CO2 permeability of the rat erythrocyte membrane and its inhibition.

We have studied the CO2 permeability of the erythrocyte membrane of the rat using a mass spectrometric method that employs 18 O-labelled CO2. The method yields, in addition, the intraerythrocytic carbonic anhydrase activity and the membrane HCO3- permeability. For normal rat erythrocytes, we find at 37 °C a CO2 permeability of 0.078 ± 0.015 cm/s, an intracellular carbonic anhydrase activity of 64,100, and a bicarbonate permeability of 2.1 × 10-3 cm/s. We studied whether the rat erythrocyte membrane possesses protein CO2 channels similar to the human red cell membrane by applying the potential CO2 channel inhibitors pCMBS, Dibac, phloretin, and DIDS. Phloretin and DIDS were able to reduce the CO2 permeability by up to 50%. Since these effects cannot be attributed to the lipid part of the membrane, we conclude that the rat erythrocyte membrane is equipped with protein CO2 channels that are responsible for at least 50% of its CO2 permeability.

Bioorganometallic derivatives of 4-hydrazino-benzenesulphonamide as carbonic anhydrase inhibitors: synthesis, characterisation and biological evaluation.

A series of bio-organometallic-hydrazones of the general formula [{(η5-C5H4)-C(R)=N-N(H)-C6H4-4-SO2NH2}]MLn(MLn = Re(CO)3, Mn(CO)3, FeCp; R=H, CH3) were prepared by reaction of formyl/acetyl organometallic precursors with 4-hydrazino-benzenesulphonamide. All compounds were characterized by conventional spectroscopic techniques (infra-red, 1H and 13C NMR, mass spectrometry and elemental analysis). Biological evaluation as carbonic anhydrase (CA, EC 4.2.1.1) inhibitors agents was carried out using four human/h) isoforms, hCA I, II, IX and XII. The cytosolic isoforms hCA I and II were effectively inhibited by almost all derivatives with inhibition constants of 1.7-22.4 nM. Similar effects were observed for the tumour-associated transmembrane isoform hCA XII (KIs of 1.9-24.4 nM). hCA IX was less sensitive to inhibition with these compounds. The presence of bio-organometallic or metallo-carbonyl moieties in the molecules of these CAIs makes them amenable for interesting pharmacologic applications, for example for compounds with CO donating properties.

Environmental co-benefits and adverse side-effects of alternative power sector decarbonization strategies.

A rapid and deep decarbonization of power supply worldwide is required to limit global warming to well below 2 °C. Beyond greenhouse gas emissions, the power sector is also responsible for numerous other environmental impacts. Here we combine scenarios from integrated assessment models with a forward-looking life-cycle assessment to explore how alternative technology choices in power sector decarbonization pathways compare in terms of non-climate environmental impacts at the system level. While all decarbonization pathways yield major environmental co-benefits, we find that the scale of co-benefits as well as profiles of adverse side-effects depend strongly on technology choice. Mitigation scenarios focusing on wind and solar power are more effective in reducing human health impacts compared to those with low renewable energy, while inducing a more pronounced shift away from fossil and toward mineral resource depletion. Conversely, non-climate ecosystem damages are highly uncertain but tend to increase, chiefly due to land requirements for bioenergy.

Tratamiento diurético del paciente con diabetes e insuficiencia cardiaca. El papel de los inhibidores de la SGLT2 y semejanzas con los inhibidores de la anhidrasa carbónica / Diuretic treatment of the patient with diabetes and heart failure. Role of SGLT2 inhibitors and similarities with carbonic anhydrase inhibitors

Los inhibidores del cotransportador sodio-glucosa tipo 2 han cambiado el concepto que se tenía de los efectos que ejercen los fármacos hipoglucemiantes sobre la insuficiencia cardiaca (IC). Es la primera vez que un grupo terapéutico modifica la evolución de la IC. Sus efectos trascienden al control glucémico, postulándose diferentes teorías para justificar estos beneficios. En este artículo analizamos la influencia que tienen sobre la IC los distintos grupos farmacológicos utilizados en el tratamiento de la diabetes mellitus tipo 2, y planteamos el posible mecanismo de acción asociado con los beneficios aportados por estos fármacos. Somos de la opinión de que este beneficio sobre la IC es secundario a su efecto diurético, en concreto a una actividad muy parecida a la de los inhibidores del dióxido de carbono. Pensamos que se trata de una teoría novedosa que explica el mecanismo de acción. No hemos encontrado en la literatura ningún artículo que desarrolle de manera tan precisa dicho mecanismo

Sodium-glucose cotransporter-2 inhibitors have changed the concept of the effects that hypoglycemic drugs have on hearth failure (HF). For the first time, a therapeutic group has modified the evolution of HF. Its effect goes beyond glycemic control, and different theories have been postulated to justify this benefit. In the article we sent, we analyze the influence of the different pharmacological groups used in type 2 diabetes mellitus on HF, and we present the theory of the mechanism of action associated with the benefit of these drugs. In our opinion, this benefit in HF is secondary to its diuretic effect, specifically an effect very similar to carbon dioxide inhibitors. We think that our theory is novel, explains the mechanism of action and we have not found in the literature any article that explains the mechanism of action in such a precise way

Non-pulsatile blood flow is associated with enhanced cerebrovascular carbon dioxide reactivity and an attenuated relationship between cerebral blood flow and regional brain oxygenation.

BACKGROUND: Systemic blood flow in patients on extracorporeal assist devices is frequently not or only minimally pulsatile. Loss of pulsatile brain perfusion, however, has been implicated in neurological complications. Furthermore, the adverse effects of absent pulsatility on the cerebral microcirculation are modulated similarly as CO2 vasoreactivity in resistance vessels. During support with an extracorporeal assist device swings in arterial carbon dioxide partial pressures (PaCO2) that determine cerebral oxygen delivery are not uncommon-especially when CO2 is eliminated by the respirator as well as via the gas exchanger of an extracorporeal membrane oxygenation machine. We, therefore, investigated whether non-pulsatile flow affects cerebrovascular CO2 reactivity (CVR) and regional brain oxygenation (rSO2). METHODS: In this prospective, single-centre case-control trial, we studied 32 patients undergoing elective cardiac surgery. Blood flow velocity in the middle cerebral artery (MCAv) as well as rSO2 was determined during step changes of PaCO2 between 30, 40, and 50 mmHg. Measurements were conducted on cardiopulmonary bypass during non-pulsatile and postoperatively under pulsatile blood flow at comparable test conditions. Corresponding changes of CVR and concomitant rSO2 alterations were determined for each flow mode. Each patient served as her own control. RESULTS: MCAv was generally lower during hypocapnia than during normocapnia and hypercapnia (p < 0.0001). However, the MCAv/PaCO2 slope during non-pulsatile flow was 14.4 cm/s/mmHg [CI 11.8-16.9] and 10.4 cm/s/mmHg [CI 7.9-13.0] after return of pulsatility (p = 0.03). During hypocapnia, non-pulsatile CVR (4.3 ± 1.7%/mmHg) was higher than pulsatile CVR (3.1 ± 1.3%/mmHg, p = 0.01). Independent of the flow mode, we observed a decline in rSO2 during hypocapnia and a corresponding rise during hypercapnia (p < 0.0001). However, the relationship between ΔrSO2 and ΔMCAv was less pronounced during non-pulsatile flow. CONCLUSIONS: Non-pulsatile perfusion is associated with enhanced cerebrovascular CVR resulting in greater relative decreases of cerebral blood flow during hypocapnia. Heterogenic microvascular perfusion may account for the attenuated ΔrSO2/ΔMCAv slope. Potential hazards related to this altered regulation of cerebral perfusion still need to be assessed. TRIAL REGISTRATION: The study was retrospectively registered on October 30, 2018, with Clinical Trial.gov (NCT03732651).

Focused Screening Identifies Evoxine as a Small Molecule That Counteracts CO2-Induced Immune Suppression.

Patients with severe lung disease may develop hypercapnia, elevation of the levels of CO2 in the lungs and blood, which is associated with increased risk of death, often from infection. To identify compounds that ameliorate the adverse effects of hypercapnia, we performed a focused screen of 8832 compounds using a CO2-responsive luciferase reporter in Drosophila S2* cells. We found that evoxine, a plant alkaloid, counteracts the CO2-induced transcriptional suppression of antimicrobial peptides in S2* cells. Strikingly, evoxine also inhibits hypercapnic suppression of interleukin-6 and the chemokine CCL2 expression in human THP-1 macrophages. Evoxine's effects are selective, since it does not prevent hypercapnic inhibition of phagocytosis by THP-1 cells or CO2-induced activation of AMPK in rat ATII pulmonary epithelial cells. The results suggest that hypercapnia suppresses innate immune gene expression by definable pathways that are evolutionarily conserved and demonstrate for the first time that specific CO2 effects can be targeted pharmacologically.

Stimuli responsive systems constructed using cucurbit[n]uril-type molecular containers.

Conspectus This Account focuses on stimuli responsive systems that function in aqueous solution using examples drawn from the work of the Isaacs group using cucurbit[n]uril (CB[n]) molecular containers as key recognition elements. Our entry into the area of stimuli responsive systems began with the preparation of glycoluril derived molecular clips that efficiently distinguish between self and nonself by H-bonds and π-π interactions even within complex mixtures and therefore undergo self-sorting. We concluded that the selectivity of a wide variety of H-bonded supramolecular assemblies was higher than previously appreciated and that self-sorting is not exceptional behavior. This lead us to examine self-sorting within the context of CB[n] host-guest chemistry in water. We discovered that CB[n] homologues (CB[7] and CB[8]) display remarkably high binding affinity (Ka up to 10(17) M(-1)) and selectivity (ΔΔG) toward their guests, which renders CB[n]s prime components for the construction of stimuli responsive host-guest systems. The CB[7]·adamantaneammonium ion complex, which is particularly privileged (Ka = 4.2 × 10(12) M(-1)), was introduced by us as a stimulus to trigger constitutional changes in multicomponent self-sorting systems. For example, we describe how the free energy associated with the formation of host-guest complexes of CB[n]-type receptors can drive conformational changes of included guests like triazene-arylene foldamers and cationic calix[4]arenes, as well as induced conformational changes (e.g., ammonium guest size dependent homotropic allostery, metal ion triggered folding, and heterochiral dimerization) of the hosts themselves. Many guests display large pKa shifts within their CB[n]-guest complexes, which we used to promote pH controlled guest swapping and thermal trans-to-cis isomerization of azobenzene derivatives. We also used the high affinity and selectivity of CB[7] toward its guests to outcompete an enzyme (bovine carbonic anhydrase) for a two-faced inhibitor, which allowed stimuli responsive regulation of enzymatic activity. These results prompted us to examine the use of CB[n]-type receptors in both in vitro and in vivo biological systems. We demonstrated that adamantaneammonium ion can be used to intracellularly sequester CB[7] from gold nanoparticles passivated with hexanediammonium ion·CB[7] complexes and thereby trigger cytotoxicity. CB[7] derivatives bearing a biotin targeting group enhance the cytotoxicity of encapsulated oxaliplatin toward L1210FR cells. Finally, acyclic CB[n]-type receptors function as solubilizing excipients for insoluble drugs for drug delivery purposes and as a broad spectrum reversal agent for the neuromuscular blocking agents rocuronium, vecuronium, and cis-atracurium in rats. The work highlights the great potential for integration of CB[n]-type receptors with biological systems.

A unified electrocatalytic description of the action of inhibitors of nickel carbon monoxide dehydrogenase.

Several small molecules and ions, notably carbon monoxide, cyanide, cyanate, and hydrogen sulfide, are potent inhibitors of Ni-containing carbon monoxide dehydrogenases (Ni-CODH) that catalyze very rapid, efficient redox interconversions of CO(2) and CO. Protein film electrochemistry, which probes the dependence of steady-state catalytic rate over a wide potential range, reveals how these inhibitors target particular oxidation levels of Ni-CODH relating to intermediates (C(ox), C(red1), and C(red2)) that have been established for the active site. The following properties are thus established: (1) CO suppresses CO(2) reduction (CO is a product inhibitor), but its binding affinity decreases as the potential becomes more negative. (2) Cyanide totally inhibits CO oxidation, but its effect on CO(2) reduction is limited to a narrow potential region (between -0.5 and -0.6 V), below which CO(2) reduction activity is restored. (3) Cyanate is a strong inhibitor of CO(2) reduction but inhibits CO oxidation only within a narrow potential range just above the CO(2)/CO thermodynamic potential--EPR spectra confirm that cyanate binds selectively to C(red2). (4) Hydrogen sulfide (H(2)S/HS(-)) inhibits CO oxidation but not CO(2) reduction--the complex on/off characteristics are consistent with it binding at the same oxidation level as C(ox) and forming a modified version of this inactive state rather than reacting directly with C(red1). The results provide a new perspective on the properties of different catalytic intermediates of Ni-CODH--uniting and clarifying many previous investigations.

Inner ear insult suppresses the respiratory response to carbon dioxide.

Compensated respiratory acidosis has been observed in a significant number of patients with active vestibular disease. We therefore hypothesized that the inner ear may play an unrecognized integral role in respiratory control. To test this premise, we investigated whether mice with induced inner ear injury demonstrated any alteration in their respiratory response to inhaled carbon dioxide (CO(2)). Experimental mice and control mice were included in two separate experiments. Intra-tympanic gentamycin injections were administered to induce inner ear damage in experimental animals. Hearing loss and vestibular dysfunction were tested 1-week after injections to confirm presence of inner ear insult, following which the animal's respiratory response to inhalation of 8% CO(2) was examined. Mice with inner ear injury (n=60) displayed a significantly diminished hypercapnic ventilatory response (HCVR). This contrasted with the normal HCVR seen in control mice that had not undergone tympanic injections (n=30), controls that received tympanic injections with saline (n=5), and controls that had gentamicin administered systemically (n=5). In response to inspired CO(2), the mean respiratory frequency of control mice increased by an average of 50% over their baseline values for both parts of the experiment. In contrast, the ear-damaged experimental group mean values increased by only three breaths per minute (bpm) (2%) in the first experiment and by 28 bpm (11%) in the second experiment. Inner ear damage significantly reduces the respiratory response to CO(2) inhalation. In addition to the established role of the inner ear organ in hearing and balance, this alludes to an unidentified function of the inner ear and its interconnecting neuronal pathways in respiratory regulation. This finding may offer valuable new clues for disease states with abnormal respiratory control where inner ear dysfunction may be present.

An analytical model of non-photorespiratory CO2release in the light and dark in leaves of C3species based on stoichiometric flux balance.

Leaf respiration continues in the light but at a reduced rate. This inhibition is highly variable, and the mechanisms are poorly known, partly due to the lack of a formal model that can generate testable hypotheses. We derived an analytical model for non-photorespiratory CO2 release by solving steady-state supply/demand equations for ATP, NADH and NADPH, coupled to a widely used photosynthesis model. We used this model to evaluate causes for suppression of respiration by light. The model agrees with many observations, including highly variable suppression at saturating light, greater suppression in mature leaves, reduced assimilatory quotient (ratio of net CO2 and O2 exchange) concurrent with nitrate reduction and a Kok effect (discrete change in quantum yield at low light). The model predicts engagement of non-phosphorylating pathways at moderate to high light, or concurrent with processes that yield ATP and NADH, such as fatty acid or terpenoid synthesis. Suppression of respiration is governed largely by photosynthetic adenylate balance, although photorespiratory NADH may contribute at sub-saturating light. Key questions include the precise diel variation of anabolism and the ATP : 2e⁻ ratio for photophosphorylation. Our model can focus experimental research and is a step towards a fully process-based model of CO2 exchange.

Helium-oxygen reduces the production of carbon dioxide during weaning from mechanical ventilation.

BACKGROUND: Prolonged weaning from mechanical ventilation has a major impact on ICU bed occupancy and patient outcome, and has significant cost implications.There is evidence in patients around the period of extubation that helium-oxygen leads to a reduction in the work of breathing. Therefore breathing helium-oxygen during weaning may be a useful adjunct to facilitate weaning. We hypothesised that breathing helium-oxygen would reduce carbon dioxide production during the weaning phase of mechanical ventilation. MATERIALS/PATIENTS AND METHODS: We performed a prospective randomised controlled single blinded cross-over trial on 19 adult intensive care patients without significant airways disease who fulfilled criteria for weaning with CPAP. Patients were randomised to helium-oxygen and air-oxygen delivered during a 2 hour period of CPAP ventilation. Carbon dioxide production (VCO2) was measured using a near patient main stream infrared carbon dioxide sensor and fixed orifice pneumotachograph. RESULTS: Compared to air-oxygen, helium-oxygen significantly decreased VCO2 production at the end of the 2 hour period of CPAP ventilation; there was a mean difference in CO2 production of 48.9 ml/min (95% CI 18.7-79.2 p = 0.003) between the groups. There were no significant differences in other respiratory and haemodynamic parameters. CONCLUSION: This study shows that breathing a helium-oxygen mixture during weaning reduces carbon dioxide production. This physiological study supports the need for a clinical trial of helium-oxygen mixture during the weaning phase of mechanical ventilation with duration of weaning as the primary outcome. TRIAL REGISTRATION: ISRCTN56470948.

Antagonistic interaction between oxygenation-linked lactate and CO2 binding to human hemoglobin.

Oxygen binding to hemoglobin (Hb) depends on allosteric effectors (CO(2), lactate and protons) that may increase drastically in concentration during exercise. The effectors share common binding sites on the Hb molecules, predicting mutual interaction in their effects on Hb (de)oxygenation. We analysed the effects of lactate and CO(2), separately and in combination, on O(2) binding of purified human Hb at 37 degrees C and physiological pH and chloride values. We demonstrate pH-dependent, inhibitory interactions between lactate binding and CO(2) binding (carbamate formation); at pH 7.4, physiological CO(2) tension ( approximately 43 mm Hg) reduced lactate binding more markedly ( approximately 75%), than lactate (50 mM) inhibited carbamate formation ( approximately 25%). In contrast to previous studies on blood and Hb solutions, we moreover find that added lactate neither 'reverses' oxylabile carbamate formation (resulting in lower carbamate levels in deoxyHb than in oxyHb) nor exerts greater allosteric effects on Hb-O(2) affinity than equal increases in chloride ion concentrations.

Effects of acetazolamide and 4-aminopyridine on CO2-induced slowly adapting pulmonary stretch receptor inhibition in rats.

Inhibitory responses of slowly adapting pulmonary stretch receptor (SAR) activity to CO(2) inhalation (maximal tracheal CO(2) concentration ranging from 9.5 to 12.5%) for approximately 60 s were examined before and after administration of acetazolamide (a carbonic anhydrase inhibitor) or 4-aminopyridine (4-AP, a K(+) channel blocker). The experiments were performed in 35 anesthetized, artificially ventilated rats after unilateral vagotomy. Sixty-eight of eighty-four SARs were inhibited by CO(2) inhalation. The SAR inhibition was attenuated by pretreatment with either acetazolamide (20 mg/kg, n = 10) or 4-AP (0.7 and 2.0 mg/kg, n = 10). In other series of experiments, stainings to show the existence of carbonic anhydrase (CA) enzymatic reaction were not found in the smooth muscle of either extrapulmonary or intrapulmonary bronchi. Protein gene product 9.5 (PGP 9.5)-immunoreactive SAR terminals to form leaflike extensions were found in the bronchioles at different diameters and were smooth-muscle-related receptors. But in the same sections, CA isozyme II-like (erythrocyte CA) immunoreactive SAR terminals were not identified. These results suggest that CO(2)-induced inhibition of SARs may be involved in the CA-dependent CO(2) hydration in addition to the activation of 4-AP sensitive K(+) currents.

ANG II reduces net acid secretion in rat outer medullary collecting duct.

In rat outer medullary collecting duct (OMCD), the mechanism(s) and regulation of H+ secretion are not understood fully. The effect of changes in acid-base balance and the renin-angiotensin system on net H+ secretion was explored. Rats received NaCl, NaHCO3, NH4Cl, or nothing in their drinking water for 7 days. Total ammonia and total CO2 (JtCO2) fluxes were measured in OMCD tubules perfused in vitro from rats in each treatment group. JtCO2 was reduced in tubules from rats drinking NH4Cl relative to those drinking NaHCO3. Because NH4Cl intake increases plasma renin and aldosterone, we asked if upregulation of the renin-angiotensin system reduces net H+ secretion. Deoxycorticosterone pivalate administered in vivo did not affect JtCO2. However, ANG II given in vivo at 0.1 ng/min reduced JtCO2 by 35%. To determine if ANG II has a direct effect on acid secretion, JtCO2 was measured with ANG II applied in vitro. ANG II (10-8 M) present in the bath solution reduced JtCO2 by 35%. This ANG II effect was not observed in the presence of the AT1 receptor blocker candesartan. In conclusion, in rat OMCD, JtCO2 is paradoxically reduced with NH4Cl ingestion. Increased circulating ANG II, as occurs during metabolic acidosis, reduces JtCO2.

CO2 response for expression of ribulose-1,5-bisphosphate carboxylase/oxygenase genes is inhibited by AT-rich decoy in the cyanobacterium.

The CO(2)-regulatory function of the AT-rich element in the promoter for ribulose-1,5-bisphosphate carboxylase/oxygenase (rbc) genes in the cyanobacterium Synechococcus sp. PCC7002 was analyzed using the transcription factor decoy approach. Double-stranded phosphorothioate AT-rich oligonucleotides with high affinity for a sequence-specific DNA-binding protein were successfully introduced into cyanobacterial cells in culture without any transfection reagent. The AT-rich decoy oligonucleotides interfered with CO(2) regulation of rbc expression by blocking the binding of the sequence-specific DNA-binding protein, indicating that the AT-rich element plays a critical role in CO(2) regulation for rbc genes. The decoy oligonucleotide approach to cyanobacteria provides a simple and excellent tool for investigating transcriptional regulation in vivo.

Estrogen attenuates cell death induced by carboxy-terminal fragment of amyloid precursor protein in PC12 through a receptor-dependent pathway.

In the present study, we investigated effects of estrogen on cell death induced by carboxy-terminal fragment of amyloid precursor protein (CT), a candidate causative substance in the pathogenesis of Alzheimer's disease. 17 beta-Estradiol attenuated CT-induced cell death in PC12 cells, whereas 17 alpha-estradiol, nonestrogenic stereoisomer, did not exert any significant protective effect on CT-induced cell death. These results suggest that protective effects of estrogen may be mediated by estrogen receptor (ER) in PC12 cells. To confirm the results, we determined the effects of tamoxifen, an estrogen receptor antagonist. Tamoxifen blocked the protective effects of 17 beta-estradiol, although it did not affect those of 17 alpha-estradiol. Overall, it might be thought that the protective effect of estradiol on CT-induced cell death is achieved by hormonal properties mediated through the estrogen receptor rather than the structural properties as a reducing agent.

Homocysteine and hypomethylation. A novel link to vascular disease.

A mild elevation in serum homocysteine levels is an independent risk factor for arteriosclerosis and venous thrombosis. Despite the clinical significance of homocysteine, however, the molecular mechanisms of homocysteine-induced arteriosclerosis have not been completely elucidated. This lack of understanding is due in large part to the excessively high concentrations of homocysteine (greater than 1 mM) used in experiments. Many of homocysteine's effects have been attributed to its prooxidant activity, which is implicated as the mechanism through which it inhibits production of endothelium-derived relaxing factor and activates quiescent vascular smooth muscle cells. We have found that homocysteine at 10 to 50 microM (but not cysteine) inhibits progression of the vascular endothelial cell cycle at or before the G1-S junction. This inhibition appears to be mediated by decreases in the carboxyl methylation, membrane association, and activity of p21ras--a major G1 regulator. Homocysteine may play an important role in promoting arteriosclerosis by inducing endothelial dysfunction, by inhibiting endothelial cell regeneration, and by directly activating quiescent vascular smooth muscle cells.

Suppression of CO2-induced relaxation of bovine retinal pericytes by angiotensin II.

PURPOSE: To determine whether angiotensin II (Ang II), a vasoconstrictive peptide, changes the relaxation effect of elevated partial pressure of carbon dioxide (PCO2) on pericytes. METHODS: The contractile tone of cultured bovine retinal pericytes was measured when the ambient PCO2 was elevated in the absence or the presence of Ang II. All experiments were performed in the bicarbonate-buffered solution at 37 degrees C. RESULTS: Ang II (10(-6) M) by itself did not increase the baseline tone of the pericytes. Raising the PCO2 from 5% to 20% acidified the solution (pH dropped 0.51 +/- 0.02 U) and caused a sustained and statistically significant 22.9% +/- 4.6% relaxation of pericytes within 5 minutes (n = 8). In the presence of Ang II (10(-6) M), the maximum relaxation induced by 20% PCO2 was only 12.6% +/- 4.5% (n = 6) at 3 minutes, and the relaxation was not sustained. The effect of Ang II was statistically significant. Pretreatment with the competitive Ang II receptor antagonist saralasin (10(-6) M) for 10 minutes completely abolished the effect of Ang II (10(-6) M) on the response of pericytes to 20% PCO2. Saralasin by itself had no effect. CONCLUSIONS: Ang II attenuated the relaxing response of pericytes to elevated PCO2 through saralasin-sensitive Ang II receptors. Results suggest that some vasoactive agents, such as Ang II, could affect the pericyte responses to metabolic needs as signaled by local PCO2. This experimental design may permit further investigation of the altered physiology of local blood flow regulation.

Thiolmethyltransferase activity in the human colonic mucosa: implications for ulcerative colitis.

Ulcerative colitis is associated with a selective reduction of n-butyrate oxidation by the colonic epithelial cells although the reason for this has been unclear. Colonic epithelial cell n-butyrate oxidation can be inhibited in vitro by incubation with sulphide but the role of mucosal detoxification of sulphide in the metabolic welfare of the colonic mucosa has not been examined. This study aimed to assess the role mucosal detoxification of sulphide by thiolmethyltransferase (TMT)-mediated methylation may play in protecting the healthy colonic mucosa from the adverse effects of luminal sulphide. Colonic epithelial cell suspensions from healthy human proximal (n = 9) and distal colon (n = 10) were incubated in the presence of 14C-labelled n-butyrate (5 mmol/L) alone, butyrate plus sodium hydrogen sulphide (NaHS) (1.5 mmol/L), or butyrate plus NaHS plus S-adenosyl-methionine 1,4 butane disulphonate (SAMe) (5 mmol/L). Study end points were metabolic performance (14CO2 production) and mucosal TMT activity. Incubation with NaHS induced a significant inhibition of 14CO2 production compared with control incubations (P < 0.001) which was similar for proximal and distal colonic cell suspensions. S-adenosyl-methionine 1,4 butane disulphonate reversed this effect completely in proximal but not in distal cell incubations, suggesting a greater susceptibility of the distal colon to the sulphide effect. Although median whole mucosal TMT values did not differ between proximal and distal colonic mucosa, a non-normal distribution of distal TMT values was observed. However, neither the degree of sulphide inhibition of control 14CO2 production nor the degree to which SAMe reversed this inhibition correlated with whole mucosal TMT activity. The study concluded that regional variation exists in TMT activity in the human colon but whilst methylation appears to protect colonic epithelial cells against sulphide-induced inhibition of n-butyrate oxidation, this cannot be directly correlated with mucosal TMT activity.

Effects of morphine and physostigmine on the ventilatory response to carbon dioxide.

BACKGROUND: It has been reported that physostigmine antagonizes morphine-induced respiratory depression, but it is not known whether this is due to a central chemoreceptor effect, an effect on the peripheral chemoreflex loop, or both. We therefore assessed the effect of morphine and physostigmine on the normoxic hypercapnic ventilatory response mediated by the central and peripheral chemoreceptors in ten alpha-chloralose-urethan-anesthetized cats. METHODS: The breath-by-breath ventilatory responses to stepwise changes in end-tidal CO2 tension were determined before (control), after administration of morphine hydrochloride (0.15 mg.kg-1) and during intravenous infusion of physostigmine salicylate (bolus of 0.05 mg.kg-1 followed by 0.025 mg.kg-1.h-1). Each response was separated into a central and a peripheral chemoreflex characterized by CO2 sensitivity (Sc and Sp), time constant, time delay, and apneic threshold (a single off-set B). RESULTS: Morphine increased B and decreased Sc and Sp (P < 0.01), but not the ratio Sp/Sc. Subsequent infusion of physostigmine decreased B (P < 0.01), without further change of Sp and Sc. Premedication with physostigmine decreased B, Sp and Sc (P < 0.01) vs. control, but not Sp/Sc. Subsequent administration of morphine decreased Sp and Sc further but increased B (P < 0.01), while Sp/Sc remained constant. CONCLUSIONS: Because morphine diminishes the Sc and Sp of the chemoreflex loop to the same extent this depressant effect is presumably due to an action on the respiratory integrating centers rather than on the peripheral and central chemoreceptors as such and is not antagonized by physostigmine. We argue that the increase in B may be due to changes in the amount of acetylcholine available in the brain and can be antagonized by physostigmine.