pH-dependent fusion of synaptosomal membrane studied by fluorescence quenching method

We have found that both the synaptic vesicles (SV) and synaptic plasma membrane vesicles (SPM) have an activity to fuse with phosphatidylcoline/phosphatidylserine liposomes in a pH-dependent manner. The activity increases with decreases in extravesicular pH. At a pH lower than 4.0, the activity is almost steady at its maximum value, and there was a rapid drop around pH 5.5. The pH-dependent fusion was inhibited by proteolysis with trypsin; hence, at least in part, some membrane proteins play an important role in these pH-dependent fusion processes. To find specific markers, we screened various protein modifiers and found that anion channel blockers, stilbene derivatives (DIDS and SITS) and glibenclamide, affected the fusion process. DIDS and SITS decreased the fusion activity with an IC50 of 180 and 300 microM, respectively, whereas glibenclamide, on the contrary, increased it. From the results of an autoradiogram using 3H-tagged DIDS, a 30 kDa DIDS-binding protein was identified in the synaptic plasma membrane, which is possible to be responsible for the pH-dependent fusion.

Studies on the structures and antigenic properties of rabies virus glycoprotein analogues produced in yeast cells

We investigated two forms (designated as yGI and yGII) of rabies virus glycoprotein (G) analogues produced in the G cDNA-transfected yeast cells. Molecular weights of yGI and yGII were estimated as 66 and 56 kDa, respectively, according to their relative mobility in SDS-PAGE. Although being produced in large amounts, yGI was present mostly in insoluble forms and hardly extractable with non-ionic detergents. The yGI reacted with polyclonal anti-G antibodies, but did not react with our conformational epitope-specific anti-G monoclonal antibodies (G-MAbs). No protective immunity was induced by yGI in guinea pigs nor in mice. On the other hand, yGII was Triton-soluble, but was only small in amount (at most 1% of total G proteins) and was shown to lack the cytoplasmic domain. The yGII, however, reacted with the G-MAbs and induced protective immunity in guinea pigs as well. When the G-cDNA was expressed in animal cells in culture, a single form (about 66 kDa) of G protein was produced, which displayed similar behaviors as seen in its reactivity with the MAbs and intracellular distribution as seen in the virus-infected cells. These results suggest that most G protein molecules were not processed normally in yeast cells, resulting in abnormal folding and multimer formation, while only a small fraction were occasionally folded normally to have conformational epitopes but were mostly deprived of the C-terminal portion.

A low concentration of nitrous oxide reduces dyspnoea produced by a combination of hypercapnia and severe elastic load

We have measured how a low concentration of nitrous oxide affected respiratory sensation and ventilation. Severe dyspnoea was induced in nine normal subjects by a combination of hypercapnia and inspiratory elastic load (50 cm H2O litre-1). Subjects were asked to rate their sensation of respiratory discomfort using a visual analogue scale (VAS) while breathing either 20% nitrous oxide or 20% nitrogen gas mixture. We compared the effects of each gas mixture on respiratory sensation and ventilation using steady-state values of ventilatory variables and VAS scores obtained before, during and after inhalation of each gas mixture. Inhalation of 20% nitrous oxide reduced the sensation of respiratory discomfort from a median VAS score of 6.5 (range 5.0-8.1) before inhalation to 3.6 (2.4-5.9) during inhalation (P < 0.05). There was no significant change in minute ventilation but tidal volume increased during inhalation of 20% nitrogen did not alter VAS scores or ventilatory variables. We found that a low concentration of nitrous oxide greatly alleviated the intensity of dyspnoea without changing respiratory load compensation.

Effects of negative pressure assisted ventilation on dyspnoeic sensation and breathing pattern

Although negative pressure assisted ventilation with an assist-control mode may have a potential therapeutic role in the treatment of severe dyspnoea, the effects of negative pressure assisted ventilation with the assist-control mode on dyspnoea and breathing patterns have not been examined. We examined the effects of negative pressure assisted ventilation with the assist-control mode on dyspnoea and breathing patterns produced by a combination of resistive loading and hypercapnia in nine healthy subjects breathing spontaneously. Subjects were asked to rate their sensation of respiratory discomfort using a visual analogue scale. Negative pressure assisted ventilation caused a significant reduction in sensation of respiratory discomfort from a visual analogue scale score of 74 (55-91) (median (range)) before negative pressure assisted ventilation to 34 (15-53) during negative pressure assisted ventilation (p<0.01). During negative pressure assisted ventilation, there were significant changes in breathing patterns characterized by an increase in tidal volume and a decrease in respiratory frequency, while neither minute ventilation nor end-tidal carbon dioxide tension changed. Our results indicate that negative pressure assisted ventilation with the assist-control mode is effective in relief of dyspnoea and that negative pressure assisted ventilation influences the control of breathing to minimize respiratory discomfort.

A novel insulin sensitizer acts as a coligand for peroxisome proliferator-activated receptor-alpha (PPAR-alpha) and PPAR-gamma: effect of PPAR-alpha activation on abnormal lipid metabolism in liver of Zucker fatty rats

We investigated the biological activity of a novel thiazolidinedione (TZD) derivative, KRP-297, and the molecular basis of this activity. When administered to obese Zucker fatty rats (obese rats) at 10 mg/kg for 2 weeks, KRP-297, unlike BRL-49,653, restored reduced lipid oxidation, that is, CO2 and ketone body production from [14C]palmitic acid, in the liver by 39% (P < 0.05) and 57% (P < 0.01), respectively. KRP-297 was also significantly more effective than BRL-49,653 in the inhibition of enhanced lipogenesis and triglyceride accumulation in the liver. To understand the molecular basis of the biological effects of KRP-297, we examined the effect on peroxisome proliferator-activated receptor (PPAR) isoforms, which may play key roles in lipid metabolism. Unlike classical TZD derivatives, KRP-297 activated both PPAR-alpha and PPAR-gamma, with median effective concentrations of 1.0 and 0.8 micromol/l, respectively. Moreover, radiolabeled [3H]KRP-297 bound directly to PPAR-alpha and PPAR-gamma with dissociation constants of 228 and 326 nmol/l, respectively. Concomitantly, KRP-297, but not BRL-49,653, increased the mRNA and the activity (1.5-fold [P < 0.01] and 1.8-fold [P < 0.05], respectively) of acyl-CoA oxidase, which has been reported to be regulated by PPAR-alpha, in the liver. By contrast, KRP-297 (P < 0.05) was less potent than BRL-49,653 (P < 0.01) in inducing the PPAR-gamma-regulated aP2 gene mRNA expression in the adipose tissues. These results suggest that PPAR-alpha agonism has a protective effect against abnormal lipid metabolism in liver of obese rats.

New method to measure telomerase activity by transcription-mediated amplification and hybridization protection assay

Telomerase is a ribonucleoprotein complex that uses RNA as a template for the addition of telomeric repeats. The development of the telomeric repeat amplification protocol (TRAP), a sensitive PCR-based assay, has facilitated the detection of telomerase activity in small tissue and tumor samples. Telomerase activity is expected to be a new diagnostic and prognostic marker of human cancer. In this study, we applied a non-PCR-based transcription-mediated amplification (TMA) and hybridization protection assay (HPA) to the measurement of telomerase activity by modification of both primers in TMA. We demonstrated that the modified TMA can detect and measure telomerase activity. TMA/HPA is as sensitive and reproducible as conventional TRAP, but is both faster and easier to perform. Furthermore, we found that TMA/HPA was influenced minimally by TRAP inhibitors that may come from clinical samples. TMA/HPA, which is easy, rapid, and applicable to a high-throughput format, should be clinically useful for the detection and monitoring of telomerase activity.

Expression of telomerase catalytic component, telomerase reverse transcriptase, in human gastric carcinomas

Telomerase activity is believed to be crucial for cellular immortality, which is considered to participate in the development of a majority of human cancers. Human telomerase reverse transcriptase (TERT) has recently been identified as a catalytic subunit of telomerase. We examined the expression of TERT and other telomerase components such as human telomerase RNA component (hTR, encoded by TERC) and human telomerase-associated protein (TEP1) by reverse transcription-polymerase chain reaction in human gastric carcinomas and non-neoplastic mucosa, in addition to measuring the telomerase activity. Of 20 gastric carcinomas examined, 18 (90%) and 18 (90%) showed increased expression of TERT and higher telomerase activity in comparison with corresponding non-neoplastic mucosa, respectively. Increased expression of hTR/TERC was also observed in 15 (75%) of the gastric carcinomas. Immunohistochemically, strong expression of TERT protein was detected in the nuclei of the tumor cells of all carcinoma tissues, while the expression of TERT in non-neoplastic mucosal cells as well as stromal elements (except lymphocytes) was weak or negative. These findings suggest that increased TERT expression associated with telomerase activity may serve as a novel marker for the diagnosis of stomach cancer.

In situ mRNA hybridization technique for analysis of human telomerase RNA in gastric precancerous and cancerous lesions

Telomerase, the ribonucleoprotein enzyme that elongates telomerase, is repressed in normal somatic cells but is reactivated during tumor progression. The purpose of this study was to investigate the localization of human telomerase RNA (hTR) expression in human gastric precancerous and cancerous lesions by using in situ mRNA hybridization (ISH) with avidin-biotin staining. We also examined telomerase activity in these lesions by using hybridization protection assay connected with a telomeric repeat amplification protocol (TRAP/HPA). Analyzed tissue samples were as follows; 132 cases of chronic atrophic gastritis without intestinal metaplasia, 115 incomplete-type intestinal metaplasias, 40 complete-type intestinal metaplasias, 23 hyperplastic polyps, 23 tubular adenomas and 26 adenocarcinomas. In ISH analysis, high levels of hTR expression were observed preferentially in the nuclei at the single-cell level. hTR-expressing cells in carcinomas and adenomas were significantly more frequent than those of the other lesions (P < 0.001). The expression pattern of hTR in carcinoma and adenoma tissues was heterogeneous and similar intratumor heterogeneity was detected in Ki-67 immunoreactivity. Infiltrating lymphocytes in tissue also exhibited high levels of hTR expression. In TRAP/HPA analysis, carcinomas had significantly more frequent positivity for telomerase activity and a higher level of telomerase activity than the other lesions (P < 0.05). However, the amount of telomerase activity did not parallel the expression level of hTR. Our data suggest that hTR expression increases in the early stages of stomach carcinogenesis and that sufficient synthesis of hTR is a prerequisite for telomerase reactivation in tumorigenesis.

Reciprocal effects of dietary sesamin on ketogenesis and triacylglycerol secretion by the rat liver

The effects of dietary sesamin (a mixture of sesamin and episesamin, 1:1, w/w) on ketone body production and lipid secretion were studied in isolated perfused liver from rats given sesamin. Feeding sesamin at the dietary level of 0.2% from 14 to 16 d resulted in an enlargement of liver weight. Ketone body production was significantly elevated in the livers perfused with oleic acid in comparison with those perfused without an exogenous-free fatty acid, and sesamin feeding caused a stimulation of ketone body production, especially when exogenous oleic acid was provided. On the other hand, the ratio of beta-hydroxybutyrate to acetoacetate, an index of mitochondrial redox potential, tended to increase in the livers perfused with oleic acid compared with those without fatty acid, thought it was consistently lowered by dietary sesamin. The cumulative secretion of triacylglycerol, but not of cholesterol, by the livers from sesamin-fed rats was decreased markedly, especially when exogenous oleic acid was provided, suggesting an inverse relationship between the rates of ketogenesis and triacylglycerol secretion. These results suggest that dietary sesamin exerts its hypotriglyceridemic effect at least in part through an enhanced metabolism of exogenous-free fatty acid to oxidation at the expense of esterification in rat liver.

Expressional changes in alternative splicing affecting genes during cell passage of human diploid fibroblasts

Normal human diploid cells have a limited proliferative lifespan in in vitro cultures. Changes in gene expression have been examined for understanding control mechanisms of limited proliferative lifespan. and enhanced expression of growth suppressing genes such as p21 was reported in late-passaged cells. We screened genes which were expressed preferentially in mid-passaged cells by the differential plaque screening of the subtracted cDNA libraries prepared from young, life-extended, and immortalized SV40-transformed human fibroblasts. Among isolated clones, ASF/SF2, which was known to affect alternative splicing, was expressed in normal fibroblasts with a peak at mid-passage. Relative expression levels of SC35 and hnRNPA1, which are also known to affect alternative splicing, was also highest at mid-passage. Changes in alternative splicing at mid-passage, if it occurred, may play a crucial role in the process of cellular senescence.

[Standardization of hemopoietic colony assay reagents]

Several Japanese Red Cross blood centers have begun cooperating with hospitals in peripheral blood stem cell transplantation research. However, most have not yet standardized their techniques or reagents for that purpose yet. Consequently, wide variations are often observed in data from different blood centers, especially for hemopoietic colony assays. We compared our colony assay reagent set with those in three commercial colony assay kits. The best results were obtained with the kit from a manufacturer referred to here as company A. Although our reagent set obtained lower colony values, the CFU-GM, BFU-E, and total colony values correlated well with those obtained using company A's kit (r = 0.74, 0.80, and 0.97, respectively). Company A's kit gave reproducible results even with the use of different lots, and includes reagents that can be stored for up to two years at -20 degrees C. These features highlighted its advantages as a standard reagent set.

Effect of emeriamine, an inhibitor of fatty acid oxidation, on metabolic fate of a geometrical isomer of linoleic acid in perfused rat liver

To estimate the relative significance of exogenous vs. endogenous fatty acids in increasing hepatic triacylglycerol secretion following an inhibition of fatty acid oxidation by emeriamine, livers from 2-d-fasting rats were perfused with or without an inhibitor in the presence of a geometrical isomer of linoleate (linolelaidic acid, trans,trans-9,12-octadecadienoic acid). Emeriamine added to the perfusion medium at 2 h of the recirculating perfusion period caused immediate and complete cessation of ketone body production while it increased triacylglycerol and cholesterol secretion by the liver without affecting uptake of exogenous linolelaidic acid. The increase in the triacylglycerol secretion by emeriamine was accompanied by a marked increase in the proportion of linolelaidic acid in this lipid molecule in the perfusate and in the liver. The calculated amounts of exogenous linolelaidate, compared with those of endogenous fatty acids in the secretory triacylglycerol, suggested that the former compared with the latter contributes more to the drug-mediated increase in triacylglycerol secretion. This drug caused a marked reduction of mitochondrial carnitine palmitoyltransferase activity in perfused liver. These results suggest that a blockade of fatty acid oxidation by emeriamine, through an inhibition of carnitine palmitoyltransferase, diverts predominantly the exogenous free fatty acids from oxidation to the esterification pathway and subsequently stimulates the synthesis and secretion of triacylglycerol-rich lipoproteins.

Negative-strand HCV RNA was not detected in bone marrow cells of patients with HCV infection

To determine whether hepatitis C virus (HCV) replicates in bone marrow, we investigated positive- and negative-strand HCV RNA in bone marrow cells and fluids, and sera from patients with HCV infection. The study population consisted of 15 patients positive for antibodies to HCV (anti-HCV). Positive- and negative-strands HCV RNA were detected using highly strand-specific rTth reverse transcription-polymerase chain reaction (rTth RT-PCR) followed by Southern blotting analysis. Positive-strand HCV RNA was detected in 12 (80%) serum samples, in 13 (86.7%) bone marrow fluid specimens, and in 6 (40.0%) bone marrow cell samples. Negative-strand HCV RNA was detected in 9 (60.0%) serum samples, 11 (91.7%) fluid specimens, while it was not detected in bone marrow cells. The absence of negative-strand HCV RNA in bone marrow cells suggested that HCV does not replicate in these cells. Negative-strand HCV RNA detected in serum and bone marrow fluid samples may have been due to contamination with circulating HCV RNA from hepatocytes.

Comparative effects of alpha- and gamma-linolenic acids on rat liver fatty acid oxidation

It has been reported that both n-3 and n-6 octadecatrienoic acids can increase hepatic fatty acid oxidation activity. It remains unclear, however, whether different enzymes in fatty acid oxidation show a similar response to n-3 and n-6 octadecatrienoic acids. The activity of hepatic fatty acid oxidation enzymes in rats fed an oil mixture rich in alpha-linolenic acid (18:3n-3) and borage oil rich in gamma-linolenic acid (18:3n-6) was therefore compared to that in rats fed an oil mixture rich in linoleic acid (18:2n-6) and a saturated fat (palm oil) in this study. Linseed oil served as the source of 18:3n-3 for the oil mixture rich in this octadecatrienoic acid and contained 30.6% 18:3n-3 but not 18:3n-6. Borage oil contained 25.7% 18:3n-6 and 4.5% 18:3n-3. Groups of seven rats each were fed diets containing 15% various fats for 15 d. The oxidation rate of palmitoyl-CoA in the peroxisomes was higher in rats fed a fat mixture rich in 18:3n-3 (3.03 nmol/min/mg protein) and borage oil (2.89 nmol/min/mg protein) than in rats fed palm oil (2.08 nmol/min/mg protein) and a fat mixture rich in 18:2n-6 (2.15 nmol/min/mg protein). The mitochondrial palmitoyl-CoA oxidation rate was highest in rats fed a fat mixture rich in 18:3n-3 (1.93 nmol/min/mg protein), but no significant differences in this parameter were seen among the other groups (1.25-1.46 nmol/min/mg protein). Compared to palm oil and fat mixtures rich in 18:2n-6, a fat mixture rich in 18:3n-3 and borage oil significantly increased the hepatic activity of carnitine palmitoyltransferase and acyl-CoA oxidase. Compared to palm oil and a fat mixture rich in 18:2n-6, a fat mixture rich in 18:3n-3, but not fats rich in 18:3n-6, significantly decreased 3-hydroxyacyl-CoA dehydrogenase activity. Compared to palm oil and a fat mixture rich in 18:2n-6, borage oil profoundly decreased mitochondrial acyl-CoA dehydrogenase activity, but a fat mixture rich in 18:3n-3 increased it. 2,4-Dienoyl-CoA reductase activity was significantly lower in rats fed palm oil than in other groups. Compared to other fats, borage oil significantly increased delt3,delta2-enoyl-CoA isomerase activity. Activity was also significantly higher in rats fed 18:2n-6 oil than in those fed palm oil. It was confirmed that both dietary 18:3n-6 and 18:3n-3 increased fatty acid oxidation activity in the liver. These two dietary octadecatrienoic acids differ considerably, however, in how they affect individual fatty acid oxidation enzymes.

Extra-chromosomal telomere repeat DNA in telomerase-negative immortalized cell lines

We found novel extra-chromosomal telomere repeat (ECTR) DNAs in telomerase-negative immortalized KMST-6 cells, by staining these cells with a (TTAGGG)n probe using both cycling oligonucleotide-primed in situ synthesis and by fluorescence in situ hybridization. Relatively small amounts of ECTR DNAs were also observed in telomerase-negative VA13 and SUSM-1 cells, but not observed in telomerase-positive immortalized HeLa cells. The ECTR DNAs existed mainly in the nucleoplasm with a small amount in the cytoplasm. The nucleoplasm ECTR DNAs were co-stained with an antibody directed to the telomeric-repeat binding factor 1 (TRF1), suggesting that they exist as a complex with TRF1. In consistent with these cytological studies, Southern blot analysis showed the existence of small telomere repeat DNAs. The ECTR DNA may provide an insight into the elucidation of the mechanisms responsible for the maintenance of telomeres in telomerase-negative immortalized cells.

A hVti1 homologue: its expression depends on population doubling levels in both normal and SV40-transformed human fibroblasts

A cDNA clone was isolated by differential colony hybridization from a cDNA library prepared from life-extended SV40-transformed human fibroblasts. The clone, tentatively named N-10, was 1272 bp in length coding for 232 amino acids. Northern analysis revealed that the expression level of N-10 was increased in normal senescent and life-extended SV40-transformed fibroblasts than in their young counterparts but was not enhanced by growth arrest. The protein fused to GFP (green fluorescent protein) localized in cytoplasmic granule. Enforced expression of N-10 resulted in premature senescence in young fibroblasts. The deduced amino acid sequence of N-10 was identical to the recently reported hVti1 gene except in one amino acid: Asp24(GAC) was ours and Asn24 (AAC) was reported. Additional base differences were found, so we referred to our sequence as the hVti1 homologue. As hVti1 protein was suggested to be involved in the vesicle transport process, the homologue may be concerned with increased secretion of extracellular matrix and various cytokines associated with cellular senescence.

RD6-2198, a novel betain-type fluoroalkylated oligomer, inhibits the replications of human immunodeficiency virus type 1 and other enveloped viruses

We have examined a novel betain-type fluoroalkylated oligomer, RD6-2198, for its inhibitory effects on the replication of human immunodeficiency virus type 1 (HIV-1) and other enveloped viruses, including herpes simplex virus types 1 and 2 (HSV-1 and HSV-2, respectively) and respiratory syncytial virus (RSV) in cell cultures. We have found that the compound is a potent and selective inhibitor of these viruses. RD6-2198 inhibited the replication of HIV-1IIIB at a concentration of 0.85 microg/ml with a selectivity index greater than 59 in MT-4 cells. Furthermore, its 50% effective concentration (EC50) values for HSV-1, HSV-2 and RSV, were 0.51, 0.94 and 3.0 microg/ml, respectively. We found that the RD6-2198 suppressed the gp120-CD4 interaction (as monitored by an enzyme-linked immunosorbent assay (ELISA) method). RD6-2198 also inhibited the binding of anti-gp120 monoclonal antibody to gp120 expressed on MOLT-4/IIIB cells (MOLT-4 cells chronically infected with HIV-1IIIB). However, the compound did not inhibit the interaction of anti-CD4 antibody with CD4. These results suggest that RD6-2198 interacts with the viral envelope glycoprotein and thereby inhibits the viral adsorption process. In addition, RD6-2198 was also found to suppress the proliferation of MOLT-4/IIIB cells. When applied topically, RD6-2198 at a concentration of 10 mg/ml completely protected mice from an intravaginal HSV-2 infection.

[Telomerase: a new marker for cancer diagnosis]

Telomerase, a ribonucleoprotein reverse transcriptase, is expected to be a new marker for cancer diagnosis since it has been reported that high expression of telomerase activity was detected exclusively in germinal tissues and tumor tissues in human body, which is further evaluated by improvement of quantitative assay procedure for telomerase activity in tissue extract and by development of in situ detection method of telomerase protein component in tissue sections.

Propentofylline potentiates induced ischemic tolerance in gerbil hippocampal neurons via adenosine receptor

The effect of propentofylline, an adenosine uptake inhibitor, on ischemic tolerance was investigated in the gerbil global ischemia model. Propentofylline was administered 24 hours after short preconditioning ischemia, and animals were subjected to 5-minute ischemia 24 hours thereafter. Propentofylline at a dose of 20 mg/kg intraperitoneally, but not at a dose of 10 mg/kg, significantly potentiated the protective effect of preconditioning ischemia in the CA1 hippocampal neurons. This effect was completely abolished by simultaneous administration of theophylline (20 mg/kg), an adenosine receptor blocker. This finding suggests the involvement of adenosine receptor for the development of ischemic tolerance.

Hypercapnia enhances the development of coughing during continuous infusion of water into the pharynx

We investigated the effects of increasing CO2 ventilatory drive on the coordination of respiration and reflex swallowing elicited by continuous infusion of distilled water into the pharynx (2.5 ml/min) in 11 normal subjects. Ventilation was monitored using a pneumotachograph and swallowing was recorded by submental electromyogram. The CO2 ventilatory drive was increased by addition of external dead space, while ventilation, the frequency of swallows, and the timing of swallows in relation to the phases of the respiratory cycle were measured at steady-state conditions. We found that the CO2 ventilatory response is not influenced by continuous reflex swallowing but that hypercapnia influences the timing and frequency of these swallows. Signs of aspiration were never observed during continuous infusion of water at eucapnia, but seven of 11 subjects showed laryngeal irritation and/or pending aspiration during hypercapnia, and the incidence of laryngeal irritation was higher the greater the PCO2. Detailed analysis of laryngeal irritations consisting of single coughs in seven subjects revealed that the majority of laryngeal irritations occurred when swallows coincided with expiratory-inspiratory transition or when swallows coincided with inspiration, whereas laryngeal irritation after an expiratory swallow was never observed. These results suggest that the automatic respiratory control system is not influenced by continuous swallowing but that the coordination of swallowing and respiration may be compromised during hypercapnia.

The inhibitory influence of pulmonary vagal afferents on respiratory distress induced by airway occlusion in halothane-anesthetized cats

Although the sensation of dyspnea is common, the mechanisms underlying the sensation have not been fully elucidated. Dyspnea, which is a subjective sensation induced by various respiratory and nonrespiratory stimuli, ranges in intensity from an awareness of difficulty in breathing to an incapacitating state of respiratory distress. It need not be an all or none concept when tolerable; however, intolerable dyspnea is often accompanied by some kind of escape response. In a previous study, we developed a new concept of minimum alveolar anesthetic concentration for airway occlusion (MAC-AOR). Using this model, we assessed the influence of pulmonary vagal afferents on respiratory distress induced by airway occlusion. Adult cats (n = 13) of both sexes weighing 2.7-5.6 kg (3.9 +/- 0.3 kg, mean +/- SE) were anesthetized with halothane and tracheally intubated. After determination of MAC-AOR, anesthesia was maintained with the highest concentration of halothane permitting the positive motor response identified by visual inspection or electromyogram (EMG) of the forearm, usually of the head or extremities. Twisting or jerking of the head was considered a positive response, but twitching or grimacing was not. A slight movement of the shoulder and/or the extremities was not considered positive, nor were coughing, swallowing and chewing, or rigidity recognized as the increase of tonic activity on the forearm EMG. The duration from the start of airway occlusion to the onset of the positive response (DOCCL) was considered as behavioral measures of the tolerable limit of respiratory distress. DOCCL was measured before (Control 1), during, and after (Control 2) lung expansion induced by the injection of the inhaled gas of 5 mL/kg or 10 mL/kg (LE5 or LE10) at functional residual capacity level. Subsequently, 6 of 13 cats received bilateral vagotomies, and the same procedure was repeated at the same concentration as stated above. Then, MAC-AOR after vagotomy was determined again. Before vagotomy, the values of DOCCL during lung expansion (238 +/- 30 s during LE5 and 288 +/- 24 s during LE10) were significantly longer than Control 1 (169 +/- 29 s) and Control 2 (154 +/- 29 s) values (P < 0.01). After vagotomy, the effect of lung expansion on DOCCL was totally abolished. MAC-AOR after vagotomy (1.4% +/- 0.1%) was significantly higher than that before vagotomy (1.1% +/- 0.1%) (P < 0.01). We have demonstrated that vagotomy abolishes the prolongation effect of the lung expansion on DOCCL and increases the value of MAC-AOR in this animal model. These results suggest that pulmonary vagal afferents play an important role in relief of respiratory distress developed during airway occlusion.

IMPLICATIONS

In anesthetized cats, we found that lung expansion reduces the tolerable limit to airway occlusion and vagotomy decreased minimum alveolar anesthetic concentration for airway occlusion, which suggests that pulmonary vagal afferents play an important role in relief of respiratory distress.