LLDs displayed greater bacterial yield when compared with quantitative solid culture. Upon treatment completion, 74% [46/62] of specimens displayed residual DCTB and within this group, two recurrences were diagnosed. Residual DCTB upon treatment completion was associated with a higher proportion of MGIT culture, GeneXpert, and smear positivity at two months post treatment. No recurrences occurred in the group without residual DCTB.

Discussion

These data indicate that DCTB assays detect distinct subpopulations of organisms in sputum that are missed by routine solid and liquid culture, and offer important alternatives for efficacy assessments of new TB treatments. The residual DCTB observed upon treatment completion suggests that TB treatment does not always eliminate all bacterial populations, a finding that should be investigated in larger cohorts.

Detection of differentially culturable tubercle bacteria in sputum using mycobacterial culture filtrates

Rapid detection of tuberculosis (TB) infection is paramount to curb further transmission. The gold standard for this remains mycobacterial culture, however emerging evidence confirms the presence of differentially culturable tubercle bacteria (DCTB) in clinical specimens. These bacteria do not grow under standard culture conditions and require the presence of culture filtrate (CF), from axenic cultures of Mycobacterium tuberculosis (Mtb), to emerge. It has been hypothesized that molecules such as resuscitation promoting factors (Rpfs), fatty acids and cyclic-AMP (cAMP) present in CF are responsible for the growth stimulatory activity. Herein, we tested the ability of CF from the non-pathogenic bacterium Mycobacterium smegmatis (Msm) to stimulate the growth of DCTB, as this organism provides a more tractable source of CF. We also interrogated the role of Mtb Rpfs in stimulation of DCTB by creating recombinant strains of Msm that express Mtb rpf genes in various combinations. CF derived from this panel of strains was tested on sputum from individuals with drug susceptible TB prior to treatment. CF from wild type Msm did not enable detection of DCTB in a manner akin to Mtb CF preparations and whilst the addition of RpfAB^Mtb and RpfABCDE^Mtb to an Msm mutant devoid of its native rpfs did improve detection of DCTB compared to the no CF control, it was not statistically different to the empty vector control. To further investigate the role of Rpfs, we compared the growth stimulatory activity of CF from Mtb, with and without Rpfs and found these to be equivalent. Next, we tested chemically diverse fatty acids and cAMP for growth stimulation and whilst some selective stimulatory effect was observed, this was not significantly higher than the media control and not comparable to CF. Together, these data indicate that the growth stimulatory effect observed with Mtb CF is most likely the result of a combination of factors. Future work aimed at identifying the nature of these growth stimulatory molecules may facilitate improvement of culture-based diagnostics for TB.

Genetic Diversity in Mycobacterium tuberculosis Clinical Isolates and Resulting Outcomes of Tuberculosis Infection and Disease

Tuberculosis claims more human lives than any other bacterial infectious disease and represents a clear and present danger to global health as new tools for vaccination, treatment, and interruption of transmission have been slow to emerge. Additionally, tuberculosis presents with notable clinical heterogeneity, which complicates diagnosis, treatment, and the establishment of nonrelapsing cure. How this heterogeneity is driven by the diversity ofclinical isolates of the causative agent, Mycobacterium tuberculosis, has recently garnered attention. Herein, we review advances in the understanding of how naturally occurring variation in clinical isolates affects transmissibility, pathogenesis, immune modulation, and drug resistance. We also summarize how specific changes in transcriptional responses can modulate infection or disease outcome, together with strain-specific effects on gene essentiality. Further understanding of how this diversity of M. tuberculosis isolates affects disease and treatment outcomes will enable the development of more effective therapeutic options and vaccines for this dreaded disease.

Rapid detection of Mycobacterium tuberculosis in sputum with a solvatochromic trehalose probe

Tuberculosis (TB) is the leading cause of death from an infectious bacterial disease. Poor diagnostic tools to detect active disease plague TB control programs and affect patient care. Accurate detection of live Mycobacterium tuberculosis (Mtb), the causative agent of TB, could improve TB diagnosis and patient treatment. We report that mycobacteria and other corynebacteria can be specifically detected with a fluorogenic trehalose analog. We designed a 4-N,N-dimethylamino-1,8-naphthalimide-conjugated trehalose (DMN-Tre) probe that undergoes >700-fold increase in fluorescence intensity when transitioned from aqueous to hydrophobic environments. This enhancement occurs upon metabolic conversion of DMN-Tre to trehalose monomycolate and incorporation into the mycomembrane of Actinobacteria. DMN-Tre labeling enabled the rapid, no-wash visualization of mycobacterial and corynebacterial species without nonspecific labeling of Gram-positive or Gram-negative bacteria. DMN-Tre labeling was detected within minutes and was inhibited by heat killing of mycobacteria. Furthermore, DMN-Tre labeling was reduced by treatment with TB drugs, unlike the clinically used auramine stain. Lastly, DMN-Tre labeled Mtb in TB-positive human sputum samples comparably to auramine staining, suggesting that this operationally simple method may be deployable for TB diagnosis.

Alteration in propagating colonic contractions by dairy proteins in isolated rat large intestine

Gastrointestinal conditions in which the transit of contents is altered may benefit from nutritional approaches to influencing health outcomes. Milk proteins modulate the transit of contents along different regions, suggesting that they have varying effects on neuromuscular function to alter gastrointestinal motility. We tested the hypothesis that bovine whey and casein milk protein hydrolysates could have direct modulatory effects on colonic motility patterns in isolated rat large intestine. Casein protein hydrolysate (CPH), whey protein concentrate (WPC), whey protein hydrolysate (WPH), and a milk protein hydrolysate (MPH; a hydrolyzed blend of 60% whey to 40% casein) were compared for their effects on spontaneous contractile waves. These contractions propagate along the length of the isolated intact large intestine (22 cm) between the proximal colon and rectum and were detected by measuring activity at 4 locations. Milk proteins were perfused through the tissue bath, and differences in contraction amplitude and frequency were quantified relative to pretreatment controls. Propagation frequency was decreased by CPH, increased by MPH, and unaffected by intact whey proteins. The reduced motility with CPH and increased motility with MPH indicate a direct action of these milk proteins on colon tissue and provide evidence for differential modulation by hydrolysate type. These findings mirror actions on lower gastrointestinal transit reported in vivo, with the exception of WPH, suggesting that other factors are required.

Advances in the understanding of Mycobacterium tuberculosis transmission in HIV-endemic settings

Tuberculosis claims more human lives than any other infectious disease. This alarming epidemic has fuelled the development of novel antimicrobials and diagnostics. However, public health interventions that interrupt transmission have been slow to emerge, particularly in HIV-endemic settings. Transmission of tuberculosis is complex, involving various environmental, bacteriological, and host factors, among which concomitant HIV infection is important. Preventing person-to-person spread is central to halting the epidemic and, consequently, tuberculosis transmission is now being studied with renewed interest. In this Series paper, we review recent advances in the understanding of tuberculosis transmission, from the view of source-case infectiousness, inherent susceptibility of exposed individuals, appending tools for predicting risk of disease progression, the biophysical nature of the contagion, and the environments in which transmission occurs and is sustained in populations. We focus specifically on how HIV infection affects these features with a view to describing novel transmission blocking strategies in HIV-endemic settings.

Identification of Quantitative Proteomic Differences between Mycobacterium tuberculosis Lineages with Altered Virulence

Evidence currently suggests that as a species Mycobacterium tuberculosis exhibits very little genomic sequence diversity. Despite limited genetic variability, members of the M. tuberculosis complex (MTBC) have been shown to exhibit vast discrepancies in phenotypic presentation in terms of virulence, elicited immune response and transmissibility. Here, we used qualitative and quantitative mass spectrometry tools to investigate the proteomes of seven clinically-relevant mycobacterial strains—four M. tuberculosis strains, M. bovis, M. bovis BCG, and M. avium—that show varying degrees of pathogenicity and virulence, in an effort to rationalize the observed phenotypic differences. Following protein preparation, liquid chromatography mass spectrometry (LC MS/MS) and data capture were carried out using an LTQ Orbitrap Velos. Data analysis was carried out using a novel bioinformatics strategy, which yielded high protein coverage and was based on high confidence peptides. Through this approach, we directly identified a total of 3788 unique M. tuberculosis proteins out of a theoretical proteome of 4023 proteins and identified an average of 3290 unique proteins for each of the MTBC organisms (representing 82% of the theoretical proteomes), as well as 4250 unique M. avium proteins (80% of the theoretical proteome). Data analysis showed that all major classes of proteins are represented in every strain, but that there are significant quantitative differences between strains. Targeted selected reaction monitoring (SRM) assays were used to quantify the observed differential expression of a subset of 23 proteins identified by comparison to gene expression data as being of particular relevance to virulence. This analysis revealed differences in relative protein abundance between strains for proteins which may promote bacterial fitness in the more virulent W. Beijing strain. These differences may contribute to this strain's capacity for surviving within the host and resisting treatment, which has contributed to its rapid spread. Through this approach, we have begun to describe the proteomic portrait of a successful mycobacterial pathogen. Data are available via ProteomeXchange with identifier PXD004165.

Lotus corniculatus condensed tannins decrease in vivo populations of proteolytic bacteria and affect nitrogen metabolism in the rumen of sheep

Condensed tannins in forage legumes improve the nutrition of sheep by reducing ruminal degradation of plant protein and increasing crude protein flow to the intestine. However, the effects of condensed tannins in forage legumes on rumen bacterial populations in vivo are poorly understood. The aim of this study was to investigate the specific effects of condensed tannins from Lotus corniculatus on four proteolytic rumen bacteria in sheep during and after transition from a ryegrass (Lolium perenne)-white clover (Trifolium repens) diet (i.e., low condensed tannins) to a Lotus corniculatus diet (i.e., higher condensed tannins). The bacterial populations were quantified using a competitive polymerase chain reaction. Lotus corniculatus was fed with or without ruminal infusions of polyethylene glycol (PEG), which binds to and inactivates condensed tannins, enabling the effect of condensed tannins on bacterial populations to be examined. When sheep fed on ryegrass-white clover, populations of Clostridium proteoclasticum B316T, Butyrivibrio fibrisolvens C211a, Eubacterium sp. C12b, and Streptococcus bovis B315 were 1.5 x 10(8), 1.1 x 10(6), 4.6 x 10(8), and 7.1 x 10(6) mL(-1), respectively. When the diet was changed to Lotus corniculatus, the average populations (after 8-120 h) of C. proteoclasticum, B. fibrisolvens, Eubacterium sp., and S. bovis decreased (P < 0.001) to 2.4 x 10(7), 1.1 x 10(5), 1.1 x 10(8), and 2.5 x 10(5) mL(-1), respectively. When PEG was infused into the rumen of sheep fed Lotus corniculatus, the populations of C. proteoclasticum, B. fibrisolvens, Eubacterium sp., and S. bovis were higher (P < 0.01-0.001) than in sheep fed Lotus corniculatus without the PEG infusion, with average populations (after 8-120 h) of 4.9 x 10(7), 3.8 x 10(5), 1.9 x 10(8), and 1.0 x 10(6), respectively. Sheep fed the Lotus corniculatus diet had lower rumen proteinase activity, ammonia, and soluble nitrogen (P < 0.05-0.001) than sheep that were fed Lotus corniculatus plus PEG. The Lotus corniculatus diet reduced rumen nitrogen digestibility (P < 0.05) and ammonia pool size and increased the flow of undegraded feed nitrogen to the abomasum. The nitrogen intake, rumen non-ammonia nitrogen pool size, rumen microbial non-ammonia nitrogen pool size, and abomasal microbial non-ammonia nitrogen fluxes were similar both in sheep fed only Lotus corniculatus and in sheep fed Lotus corniculatus plus PEG, but nonmicrobial non-ammonia nitrogen flux to the abomasum was higher (P < 0.01) for the sheep fed only Lotus corniculatus. Although condensed tannins in Lotus corniculatus reduced the populations of some proteolytic bacteria, total ruminal microbial protein and microbial protein outflow to the abomasum were unchanged, suggesting a species-specific effect of condensed tannins on bacteria in the rumen.

Experience with the holmium laser as an endoscopic lithotrite

INTRODUCTION

Holmium laser lithotripsy represents an additional option in the management of urinary tract calculi. We report the results of a cohort of patients with ureteric and bladder calculi treated with this modality.

METHODS

Twenty-three patients underwent holmium laser lithotripsy to treat ureteric or bladder calculi. Power settings of 0.5 J to deliver 2.5-4.0 watts were used for the ureteric calculi, and up to 30 watts for the bladder calculi.

RESULTS

The mean ureteric stone size was 7.3 mm (range 4-10 mm). One stone was upper ureteric, seven were mid-ureter and nine were lower-ureter. Eighteen of the 19 patients with ureteric calculi were free of stones 28 days postoperatively. The remaining patient was clear by 12 weeks. All patients with bladder calculi were completely cleared of stones. There were no intraoperative complications.

DISCUSSION

Ureteric stone position can limit the use of extracorporeal shock wave lithotripsy due to imaging difficulties. Ureteric lithotripsy overcomes this problem. The holmium laser has proven to be safe and effective in clearing urinary stone burdens of a variety of sizes, sites and compositions in this cohort of patients.

Granular cell tumor of the toe

A 33-year-old black woman with an unusual case of a solitary granular cell tumor (GCT) involving the toe is presented, as is a review of the literature. The clinical presentation, histopathologic appearance, differential diagnosis, and treatment of solitary granular cell tumors are discussed. GCTs are uncommon tumors and are thought to be of Schwann cell origin. These tumors usually present as reddish-brown to flesh-colored papules that are occasionally tender or pruritic. The surface is usually smooth, but may be ulcerated or verrucous. Although they are usually solitary, they may be multiple. These tumors are almost always benign, but malignant variants have been reported. Predilection is greatest in females, and blacks are affected several times more often than whites. The skin overlying the face, trunk, fingers, and mucous membranes account for the vast majority of reported cases.

Pectin methylesterase regulates methanol and ethanol accumulation in ripening tomato (Lycopersicon esculentum) fruit

We provide genetic evidence that the production of methanol in tomato fruit is regulated by pectin methylesterase (PME, EC 3.1.1.11), an enzyme that catalyzes demethoxylation of pectins. The role of PME in methanol production in tomato fruit was examined by relating the tissue methanol content to the PME enzymatic activity in wild-type Rutgers and isogenic PME antisense fruits with lowered PME activity. In the wild-type, fruit development and ripening were accompanied by an increase in the abundance of PME protein and activity and a corresponding ripening-related increase in methanol content. In the PME antisense pericarp, the level of methanol was greatly reduced in unripe fruit, and diminished methanol content persisted throughout the ripening process. The close correlation between PME activity and levels of methanol in fruit tissues from wild-type and a PME antisense mutant indicates that PME is the primary biosynthetic pathway for methanol production in tomato fruit. Interestingly, ethanol levels that were low and unchanged during ripening of wild-type tomatoes increased progressively with the ripening of PME antisense fruit. In vitro studies indicate that methanol is a competitive inhibitor of the tomato alcohol dehydrogenase (ADH, EC 1.1.1.1) activity suggesting that ADH-catalyzed production of ethanol may be arrested by methanol accumulation in the wild-type but not in the PME mutant where methanol levels remain low.

The effect of condensed tannins in Lotus pedunculatus on the solubilization and degradation of ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39; Rubisco) protein in the rumen and the sites of Rubisco digestion

Three experiments were undertaken to determine the effect of condensed tannin (CT) in Lotus pedunculatus (45-55 g extractable CT/kg DM) on the digestion of the principal leaf protein, ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39; Rubisco; fraction 1 leaf protein). In two of the experiments Lotus pedunculatus was fed to sheep, with one group receiving a continuous intraruminal infusion (per fistulum) of PEG (molecular weight 3500) to bind and inactivate the CT (PEG group). The other group, which did not receive PEG, was termed the control sheep (CT acting). Expt 3 involved in vitro incubations of Lotus pedunculatus in buffered rumen fluid, with and without PEG added. In all experiments the results have been interpreted in terms of the effects of CT on Rubisco solubilization and degradation. Disappearance of N and Rubisco from Lotus pedunculatus suspended in polyester bags in the rumen was used as a measure of solubilization. Degradation was defined as the disappearance of Rubisco from in vitro incubations of Lotus pedunculatus in rumen fluid. In Expt 1, CT reduced the digestion of Rubisco in the rumen from 0.96 to 0.72 of intake (P < 0.01). Rubisco digestion in the small intestine was 0.27 of intake in control sheep and 0.04 of intake in PEG sheep. In Expt 2, PEG had no effect on the loss of Rubisco from Lotus pedunculatus contained in polyester bags which were incubated in the rumen, hence CT did not affect the solubilization of Rubisco. Observations in Expt 1 were confirmed by in vitro incubations in Expt 3, where PEG addition substantially increased the rate of degradation of plant protein to NH3. Addition of PEG decreased the period of time taken to degrade 50% of the Rubisco from about 13.8 h to about 3.0 h. It was concluded that the action of CT reduced the digestion of Rubisco in the rumen of sheep fed on fresh Lotus pedunculatus, and that this was primarily due to the ability of CT to slow its degradation by rumen micro-organisms, without affecting its solubilization. Both fresh-minced, and freeze-dried and ground lotus were used for in sacco and in vitro incubations; however, fresh-minced lotus was more suitable for the evaluation of protein solubilization and degradation in fresh forages.

Endoscopic treatment of a giant ileal conduit calculus

A giant ileal conduit calculus is an uncommon complication of urinary diversion, with few recent reports present in the English literature. To date all described instances have necessitated treatment by laparotomy. The first reported successful management of such a condition by purely endoscopic means is reported.

Characterization of a chloroplast inner envelope K+ channel

A K(+)-conducting protein of the chloroplast inner envelope was characterized as a K+ channel. Studies of this transport protein in the native membrane documented its sensitivity to K+ channel blockers. Further studies of native membranes demonstrated a sensitivity of K+ conductance to divalent cations such as Mg2+, which modulate ion conduction through interaction with negative surface charges on the inner-envelope membrane. Purified chloroplast inner-envelope vesicles were fused into an artificial planar lipid bilayer to facilitate recording of single-channel K+ currents. These single-channel K+ currents had a slope conductance of 160 picosiemens. Antibodies generated against the conserved amino acid sequence that serves as a selectivity filter in the pore of K+ channels immunoreacted with a 62-kD polypeptide derived from the chloroplast inner envelope. This polypeptide was fractionated using density gradient centrifugation. Comigration of this immunoreactive polypeptide and K+ channel activity in sucrose density gradients further suggested that this polypeptide is the protein facilitating K+ conductance across the chloroplast inner envelope.

K+-conducting ion channel of the chloroplast inner envelope: functional reconstitution into liposomes

Potassium flux between the chloroplast stroma and cytoplasm is known to be indirectly linked to H+ countertransport and, hence, stromal pH and photosynthetic capacity. The specific molecular mechanism that facilitates K+ flux across the chloroplast envelope is not known and has been a source of controversy for well over a decade. The objective of this study was to elucidate the nature of this envelope protein. To this end, solubilized protein in detergent extracts of purified chloroplast inner envelope vesicles was reconstituted into artificial liposomes, and cation fluxes into these proteoliposomes were measured. Results of inhibitor studies and counterflux experiments indicated that a K+-conducting ion channel was solubilized and functionally reconstituted into the proteoliposomes. This transport protein may be a nonspecific monovalent cation channel. This report represents a direct demonstration of ion channel activity associated with the limiting (inner) membrane of the chloroplast envelope.

The management of renal cell carcinoma with inferior vena-caval involvement

Seven patients with renal cell carcinoma involving the inferior vena cava underwent surgical resection between 1975 and 1991. Pre-operative staging defined five patients with stage T3bNoMo disease, one patient with stage T3bN1Mo, and one patient with stage T3bNoM1 disease. At operation one patient had tumour thrombus filling the right atrium. Two patients had tumour thrombus within the intrahepatic vena cava and four infrahepatic tumour thrombus. The mean follow-up is 34.4 months (median 40 months). Four patients have been followed for over 4 years. Three of these patients are survivors, two have remained disease-free since their initial surgery. The other patient had a liver resection at 49 months for a solitary metastases; he is currently disease free. One patient died at 38 months from a gastrointestinal haemorrhage. Three patients are 12 months or less postoperation. Operative mortality was zero. The mean postoperative hospital stay was 14.7 days. Data suggests that 3-10% of renal cell carcinomas will involve the inferior vena cava. The small number of patients in this series suggests that many patients with renal cell carcinoma involving the inferior vena cava are not referred for surgical assessment. These patients are potential surgical candidates. Their survival after surgical resection, excluding the group with extension of tumour thrombus into the hepatic cava or above, is not reduced when compared with other patients with renal carcinoma.

Experience with the pulsed dye laser in management of ureteric calculi

Pulsed dye laser lithotripsy is a recently developed technique for the management of urinary calculi. This article reports the results of treatment of a cohort of patients managed with this technology. Post-treatment bed stay was generally less than 48 h, narcotic analgesia was not regularly required, and no significant post-treatment complications were encountered. This treatment appeared to complement an existing extracorporeal shockwave lithotripsy (ESWL) service at St Vincent's Hospital and may offer a financial advantage in the treatment of patients with urinary calculi.

Studies on the System Regulating Proton Movement across the Chloroplast Envelope : Effects of ATPase Inhibitors, Mg, and an Amine Anesthetic on Stromal pH and Photosynthesis

Studies were undertaken to further characterize the spinach (Spinacea oleracea) chloroplast envelope system, which facilitates H(+) movement into and out of the stroma, and, hence, modulates photosynthetic activity by regulating stromal pH. It was demonstrated that high envelope-bound Mg(2+) causes stromal acidification and photosynthetic inhibition. High envelope-bound Mg(2+) was also found to necessitate the activity of a digitoxinand oligomycin-sensitive ATPase for the maintenance of high stromal pH and photosynthesis in the illuminated chloroplast. In chloroplasts that had high envelope Mg(2+) and inhibited envelope ATPase activity, 2-(diethylamino)-N-(2,6-dimethylphenyl)acetamide was found to raise stromal pH and stimulate photosynthesis. 2-(Diethylamino)-N-(2,6-dimethylphenyl)acetamide is an amine anesthetic that is known to act as a monovalent cation channel blocker in mammalian systems. We postulate that the system regulating cation and H(+) fluxes across the plastid envelope includes a monovalent cation channel in the envelope, some degree of (envelope-bound Mg(2+) modulated) H(+) flux linked to monovalent cation antiport, and ATPase-dependent H(+) efflux.