[Progress of researches on infection with two species of Echinococcus causing human diseases in animal hosts and influencing factors]

Echinococcosis is a serious zoonotic parasitic disease caused by infections with larval Echinococcus. The life cycle of Echinococcus involves a variety of animal hosts, including hoofed animals and rodents as intermediate hosts and carnivores as definitive hosts. The transmission of human echinococcosis is closely associated with the life cycle of E. granulosus and E. multilocularis among animal hosts in nature. This review summarizes the recent advances in the prevalence and influencing factors of E. granulosus and E. multilocularis infections in animal hosts, so as to provide insights into precision control of echinococcosis.

Advances in research on echinococcoses epidemiology in China

Echinococcoses are serious zoonotic diseases in China's vast, western and north-western pastoral areas that has one of the highest prevalence in the world. The two most common forms, cystic echinococcosis (CE) and alveolar echinococcosis (AE), are co-epidemic in some areas causing a grave threat to people's health and economic development. Echinococcus spp. are transmitted through domestic, sylvatic and mixed cycles involving many kinds of host. Successful transmission requires a favourable environment for the growth of the parasites and survival of their eggs, while the unique customs and religious beliefs in the endemic areas pose a challenge to the prevention and control of these parasites. Based on previous epidemiological studies, this paper reviews the particular factors affecting the transmission of Echinococcus parasites in China, with a focus on biological (parasite genotype and the species, age, sex and density of hosts), environmental (landscape and climate) and social (age, gender, ethnicity, education, occupation, life style, cultural customs, living conditions and hygiene practices of humans in the endemic areas). These three factors interact with each other and jointly determine the parasites' transmission intensity, the study of which supports the formulation of the strategies and measures that are significant for control of these infections.

Assessment of China's contributions to the Regional Network for Asian Schistosomiasis and Other Helminth Zoonoses: a questionnaire survey

Background

The Regional Network for Asian Schistosomiasis and Other Helminth Zoonoses (RNAS⁺) was established in 1998, which has developed close partnerships with Asian countries endemic for schistosomiasis and other helminthiasis in Asia. RNAS⁺ has provided an ideal regional platform for policy-makers, practitioners and researchers on the prevention, control and research of parasitic diseases in Asian countries. China, one of the initiating countries, has provided significant technical and financial support to the regional network. However, its roles and contributions have not been explored so far. The purpose of this study was to assess China's contributions on the supporting of RNAS⁺ development.

Methods

An assessment research framework was developed to evaluate China’s contributions to RNAS⁺ in four aspects, including capacity building, funding support, coordination, and cooperation. An anonymous web-based questionnaire was designed to acquire respondents’ basic information, and information on China’s contributions, challenges and recommendations for RNAS⁺development. Each participant scored from 0 to 10 to assess China’s contribution: “0” represents no contribution, and “10” represents 100% contribution. Participants who included their e-mail address in the 2017–2019 RNAS⁺ annual workshops were invited to participate in the assessment.

Results

Of 71 participants enrolled, 41 responded to the survey. 37 (37/41, 90.24%) of them were from RNAS⁺ member countries, while the other 4 (4/41, 9.76%) were international observers. Most of the respondents (38/41, 92.68%) were familiar with RNAS⁺. Respondents reported that China’s contributions mainly focused on improving capacity building, providing funding support, coordination responsibility, and joint application of cooperation programs on RNAS⁺ development. The average scores of China’s contributions in the above four fields were 8.92, 8.64, 8.75, and 8.67, respectively, with an overall assessment score of 8.81 (10 for a maximum score). The challenge of RNAS⁺ included the lack of sustainable funding, skills, etc. and most participants expressed their continual need of China’s support.

Conclusions

This survey showed that China has played an important role in the development of RNAS⁺ since its establishment. This network-type organization for disease control and research can yet be regarded as a great potential pattern for China to enhance regional cooperation. These findings can be used to promote future cooperation between China and other RNAS⁺ member countries.

Biological Characteristics and Molecular Mechanisms of Fludioxonil Resistance in Fusarium graminearum in China

Fusarium graminearum is the primary causal agent of Fusarium head blight (FHB) of wheat. The phenylpyrrole fungicide fludioxonil is not currently registered for the management of FHB in China. The current study assessed the fludioxonil sensitivity of a total of 53 F. graminearum isolates collected from the six most important wheat-growing provinces of China during 2018 and 2019. The baseline fludioxonil sensitivity distribution indicated that all of the isolates were sensitive, exhibiting a unimodal cure with a mean effective concentration for 50% inhibition value of 0.13 ± 0.12 μg/ml (standard deviation). Five fludioxonil-resistant mutants were subsequently induced by exposure to fludioxonil under laboratory conditions. Ten successive rounds of subculture in the absence of the selection pressure indicated that the mutation was stably inherited. However, the fludioxonil-resistant mutants were found to have reduced pathogenicity, higher glycerol accumulation, and higher osmotic sensitivity than the parental wild-type isolates, indicating that there was a fitness cost associated with fludioxonil resistance. In addition, the study also found a positive cross resistance between fludioxonil, procymidone, and iprodione, but not with other fungicides such as boscalid, carbendazim, tebuconazole, and fluazinam. Sequence analysis of four candidate target genes (FgOs1, FgOs2, FgOs4, and FgOs5) revealed that the HBXT2R mutant contained two point mutations that resulted in amino acid changes at K223T and K415R in its FgOs1 protein, and one point mutation at residue 520 of its FgOs5 protein that resulted in a premature stop codon. Similarly, the three other mutants contained point mutations that resulted in changes at the K192R, K293R, and K411R residues of the FgOs5 protein but none in the FgOs2 and FgOs4 genes. However, it is important to point out that the FgOs2 and FgOs4 expression of all the fludioxonil-resistant mutants was significantly (P < 0.05) downregulated compared with the sensitive isolates (except for the SQ1-2 isolate). It was also found that one of the resistant mutants did not have changes in any of the sequenced target genes, indicating that an alternative mechanism could also lead to fludioxonil resistance.

[SWOT analysis of schistosomiasis elimination in Laos]

OBJECTIVE

To analyze the advantages, disadvantages, opportunities and challenges for schistosomiasis elimination in Laos, so as to propose the corresponding healthy policies and suggestions.

METHODS

A SWOT analysis was performed to analyze the strength, weakness, opportunity and threat for the schistosomiasis elimination program in Laos, and the corresponding policy suggestions were proposed.

RESULTS

The national schistosomiasis elimination program of Laos receives governmental emphases and great supports. A strategy based on mass drug administration was proposed and a sentinel site-bases surveillance system has been built for schistosomiasis elimination in Laos; however, there are several challenges for the national schistosomiasis elimination program in Laos, including insufficient financial supports, inadequate professional capability, weak schistosomiasis control awareness in community populations and difficulty in vector control.

CONCLUSIONS

Persistent governmental leadership, increasing financial supports, strengthening professional team building and improving schistosomiasis control awareness in community populations are required to facilitate the progress towards schistosomiasis elimination in Laos.

From parasitic disease control to global health: New orientation of the National Institute of Parasitic Diseases, China CDC

As the only specialized institution for research and control of parasitic diseases at the national level in China for almost 70 years, the National Institute of Parasitic Diseases (NIPD) at the Chinese Center for Disease Control and Prevention (China CDC) has been instrumental in supporting the remarkable progress from high prevalence to transmission interruption or low endemicity of several diseases, lymphatic filariasis, malaria and schistosomiasis in particular. This has taken place through technical guidance, emergency response and scientific research as well as providing technical service, education, training, health promotion and international cooperation. With China's increasing involvement in international cooperation and the increased risk for (re)emerging tropical diseases in mind, the Chinese Government designated in 2017 a new Chinese Center for Tropical Disease Research to NIPD. Responding to the expanded responsibilities, the institute is scaling up its activities in several ways: from parasitic diseases to the wider area of tropical diseases; from disease control to disease elimination; from biological research to policy evidences accumulation; and from public health to global health. Based on this new vision and China's previous accomplishments in the areas mentioned, the institute is in a position to move forward with respect to global health and equitable development according to the central principles of the United Nations' Sustainable Development Goals.

A path to cooperation between China and Mongolia towards the control of echinococcosis under the Belt and Road Initiative

Health is the core of development. Health cooperation between countries plays a pivotal role under the Belt and Road Initiative (B&R). In 2013, China launched its B&R to improve the international cooperation of which health was an important component. As one of the neglected zoonotic diseases, echinococcosis has become a public health concern and is on top of the government agenda among neglected zoonosis in Mongolia. The transmission of the disease involves animal husbandry, and its characteristics determine the prevention and control of such diseases which requires cross-sector collaboration and comprehensive prevention and control strategies. Taking echinococcosis as an entry point and adopting a 'Mongolia-led, China-supported, and results-sharing' approach to public health cooperation will not only contribute to the advancement of Mongolia's national health coverage, but also promoting China's capacity to engage in global health. In this way, it contributes to meeting the sustainable development goals, especially goal 3, target 3.3: by 2030, end the epidemics of AIDS, tuberculosis, malaria and neglected tropical diseases and combat hepatitis, water-borne diseases and other communicable diseases. This paper provides an overview on how the cooperation between China and Mongolia under the context of B&R was initiated, planned and moved forward to implementation. The experience may provide a good model and inform policy and practice for other bilateral cooperations.

[Effect of aerobic exercise and resistance exercise in improving non-alcoholic fatty liver disease: a randomized controlled trial]

Objective: To investigate the effect of dietary control combined with different exercise modes on plasma vaspin, irisin, and metabolic parameters in patients with non-alcoholic fatty liver disease (NAFLD) through a randomized open parallel-controlled study. Methods: The patients aged 30-65 years who visited Tianjin Third Central Hospital from January 2013 to December 2014 and were diagnosed with NAFLD by liver ultrasound and fat content determination were screening, and 474 patients were enrolled in this randomized controlled trial and divided into aerobic exercise group, resistance exercise group, and control group. All patients received dietary intervention. The three groups were compared in terms of biochemical parameters, fat content, NFS score, energy metabolic parameters, body composition index, and levels of vaspin and irisin at baseline and after 6 months of intervention. SPSS 19.0 was used for statistical analysis. The t-test, the Mann-Whitney U test, the chi-square test, and an analysis of variance were used for comparison between groups. The multiple imputation method was used for missing data, and the results were included in the intention-to-treat analysis. Results: There were no significant differences in age, sex, anthropometrical parameters, and biochemical parameters between the three groups at baseline. Compared with dietary control alone, aerobic exercise and resistance exercise helped to achieve significant reductions in waist circumference, diastolic pressure, percentage of body fat, volatile fatty acid, fasting blood glucose, homeostasis model assessment of insulin resistance, triglyceride, low-density lipoprotein cholesterol, free fatty acid, uric acid, alanine aminotransferase, and liver fat content after 6 months of intervention (P < 0.05). The aerobic exercise group had a significant increase in non-protein respiratory quotient and significant reductions in body mass index and aspartate aminotransferase after intervention, as well as a significant increase in resting energy expenditure and significant reductions in abdominal fat ratio and total cholesterol after 6 months of resistance exercise (P < 0.05). The aerobic exercise group and the resistance exercise group had a significant reduction in vaspin and a significant increase in irisin after intervention (P < 0.05), and the resistance exercise group had significantly greater changes in these two adipokines than the aerobic exercise group (P < 0.05). Conclusion: Exercise therapy is an effective method for the treatment of metabolism-associated diseases, and a combination of resistance and aerobic exercises is more reasonable and effective in clinical practice. As a relatively safe exercise mode, resistance exercise can also effectively improve the metabolic state of NAFLD patients.

New insights on serodiagnosis of trichinellosis during window period: early diagnostic antigens from Trichinella spiralis intestinal worms

The clinical diagnosis of trichinellosis is difficult because its clinical manifestations are nonspecific. Detection of anti-Trichinella IgG by ELISA using T. spiralis muscle larval excretory-secretory (ES) antigens is the most commonly used serological method for diagnosis of trichinellosis, but the main disadvantage is false negativity during the early stage of infection. There is an obvious window period between Trichinella infection and antibody positivity.

During the intestinal stage of Trichinella infection, the ES antigens of intestinal worms (intestinal infective larvae and adults) are exposed to host’s immune system at the earliest time and elicit the production of specific anti-Trichinella antibodies. Anti-Trichinella IgG antibodies in infected mice were detectable by ELISA with ES antigens of intestinal worms as soon as 8–10 days post infection (dpi), but ELISA with muscle larval ES antigens did not permit detection of infected mice before 12 dpi. Therefore, the new early antigens from T. spiralis intestinal worms should be screened, identified and characterized for early serodiagnosis of trichinellosis.

China-Africa cooperation initiatives in malaria control and elimination

Malaria has affected human health globally with a significant burden of disease, and also has impeded social and economic development in the areas where it is present. In Africa, many countries have faced serious challenges in controlling malaria, in part due to major limitations in public health systems and primary health care infrastructure. Although China is a developing country, a set of control strategies and measures in different local settings have been implemented successfully by the National Malaria Control Programme over the last 60 years, with a low cost of investment. It is expected that Chinese experience may benefit malaria control in Africa. This review will address the importance and possibility of China–Africa collaboration in control of malaria in targeted African countries, as well as how to proceed toward the goal of elimination where this is technically feasible.

[Retrospective analysis of granted projects of the National Institute of Parasitic Disease, China CDC during 2002-2012]

In this paper, the granted projects of the National Institute of Parasitic Diseases (NIPD), China CDC, was analyzed. The results showed that from 2002 to 2012, 126 projects were granted to NIPD. 28.6% (36/126) of the projects were at the national level; 27% (34/126) were at provincial and ministrerial level. International cooperation projects and those supported by state key laboratory and enterprises accounted for 28.6% (36/126) and 15.8% (20/126), respectively. 94 projects belonged to applied researches and 32 belonged to basic researches. Most project leaders were young and middle-aged researchers with senior professional titles.

[Brief discussion on experiences from laboratory certification and accreditation on detection of parasitic diseases]

The laboratory certification and accreditation is the development trend of domestic and international laboratories. The National Institute for Parasitic Diseases, Chinese Center for Disease Control and Prevention passed through the site assessment in September 2012 successfully, 26 items in 8 fields declared were all adopted. This article summarizes some work experiences during carrying out the laboratory certification and accreditation.

[Risk assessment on laboratory biosafety of Leishmania]

OBJECTIVE

To provide the evidence for improving the risk assessment and personal protective equipment and techniques to laboratory staff related to Leishmania.

METHODS

The laboratory biosafety of Leishmania was preliminarily assessed based on the biological background information, potential hazards in experimental activities, the risk analyses of laboratory personnel and other relevant factors.

RESULTS

The risk assessment on laboratory biosafety of Leishmania was helpful for the establishment of the laboratory standard operating procedure, and was helpful for protecting the staff from infection of Leishmania.

CONCLUSION

The risk assessment on laboratory biosafety is important to the safety of laboratory activity related to Leishmania, and is of a great significance to protect the laboratory staff.

[Geographical distribution of echinococcosis among children in Qinghai Province]

OBJECTIVE

To analyze the epidemiological status of echinococcosis among children in three different zones of Qinghai Province.

METHODS

B-ultrasound and ELISA were used in the survey to evaluate echinococcus infection among 6 to 15 year old children in the three zones, namely, Qinghai southern plateau, Qilian mountain-Hehuang valley and Chaidamu basin.

RESULTS

The prevalence of echinococcus infection scanned by B-ultrasound and sera positive rate detected by ELISA in children were 1.5% (320/20 730) and 6.5% (1024/15 762) respectively, and the prevalence of cystic echinococcosis and alveolar echinococcosis by ultrasound were 1.0% (206/20730) and 0.6% (114/20730), respectively. The prevalence and sera positive rate were 9.5% (707/7 453) and 2.3% (269/11 618) in Qinghai southern plateau, 3.8%(289/7 544) and 0.6% (50/8 275) in Qilian mountain-Hehuang valley, and 3.7% (28/765) and 0.1% (1/837) in Chaidamu basin, respectively. The southern plateau showed the highest prevalence, with a significant statistical difference among the three areas (P < 0.01). The prevalence of alveolar echinococcosis was 1.0% (114/11 618) in the southern plateau, but no alveolar echinococcosis patients were found in other two areas. Correlation analysis showed that the prevalence increased with the altitude (r(s-e) = 0.96, P < 0.05, R2 = 0.93; r(p-e) = 0.82, P < 0.05, R2 = 0.67).

CONCLUSION

The prevalence of echinococcosis among children shows an apparent geographical difference in Qinghai Province.

Distribution of the intermediate hosts of Echinococcus multilocularis in Shiqu County, Sichuan, China

BACKGROUND

The rodentia and lagomorpha animals are the intermediate hosts of Echinococcus multilocularis, their distribution and infection of this parasite may facilitate the infection of definitive hosts such as dogs. The aim of this study was to determine the distribution of the intermediate hosts of Echinococcus multilocularis in Shiqu County, Sichuan, China.

METHODS

A systematic sampling method was used to investigate the density of burrows of rodents and lagomorphs at 97 pasture sites in winter and summer pastureland and remote sensing (RS) technology was used to correlate their densities to the distribution of these animals in different landscape types.

RESULTS

Based on the densities of Ochotona curzoniae, Microtus fuscus (dependent variable) and their burrow densities (independent variable) in survey points, regression equations were fitted respectively (Ochotona curzoniae, P < 0.0001, R(2) = 0.8705; Microtus fuscus, P < 0.0001, R(2) = 0.9736). Their burrow density in summer pastureland was higher than in winter pastureland (F = 36.65, P < 0.0001). The burrow densities of Ochotona curzoniae and Microtus fuscus in bareland and half-bareland are higher than in grassland (F = 7.73, P < 0.001).

CONCLUSIONS

The regression relationship between the densities of Ochotona curzoniae and Microtus fuscus and their burrow densities indicate that the burrow densities could reflect the animal densities and that the burrow density was greater in summer pastureland than in winter pastureland. The main distribution areas of the intermediate hosts were in bareland and half-bareland.

[Cloning, expression and immunodiagnostic evaluation of antigen EPC1 from Echinococcus granulosus]

OBJECTIVE

To clone and express EPCl gene of Echinococcus granulosus, and investigate its immunogenicity and diagnostic value.

METHODS

Total RNA was extracted from hydatid cyst protoscoleces and EPC1 gene of Echinococcus granulosus was amplified by RT-PCR. The PCR product was cloned into pGEM-T vector, and then subcloned into the prokaryotic expression vector PET28a(+). The positive recombinants were transformed into Escherichia coli BL21 (DE3), and followed by expression of the protein induced by IPTG. The recombinant protein was identified by SDS-PAGE and Western blotting, and used to establish ELISA. Serum samples from patients with cystic echinococcosis (60 cases), alve-olar echinococcosis (37 cases), cysticercosis (16 cases), clonorchiasis sinensis (7 cases), schistosomiasis japonica (4 cases) and healthy persons (33 cases) were examined.

RESULTS

The recombinant plasmid PET28a-EgEPC1 was identified by restriction enzyme digestion and sequencing. SDS-PAGE result showed that the recombinant containing recombinant plasmid PET28a-EgEPC1 expressed a soluble fission protein of EgEPC1 (about M, 11 000). The protein was recognized by pool sera of cystic echinococcosis patients. The overall sensitivity and specificity of diagnosis by ELISA for cystic echinococcosis were 78.3% (47/60), and 98.3% (59/60), respectively. The cross reaction with sera of alveolar echinococcosis was 40.5% (15/37).

CONCLUSION

The recombinant EgEPC1 antigen has diagnostic value in cystic echinococcosis.

[Multiplex PCR for analysis of the Plasmodium falciparum drug resistance molecular markers]

OBJECTIVE

To develop a multiplex PCR protocol for amplification of five Plasmodium falciparum drug resistance related genes, thereby facilitate the rapid and high throughput analysis of the drug resistance molecular markers.

METHODS

Five pairs of primers were designed according to the reference sequences by using Primer Premier 5.0 and Oligo 6.0 software. Drug resistance related genes, including P. falciparum chloroquine resistance transporter (Pfcrt), multi-drug resistance 1 (Pfmdr1), dihydropteroate synthetase (Pfdhps), dihydrofolate reductase (Pfdhfr) and sarco/endoplasmic reticulum Ca2+-ATPase (PfATPase6), were amplified by single-tube multiplex PCR using Hot Start Taq DNA Polymerase among negative controls (P. vivax, P. berghei, P. cynomolgi, Leishmania donovani, Cryptosporidium andersoni), blank control (using H2O as template), as well as P. falciparum laboratory isolates (3D7, Dd2, HB3, FCC1/HN and CMH/YN) and field samples (collected from Yunnan, Hainan of China and Myanmar). After amplification, the PCR products were analyzed by agarose gel electrophoresis. The sequencing results were aligned to the reference sequence using BLAST.

RESULTS

Five expected bands at 315, 437, 514, 594 and 770 bp were obtained with no additional or nonspecific products in P. falciparum laboratory isolates and field samples. The sequencing results were identical with the reference sequence except the polymorphism sites, and exhibited more than 98.5% homology. The multiplex amplification was performed successfully starting from 0.1 ng of DNA template. No band was observed in negative controls and blank control.

CONCLUSION

The present study establishes a method to amplify five Plasmodium falciparum drug resistance related genes harboring 21 SNPs by one-tube reaction. The multiplex PCR protocol showing high specificity and sensitivity is more convenient and efficient in analyzing the P. falciparum drug resistance molecular markers as compared with traditional nested PCR.

[The point mutations in Pfcrt and Pfmdr1 genes in Plasmodium falciparum isolated from Hainan Province]

OBJECTIVE

To evaluate the point mutations in Pfcrt and Pfmdr1 genes in Plasmodium falciparum isolated from Hainan Province.

METHODS

Nested polymerase chain reaction and restriction fragment length polymorphism were used to detect the point mutations at codon 76 of Pfcrt and at codon 86, 1246 of Pfmdr1 in P. falciparum isolates. Chloroquine resistance was measured by the in vitro microtest recommended by WHO.

RESULTS

In 36 samples tested, 28 were successfully amplified for Pfcrt, 64.3% of them carried mutant allele at codon 76, 21.4% with wild allele K76 and 14.3% with mixed allele mutation. While for Pfmdr1, 3.4% isolates displayed the 86Y mutation, 89.7% with wild allele N86 and 6.9% with the mixed alleles in 29 isolates which were amplified successfully for N86Y. No point mutation in Pfmdr1 at codon 1246 was found in 13 isolates from the total 36 samples. By the in vitro test, 72.2% (26/36) showed resistance to chloroquine. The 76T and 86Y mutant alleles were present in both in vitro susceptible and resistant isolates. There was a significant difference between susceptible and resistant isolates carrying 76T mutant codon (P < 0.05), but no significant difference was found in Pfmdr1 (P < 0.05).

CONCLUSION

There is a significant difference of the 76T prevalence in Pfcrt gene between the susceptible isolate and resistant one of P. falciparum to chloroquine in vitro. The Pfcrt 76T may be used as a predictive marker for chloroquine resistance surveillance.

Contractile responses of diabetic rat aorta to phenylephrine at different stages of diabetic duration

AIM

To investigate the time-dependent changes in contractile responses of aorta to phenylephrine (Phe) in diabetic rats and age-matched control, and its possible mechanism.

METHODS

At stages of 2-, 6-, and 12-week diabetic duration, aortic rings were studied for contractile responses to agonists in vitro.

RESULTS

At the stage of 2-week diabetic duration, contractile responses to lower concentrations of phenylephrine were increased (P < 0.05), but the maximal contraction of phenylephrine did not change. At the stage of 6-week diabetic duration, contractile responses to phenylephrine were increased (P < 0.01) at each concentration, and the maximal contraction was increased by approximately 40 %. However, at the stage of 12-week diabetic duration: 1) the maximal contractile response to Phe 10 micromol . L-1 was decreased (P < 0.05), 2) in Ca2+ free edetic acid medium, Phe 10 micromol . L-1-induced transient contraction was also decreased (P < 0.05), 3) in Ca2+ free edetic acid medium, in the presence of nifedipine 10 micromol . L-1 and Phe 10 micromol . L-1, the Ca2+ repletion-caused contraction was not different from control, 4) in normal medium, cyclopiazonic acid (CPA) 10 micromol . L-1-induced contraction was decreased (P < 0.01).

CONCLUSION

The results suggested that contractile responses to phenylephrine in diabetic rat aorta changed with the development of diabetes, and the changes of functional Ca2+ store sizes and Ca2+ entry mainly through voltage-dependent Ca2+ channels were responsible for the alterations of contractile responses to phenylephrine in diabetes.

Effects of Scutellarein on diabetic rat aorta

AIM

To study the effect of Scutellarein (Scu) on the diabetic rat aorta.

METHODS

Contractile responses to phenylepherine and endothelium-dependent relaxation responses to acetylcholine (ACh) in rat aorta were investigated after streptozocin-induced 6-wk diabetes, Scu-treated streptozocin-induced diabetes, and in age-matched control in vitro.

RESULTS

1) Endothelium-dependent relaxation to ACh in diabetic rats was decreased (P < 0.01) compared with age-matched control. 2) Contractile responses to phenylepherine were increased (P < 0.01) in diabetic rats. 3) The dietary supplement of 0.5% Scu starting from 1-wk diabetes induction prevented endothelial dysfunction (P < 0.01), but the contractile responses to phenylepherine were further increased.

CONCLUSION

Scu prevented vascular endothelial dysfunction in diabetic rats, and also potentiated the contraction induced by phenylepherine.

Erigeron breviscapus prevents defective endothelium-dependent relaxation in diabetic rat aorta

We examined the endothelium-dependent relaxation response to acetylcholine (Ach) in streptozotocin-induced diabetic rat aorta at the stages of 2- and 6-wks' duration in vitro, and compared with another two groups which were treated with dietary supplement of 0.1% Aminoquanidine (AG) and 0.5% Erigeron breviscapus (EB) from 1-week of diabetes induction. At the stage of 2-wks' duration of diabetes, relaxation responses to lower concentrations of Ach in 0.3 uM phenylepherine-precontracted aortas were diminished significantly (P<0.05) compared with age-matched control, but the maximal relaxation of Ach remained unchanged. At the stage of 6-wks' duration, diabetes caused an approximately 60% (P<0.001) deficit in maximum relaxation, and this was significantly (P<0.001) prevented in AG and EB treated groups. There was an approximately 40% enhancement in the maximum contractile response to phenylepherine with diabetes (P<0.05), which was unaffected significantly by AG and EB treatments. The data suggest that the defective endothelium-dependent relaxation in diabetic rat aorta occurred as early as 2-wks' duration of diabetes, and the treatments of AG and EB could protect vascular endothelium although the deficits in vascular smooth muscle contractile responses were not protected.

Effects of erythrocyte lysate of different incubation times on intracellular free calcium in rat basilar artery smooth-muscle cells

OBJECT

The purpose of this study was to characterize substance(s) in the erythrocytes that increase intracellular free Ca++ concentration ([Ca++]i) in smooth-muscle cells and that therefore may be involved in the pathogenesis of vasospasm.

METHODS

Because vasospasm occurs days after subarachnoid hemorrhage (SAH), the authors studied the effects of aged human erythrocyte hemolysate and its low-molecular-weight (LMW) and high-molecular-weight (HMW) fractions on [Ca++]i in freshly isolated rat basilar artery smooth-muscle cells. Fresh hemolysate (Day 0) produced a biphasic response consisting of a transient peak and a sustained plateau increase in [Ca++]i, whereas hemolysate prepared from cells incubated for 3, 7, or 14 days induced only a transient response without a sustained phase. The effect of hemolysate declined with increasing incubation time. The HMW fraction and purified human oxyhemoglobin (OxyHb) did not evoke a response. The LMW fraction from Days 3, 7, or 14 produced no response at low concentrations (< 10%) and a transient response at high concentrations (> 20%), and the effect diminished with increasing incubation time. Unfractionated hemolysate or the LMW fraction of hemolysate incubated for 21 days produced no response. The combination of the 10% LMW fraction from Day 3 plus the 10% HMW fraction (Days 3. 7, 14, or 21) transiently increased [Ca++]i,. However, [Ca++]i was not changed by the 10% LMW fraction from Day 14 plus the 10% HMW fraction from Day 3 or 14. In the presence of OxyHb, [Ca++]i was increased by the 10% LMW fraction on Days 3 and 7, but not by the LMW fraction from Days 14 or 21.

CONCLUSIONS

The decline over time in the effect of hemolysate on [Ca++]i indicates either that the time that substances are released from erythrocytes is important in the generation of vasospasm or that this experimental system as used is not representative of conditions present after SAH. The data indicate that the ability to elevate [Ca++]i in smooth-muscle cells with hemolysate is provided by multiple substances, including OxyHb. These substances may interact during specific times after incubation of erythrocytes in vitro.

Comparison of the Ca2+ movement by activation of alpha1-adrenoceptor subtypes in HEK-293 cells

We studied the Ca2+ movement induced by activation of alpha1A-, alpha1B- and alpha1D-adrenoceptor subtypes in transfected HEK-293 cells with the fura-2 probe. All these alpha1-AR subtypes induced both Ca2+ release and Ca2+ entry. The effect on Ca2+ release in alpha1b transfected HEK-293 cells was bigger than that in alpha1a and alpha1d transfected HEK-293 cells, and the effects on Ca2+ entry were the same in alpha1a, alpha1b and alpha1d transfected HEK-293 cells. The Ca2+ entry was inhibited by 1 mM NiSO4, but not by nifedipine. Cyclopiazonic acid (CPA) produced a biphasic Ca2+ signal response in Ca2+ medium, and only induced a transient response in Ca2+-free medium. After depletion of CPA-sensitive Ca2+ pool by 10 microM CPA in Ca2+-free medium, 10 microM adrenaline (Adr) still transiently increased [Ca2+]i in three different alpha1-adrenoceptor subtype transfected HEK-293 cells. However, after depletion of adrenaline-sensitive Ca2+ pool by 10 microM Adr, CPA transiently elevated [Ca2+]i only in alpha1a and alpha1d transfected HEK-293 cells, not in alpha1b transfected HEK-293 cells. U73122, a phospholipase C (PLC) inhibitor, inhibited both Ca2+ release and Ca2+ entry induced by activation of alpha1A alpha1B and alpha1D subtypes in transfected HEK-293 cells. These results suggest that HEK-293 cell line contains two functionally separate intracellular Ca2+ pools, CPA-sensitive and Adr-sensitive pools. Activation of alpha1B-AR stimulates Ca2+ release from both CPA-sensitive and Adr-sensitive Ca2+ pools. Alpha1A and alpha1D subtypes induce Ca2+ release only from Adr-sensitive Ca2+ pool.

In vitro inhibitory effects of chebulinic acid on the contractile responses of cardiovascular muscles

1. The effects of chebulinic acid, which has been shown to elicit blood pressure lowering effect in rats, on aortic vascular contraction as well as cardiac contraction were studied in rats. 2. Chebulinic acid had no effect on KCl-induced aortic contraction, but irreversibly inhibited the contractile responses to phenylephrine in an apparently non-competitive manner. Chebulinic acid also inhibited contractile responses of rat aorta to 5-hydroxytryptamine and angiotensin II. 3. Chebulinic acid inhibited the binding of [3H]-prazosin to dog aortic microsomal membranes in a concentration-dependent manner with an IC50 value of 0.34 mmol/L. Results of saturation binding experiments suggest a mixed mode of inhibition by chebulinic acid (i.e. a decrease in both the maximal number of binding sites and the affinity for prazosin). 4. Chebulinic acid concentration-dependently and reversibly inhibited the maximal left ventricular pressure of rat heart in a Langendorff preparation with 50% inhibition occurring at a concentration of 0.3 nmol/L. 5. We conclude that chebulinic acid exerts non-specific inhibitory actions in vascular preparations. Its inhibitory effect on cardiac contraction was reversible and three orders of magnitude more potent than that on vascular contraction. We suggest that the hypotensive effect of chebulinic acid is probably mediated via the decrease in cardiac output resulting from reduced left ventricular contraction.

Two-state stochastic models for memory in ion channels

AIM

To study quantitatively the memory existing in ion channels.

METHODS

Stochastic processes were used to model 2 categories of memory (short-term and long-term) by persisting in the standpoint of two-state, instead of multiple states, but with different transition mechanism.

RESULTS

A two-state Markov process with constant transition intensities well fitted the short-term memory and a two-state Markov process within a kind of random environment well fitted the long-term memory. Statistical procedures for parameter estimation were proposed and demonstrated with 2 real examples on the channels of PC12 cells.

CONCLUSION

The memory in ion channels can be quantitatively modelled as stochastic process with 2 states.

Existence of memory in ion channels

AIM

To explore the existence of memory in Ca(2+)-dependent K+ channels of cultured aortic smooth muscle cells (ASMC) and voltage-dependent K+ channels of clonal pheochromocytoma (PC12) cells.

METHODS

Calculating the sample auto-correlation functions based on the digitized signals or the 0-1 series corresponding to closing and opening of the channels after routine evaluation, rather than the sequence of sojourn times.

RESULTS

The sample auto-correlations showed a decreasing trend with elapse of time, stable to repeated observations under the same conditions and sensitive to treatments.

CONCLUSION

The attribute of memory exists in some single channels as an intrinsic feature of them, independent of any extrinsic assumptions on missing observations due to limited time resolution.

Effects of Panax notoginseng saponins on receptor-operated Ca2+ channels in vascular smooth muscle

The effects of saponins of Panax notoginseng (PNGS) on the alpha-adrenoceptor agonists-induced contractile responses and Ca2+ movement were studied in dog mesenteric artery (MA) and saphenous vein (SV). PNGS reduced the contractions and the 45Ca influx (from 0.36 +/- 0.03 to 0.14 +/- 0.05 mumol.g-1 wet strip) induced by phenylephrine (Phe) without effect on KCl-induced contraction and 45Ca influx which were nearly completely inhibited by nifedipine 0.1 mumol.L-1. PNGS did not change the 45Ca efflux induced by Phe and the Kd value (from 0.76 +/- 0.04 to 0.72 +/- 0.15 nmol.L-1) for [3H]prazosin binding on the microsomal membrane isolated from MA. Our results indicate that PNGS selectively inhibits Ca2+ entry through receptor-operated Ca2+ channel.

Effects of direct lytic factors from southern Chinese cobra venom on Ca2+ movement in rabbit aorta strip

The purified direct lytic factors (DLF) from southern Chinese cobra (Naja naja atra) venom induced a contractile response in Ca(2+)-free Krebs' solution and a further increase in the tension following a subsequent addition of Ca2+ into bath. After depletion of intracellular Ca2+ pool by phenylephrine, DLF failed to induce any contractile response. In 45Ca2+ experiments, DLF increased both 45Ca2+ release and 45Ca2+ influx. Procaine 2 mmol.L-1 decreased the DLF induced 45Ca2+ release and 45Ca2+ influx by 67 +/- 23% and 46 +/- 32%, respectively. Nifedipine and verapamil 1 mmol.L-1 markedly inhibited the contractile response and the 45Ca2+ influx induced by DLF. These results suggest that DLF induces extracellular Ca2+ entry through voltage dependent Ca2+ channel and Ca2+ release from the intracellular Ca2+ pool which is sensitive to phenylephrine.

The relation between transmitter release and Ca2+ entry at the mouse motor nerve terminal: role of stochastic factors causing heterogeneity

The relation between quantal transmitter release and presynaptic Ca2+/Ba2+ entry at the mouse neuromuscular junction was studied, making use of the finding that in the presence of Ba2+ trains of nerve stimuli or brief nerve terminal depolarizations elicit "tails" of raised miniature end-plate potential frequency (fm) that reflect entry of Ba2+ per pulse, and hence effectiveness of pulses in opening Ca2+/Ba2+ channels; at the same time these pulses elicit end-plate potentials. With nerve stimulation in the presence of Ba2+ and Ca2+ and modulation of release by raised Mg2+ or bekanamycin, slopes of log quantal content (m) vs log apparent Ba2+ entry per pulse were close to 4, which is the same as the Hill coefficient for Ba2+ cooperativity derived from other data. With depolarizing pulses of varied intensity, however, similar plots gave slopes close to 2, with Ba2+ alone or in a mixture of Ca2+ and Ba2+. Thus, the relation between transmitter release and Ca2+ (or Ba2+) entry apparently depends upon how entry is varied; varying the numbers of channels opened is not the same as varying ion entry per channel. A mathematical model was developed to examine the consequences of heterogeneity of local Ca2+ (or Ba2+) between release sites, arising because of stochastic variation of number and time course of Ca2+ channels opened per site; the experimental results were consistent with this model. It was therefore concluded that release is normally governed by intracellular Ca2+ close to points of Ca2+ entry through channels; stochastic factors give rise to more release than if Ca2+ were homogeneously distributed. If Ca2+ channels are uniformly close to release sites the average number of channels opened per site per action potential may be as low as 4.

Cyclopiazonic acid causes endothelium-dependent relaxation in rat aorta

The effects of cyclopiazonic acid (CPA), a selective inhibitor of Ca(2+)-pump ATPase for endoplasmic reticulum (ER), on the contractility of rat aorta with and without intact endothelium were studied to investigate the possible involvement of endothelial ER Ca(2+)-pump in the release of endothelium-derived relaxing factor (EDRF), which is known to cause vascular relaxation or inhibition of phenylephrine (PE)-precontracted aorta. When added to the organ bath cumulatively, CPA concentration-dependently caused gradual development of contraction, which was much less in aortic rings with intact endothelium than in endothelium-denuded aortic rings. But CPA at low concentrations (1-3 mumol.L-1) induced vascular relaxation when added to PE (3 mumol.L-1)-precontracted aortic rings with intact endothelium, but not in denuded aortic rings. This relaxant effect of CPA is very similar to the effect of acetylcholine (ACh), which is well recognized to be mediated by the release of EDRF from the endothelium. NG-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, completely prevented the vascular relaxation induced by CPA or ACh and the inhibitory effect of L-NAME was partially reversed by L-arginine (L-Arg). Treatment of the aortic rings with nifedipine (Nif) 0.3 mumol.L-1 did not affect the relaxant effect of ACh or CPA on PE-induced contraction indicating that the Ca(2+)-entry to the endothelial cells as a result of receptor activation by ACh or ER Ca(2+)-pump inhibition by CPA was via channels other than L-type Ca2+ channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Tetrandrine is not a selective calcium channel blocker in vascular smooth muscle

The effects of tetrandrine (Tet) on the contractile properties of rat aortic ring preparations were studied to test the hypothesis that Tet is a Ca2+ antagonist acting on voltage-operated Ca2+ channels (VOC). The tests were performed on contractions induced by depolarizing concentrations of KCl and by alpha 1-adrenoceptor agonist, phenylephrine (Phe). These vascular effects of Tet were compared to those of nifedipine (Nif). We found that Tet behaved qualitatively similar to, but less potent than, Nif in that it inhibited KCl-induced contraction in a concentration-dependent fashion and its inhibitory effect was long-lasting. However, the effects on Phe-induced contraction of Tet was different from those of Nif in that the extracellular Ca(2+)-dependent contraction was inhibited by Tet, but not by Nif. Tet (60 mumol.L-1) completely inhibited the 45Ca2+ uptake induced by KCl and Phe in rat aortic muscle strips. When the aortic muscle contractile response was induced by addition of Ca2+ following depletion of intracellular stores by Phe in the presence of sarcoplasmic reticulum Ca(2+)-pump inhibitor, cyclopiazonic acid, Tet (60 mumol.L-1) was more effective than Nif 1 mumol.L-1 in inhibiting such a response to extracellularly added Ca2+. Furthermore, Tet, but not Nif, also significantly inhibited the contraction to Phe in Ca(2+)-free medium. Collectively, these results led us to conclude that Tet does not behave as a selective VOC blocker like Nif.

The effect of neonatal treatment of rats with nerve growth factor on the blood pressure and structure of the mesenteric arteries

Newborn male Wistar rats were treated with nerve growth factor daily by subcutaneous injection for 2 weeks, and control rats were treated with either cytochrome c or buffered saline. Average body weight of the treated animals was lower than that of the controls during the 2 weeks of treatment, but became similar to that of the controls thereafter. Tissue levels of norepinephrine were elevated in the brain, adrenal glands, mesenteric arteries, and vas deferens of the treated animals immediately after the treatment, but became similar in the three groups 2 weeks after the termination of the treatment. Blood pressure and heart rate were measured beginning at 4 weeks of age until 28 weeks, when the rats were sacrificed and the mesenteric arteries sampled for morphometric measurements of vessel wall dimensions. Pretreatment with nerve growth factor did not affect blood pressure, nor heart rate. Structural alteration of the three types of mesenteric arteries was also absent in the treated animals. We conclude that even though neonatal treatment of normal Wistar rats with nerve growth factor for 2 weeks induced an elevation of the norepinephrine levels in several tissues at the end of the treatment period, it was not sufficient to produce hypertension and structural alterations in the blood vessels.

Alpha 1-adrenoceptors mediate the responses to BHT-920 and rauwolscine in dog mesenteric artery after partial depolarization by KCl

In normal (5 mM KCl) HEPES buffer solution, BHT-920 and rauwloscine did not produce any contractile responses in dog mesenteric artery strips. However, when the preparation was bathed in 20 mM KCl HEPES buffer solution, BHT-920 and rauwloscine evoked significant contractile responses. These effects were markedly inhibited by parazosin which caused a parallel shift to the right of the concentration-response curve to BHT-920. In 45Ca uptake experiments carried out in the 20 mM KCl HEPES buffer solution BHT-920 and rauwolscine significantly increased 45Ca influxes which were reduced by prazosin. These results suggest that postsynaptic alpha 1-adrenoceptors in dog mesenteric artery mediate the contractile responses and the 45Ca influxes induced by BHT-920 and rauwloscine after partial depolarization by 20 mM KCl.

Contractile response of aorta to alpha 1-adrenergic stimulation in Ca(2+)-free medium is reduced in spontaneous hypertension

Vascular responses of aortic rings to alpha 1-adrenergic stimulation by phenylephrine (Phe) from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) were studied in Ca(2+)-containing medium and Ca(2+)-free medium plus 50 mumol/L EGTA. Although there was no difference in the sustained force development between SHR and WKY vessels in response to 100 mmol/L KCl or 10 mumol/L Phe in Ca(2+)-containing medium, the transient contractile response to 10 mumol/L Phe in Ca(2+)-free medium was substantially smaller in SHR compared to that in WKY. Subsequent addition of 2.5 mmol/L Ca2+ restored the sustained contractile response to a similar level in both SHR and WKY vessels. The transient contractile response to Phe in Ca(2+)-free medium containing EGTA, presumably due to the release of intracellular Ca2+, decreased progressively with preincubation time in Ca(2+)-free medium, indicating intracellular Ca2+ depletion. Such a temporal change of aortic response was more pronounced in SHR than in WKY. The subsequent response to Ca2+ repletion in the presence of Phe, on the other hand, increased progressively with Ca(2+)-depletion period and was higher in SHR than in WKY. The rate of relaxation after washout of Phe was slower in SHR aorta compared to WKY aorta. These results, together with our earlier findings, collectively suggest that the previous known deficiency in Ca2+ pumping mechanisms of vascular muscle microsomes leading to a reduced functional size of intracellular Ca2+ pool may account for the smaller contractile response of SHR aorta to alpha 1-adrenergic stimulation in Ca(2+)-free medium and the slower rate of relaxation.

Alpha-adrenoceptors in vascular smooth muscle: all is not well

Studies of binding interactions and contractile responses of vascular muscles at alpha 1- and alpha 2-adrenoceptors revealed the following. (1) Agonists at alpha 1- and alpha 2-adrenoceptors may achieve selectivity by virtue of different efficacies despite similar affinities at the two receptors as well as by differing affinities. This implies that their potencies in binding studies may not correlate with potencies in response and that an agonist may produce positive or negative interactions by occupying both alpha 1- and alpha 2-receptors. (2) Agonists at alpha 2-adrenoceptors have the ability in some vascular muscles to release internal Ca2+ (implying an inositol triphosphate mechanism) as well as open Ca2+ channels. However, their contractile abilities are not closely related to function of Na+/H+ or Na+/Ca2+ exchange sites. Amiloride derivatives probably inhibit contractile effects of alpha-agonists and K+ elevation by an action at sites distal to the receptor or Ca channels. (3) The failure of alpha 2-agonists to contract arteries in vitro is not related to the absence of these receptors but most likely to their uncoupling from contractile responses, possibly owing to changes related to the in vitro condition (loss of modulating endogenous substances present in vivo such as angiotensin II or endothelins or to changed physical conditions such as may alter function of stretch-activated channels).

Evidence against the role of alpha 1-adrenoceptor reserve in buffering the inhibitory effect of nifedipine on the contractility of canine vascular smooth muscle

The relationship between the postsynaptic alpha 1-adrenoceptor reserve and the sensitivity of vasoconstriction induced by alpha-adrenoceptor agonists to the dihydropyridine Ca2+ entry blocker nifedipine was investigated in isolated muscle strips of dog mesenteric artery (DMA) and saphenous vein (DSV). The amplitudes of the contractile responses of DMA induced by phenylephrine were the same as those in DSV in the presence and in the absence of extracellular Ca2+. The use of 3 x 10(-9) M phenoxybenzamine to irreversibly block the alpha 1-adrenoceptors revealed a marked difference in the size of the alpha 1-adrenoceptor reserve between DMA (40%) and DSV (7%). In spite of a larger receptor reserve, the contractile responses induced by phenylephrine in DMA were more sensitive to nifedipine compared with those in DSV. These results suggest that the postsynaptic alpha 1-adrenoceptor reserve in vascular smooth muscle, at least in DMA and DSV, does not play an important role in buffering the inhibitory effect of nifedipine on the contractile response to a full agonist of alpha 1-adrenoceptors. Other factors, such as the difference in the membrane depolarizing effect, the ability to utilize intracellular Ca2+ for contraction, and the possible existence of alpha 1-adrenoceptor subtypes, may contribute to the different inhibitory effects of nifedipine on these blood vessels.

Does in vitro activation of postsynaptic alpha 2-adrenoceptor utilize intracellular Ca2+ for contraction in dog saphenous vein?

Dog saphenous vein spiral strips were employed to determine whether an intracellular source of Ca2+ is used for contraction upon activation of the alpha 2-adrenoceptor by B-HT 920 in Ca2+-free Krebs solution containing 50 microM EGTA. The studies were carried out in parallel with the activation of the alpha 1-adrenoceptor by phenylephrine (Phe) under the condition that B-HT 920 (10(-5) M) and Phe (2 x 10(-6) M) gave rise to a similar level of responses in Ca2+-containing Krebs solution. A similar level of responses to these agonists at equieffective concentrations in Ca2+-free medium were also observed. Such responses to Phe and B-HT 920 were inhibited by 10(-7) M rauwolscine and 10(-7) M prazosin, respectively, and were not affected by 10(-7) M nifedipine or 5 mM Mn2+. The responses to B-HT 920 (10(-5) M) and submaximal concentration of Phe (2 x 10(-6) M) in Ca2+-free medium were additive. However, if the vascular strips were first contracted maximally with 10(-4) M Phe in Ca2+-free medium to deplete the intracellular Ca store, subsequent addition of B-HT 920 failed to induce additional response. Our results strongly suggest that activation of alpha 2-adrenoceptor in dog saphenous vein in Ca2+-free medium indeed utilizes intracellular Ca2+ for contraction. We also found that the failure of earlier studies to demonstrate the contractile effects of B-HT 920 in dog saphenous vein was due to experimental artifacts derived from the use of high concentration of EGTA and artificial pH-buffering reagent.

Abnormal contractile response of aortas from spontaneously hypertensive rats to Ca2+ after depletion of Ca2+ in Ca2+-free medium

Vascular responses of aortic rings from spontaneously hypertensive rats (SHR) were compared to those of the normotensive Wistar-Kyoto rats (WKY) in three sets of experimental protocols. The responses to cumulative doses of KCl indicated that SHR aortic rings were hyperresponsive to low but not high doses of KCl compared to WKY aortic rings. After Ca depletion by prolonged incubation of the rat aortic rings with Ca2+-free, EGTA containing solution, Ca repletion resulted in contraction. The magnitude of such a contraction was dependent on the period of Ca depletion and was highly sensitive to dihydropyridine Ca channel blocker, nifedipine. Although the Ca-depleted aortic rings eventually developed to the same level of maximum tension development upon Ca repletion, it took a considerably shorter period of Ca depletion for SHR than for WKY aortic rings to reach the maximum contraction upon Ca repletion. Our findings support the view that cell membranes of vascular smooth muscle in hypertension are more excitable and more susceptible to membrane destabilization by Ca removal.

The effects of EGTA on vascular smooth muscle contractility in calcium-free medium

The effect of EGTA, commonly present in Ca2+-free physiological saline solution, on the contractile responses induced by Ca2+ and phenylephrine was studied in dog mesenteric arteries and aortas of rats and rabbits. EGTA substantially enhanced the contractile responses of these vascular strips or rings to added Ca2+ after a prolonged preincubation period in the Ca2+-free medium. The maximal level of the enhanced contractile responses was independent of EGTA concentration, but the rate of the maximal responses was faster at higher EGTA concentration, presumably as a result of faster removal of intracellular Ca2+. Such a Ca2+-induced response was sensitive to the Ca2+ antagonist, nifedipine. EGTA present at low concentrations (50 and 400 microM) in Ca2+-free medium also inhibited the phenylephrine-induced contractile response more prominently for the longer preincubation periods of the vascular tissues in Ca2+-free medium. Our results suggest that EGTA, even when added at low concentrations to the vascular smooth muscle for a sufficiently long period in Ca2+-free medium, may cause destabilization of the cell membranes leading to increased permeability to subsequently added Ca2+. EGTA may also remove the superficially bound Ca2+ and subsequently reduce the intracellular Ca2+ pool via extraction of the intracellular Ca2+ at the cell membrane surfaces.

Interactions of saponin with microsomal membranes isolated from vascular smooth muscle

The effects of the plant glycosides extract, saponin, on various biochemical properties of microsomal fractions isolated from dog aortae and mesenteric arteries were investigated. These properties include binding and transport of Ca2+, ouabain-sensitive K+ activated p-nitrophenyl phosphatase (hereafter termed K+-pNPPase) and binding of radiolabelled antagonists to adrenoceptors. We found that saponin inhibited both Ca2+ binding and transport by the vascular muscle microsomes in a dose-dependent manner, but it caused marked enhancement of the K+-pNPPase activity. Saponin only slightly reduced the Bmax, but not the Kd of [125I]-iodocyanopindolol binding to the beta-adrenoceptors of the dog mesenteric artery microsomes. A similar finding on the [3H]-prazosin binding to the alpha 1-adrenoceptor in dog aortic microsomes was also observed. Our findings are consistent with the "skinning" action of saponin on the smooth muscle and provide direct evidence that saponin does not attenuate the recognition properties of the adrenoceptors in the cell membranes.

Single Ca2+ entry and transmitter release systems at the neuromuscular synapse

The possibility that there exists more than one voltage-gated Ca2+ channel system subserving quantal release of neurotransmitter at nerve endings was examined by measuring the sensitivity of quantal release to agents that block Ca2+ or Ba2+ entry, namely Cd2+, Mg2+, neomycin, and bekanamycin. The results show equal effectiveness vs. release evoked by presynaptic action potentials, brief intense presynaptic depolarizations, or prolonged relatively mild depolarizations, from which it is concluded that the same channel system is involved in each case. In the presence of Ba2+ and no Ca2+, there occur essentially normal (but small) endplate potentials (epps), while in the presence of Ba2+ and Ca2+ epp amplitude and frequency of miniature epps co-modulate with stimulation frequency in a manner which corresponds to a residual Ba2+ model for augmentation. It is therefore also concluded that a single transmitter release system is responsible for normal phasic release and the asynchronous release that is mediated by Ba2+.

Multiple potassium conductances at the mammalian motor nerve terminal

The possibility that multiple K+ conductances are present in mammalian motor nerve terminals was investigated by measuring the differential effects of tetraethylammonium (TEA) and 4-aminopyridine (4-AP) on transmitter release and on nerve terminal excitability in mouse phrenic nerve-diaphram preparations. Neither 4-AP nor TEA alter the spontaneous frequency of miniature end-plate potentials (fmepp) and therefore evidently do not affect calcium channels directly. Both 4-AP and TEA increased the quantal content of end-plate potentials (epps) evoked by nerve stimulation but the effects were not mutually exclusive; TEA continued to act in the presence of a maximally effective concentration of 4-AP. The increase in transmitter release evoked by focal polarisation of the terminal was not affected by 4-AP, whereas TEA exerted an effect consistent with a reduction in membrane conductance. Similarly, threshold for nerve terminal action potential generation was not affected by 4-AP, but TEA caused a reduction in threshold and alteration of the 'accommodation curve' indicative of a reduction of membrane conductance. Under conditions where one would predict no contribution of calcium K+ conductance, i.e., when release was evoked by Ba2+ in the absence of Ca2+, the different and non-competing effects of TEA and 4-AP were still apparent. It is concluded, therefore, that the motor nerve terminal possesses at least two K+ conductances, not including calcium activated gK, which may be distinguished pharmacologically.

Multiple actions of cadmium on transmitter release at the mouse neuromuscular junction

The action of cadmium ions on transmitter release was studied at the neuromuscular junction in mouse diaphragm. In the presence of raised K+, Cd2+ caused a parallel shift to the right of the graph of transmitter release rate (frequency of miniature end-plate potentials, fmepp) versus log [Ca2+], with no change in maximum or slope, indicating a competitive mode of action of Cd2+. The apparent dissociation constant for Cd2+ was 3 microM. In calcium-free solutions containing 15 mM K+, Cd2+ caused a rise in the fmepp, which subsequently slowly declined despite the continued presence of Cd2+. The rise in fmepp caused by Cd2+ could be interrupted, but not reversed, by washing out the Cd2+ with EDTA. Exposure of the preparation to 100 microM Cd2+ for 15 min or more resulted in a raised fmepp that persisted despite the removal of Cd2+ and exposure to 200 microM EDTA. Following such treatment, the graph of fmepp versus log [Ca2+] continued to be shifted to the right. The interaction of Ca2+ with the residual effect of Cd2+ indicates that Cd2+, in addition to its action to block Ca2+ entry into the terminal, may act as a competitor and perhaps as a partial agonist at intracellular sites that normally bind Ca2+ and govern transmitter release. If this is the case, then it must be supposed that, in raised K+, quantal release of transmitter represents intermittent intense activation of release sites with local high levels of Ca2+ rather than continuous low level activation.