Expression and localization of angiotensin subtype receptor proteins in the hypertensive rat heart

The cellular localization of the AT(2) receptor and the regulation of its expression in hypertrophied left ventricle are not well known. We compared the expression of the cardiac AT(1) and AT(2) receptor in spontaneously hypertensive rats/Izumo strain (SHR/Izm) and Wistar Kyoto rats/Izumo strain (WKY/Izm), ages 4, 12, and 20 wk, by means of immunohistochemistry and Western blot analysis. In SHR/Izm, compared with WKY/Izm, blood pressure (161 +/- 2 vs. 120 +/- 2 mmHg at 12 wk, P </= 0.01, and 199 +/- 3 vs. 123 +/- 3 mmHg at 20 wk, P </= 0.01) and heart-to-body weight ratio (3.76 +/- 0.07 vs. 3.06 +/- 0.06 mg/g at 12 wk, P </= 0.01, and 3.90 +/- 0.08 vs. 3.01 +/- 0.12 mg/g at 20 wk, P </= 0.01) were significantly elevated. There was no difference in these values between the two strains at 4 wk of age. Histologically, 20-wk-old SHR/Izm demonstrated myocardial hypertrophy, a thickening of the smooth muscle layer of the intracardiac arteries, and perivascular fibrosis. By immunohistochemistry, the AT(2) receptor was localized to cardiomyocytes and vascular endothelial cells, but not in the vascular smooth muscle cells. No major AT(2) receptor signal was observed in perivascular fibrosis at any age in either strain of rats. No difference was detected in this localization between the two strains. By Western blotting, a single 44-kDa band for the AT(2) receptor and a single 60-kDa band for the AT(1) receptor were detected in ventricles from both strains of rats at all ages. Densitometric analysis demonstrated that the AT(2) receptor 44-kDa band was decreased by 20% at 12 wk and 32% at 20 wk (P < 0.01) in SHR/Izm compared with WKY/Izm. The intensity of the AT(1) receptor 60-kDa band was increased by 57% in 20-wk-old SHR/Izm compared with WKY/Izm (P < 0.05). There was no significant difference in the intensity of the 44- or 60-kDa bands in 4-wk-old animals of either strain. We demonstrated a decrease in the AT(2) receptor and an increase in the AT(1) receptor protein with no change in their localizations in hypertrophied left ventricular myocytes of SHR/Izm.

Abnormal magnesium status in patients with cardiovascular diseases

To investigate magnesium status in patients with cardiovascular diseases and in those presenting high factors for these diseases, we measured the concentrations of serum total Mg, serum ionized Mg and intra-erythrocyte Mg. Mg is an important cofactor for many enzymes, especially those involved in phosphate transfer reactions. Mg deficiency has been shown to be associated with fatal cardiovascular diseases, as well as with risk factors for these diseases. Only measurement of the serum concentration of total Mg is routinely available, but ionized Mg is the physiologically active component. Furthermore, most of the body's Mg is present in the intracellular space. Subjects included patients with ischaemic heart disease (n=80), cardiac arrhythmia (n=60), diabetes mellitus (n=36), essential hypertension (n=194) and hypercholesterolaemia (n=60). The same measurements were made in healthy controls (30 men and 26 women; mean age 58+/-11 years). The serum ionized Mg concentration was measured with a selective ion electrode. The intra-erythrocyte Mg concentration was measured by atomic absorption. No gender difference was found for any Mg parameter, nor was age related to any Mg parameter. The serum albumin concentration was positively correlated only with the serum total Mg concentration. Although the serum total Mg concentration was similar in all groups, patients with diabetes mellitus and arrhythmia had lower serum levels of ionized Mg. Patients with essential hypertension exhibited higher intra-erythrocyte Mg concentrations than the healthy controls. Thus the measurement of serum total Mg concentration may obscure the presence of extracellular Mg deficiency in patients with arrhythmia and diabetes mellitus. Furthermore, the intracellular accumulation of Mg does not support the hypothesis of Mg deficiency in patients with essential hypertension.

[Expired nitric oxide concentration derived from nasal cavity and that derived from airway and lung in Japanese cedar pollinosis]

AIM

Japanese cedar pollinosis (Type I allergy to Japanese cedar pollen) shows a high incidence in spring in Japan, demonstrating symptoms such as pituita, rhinostenosis, lacrimation and sometimes pharyngeal pain. The following study investigated whether expired nitric oxide (NO) concentration is increased in Japanese cedar pollinosis, and whether expired NO concentration can be used to discriminate from cold syndrome which symptoms are similar to Japanese cedar pollinosis.

SUBJECTS AND METHODS

In 20 healthy subjects, 20 patients with Japanese cedar pollinosis and 20 patients with cold syndrome, expired NO concentrations derived from nasal cavity and those derived from airway and lung were measured. Expired NO concentrations derived from nasal cavity and those derived from airway and lung were compared among the groups.

RESULTS

In patients with Japanese cedar pollinosis expired NO concentrations derived from nasal cavity and those derived from airway and lung markedly increased. In patients with cold syndrome there were no significant increases in these concentrations.

DISCUSSION

It is considered that expired NO concentration is useful for discriminating Japanese cedar pollinosis from cold syndrome. It seems interesting that not only expired NO concentrations derived from nasal cavity but also those derived from airway and lung were clevated. Generalized airway inflammation may be present, even without clinical asthma, in patients with Japanese cedar pollinosis.

[The future of clinical laboratory database management system]

To assess the present status of the clinical laboratory database management system, the difference between the Clinical Laboratory Information System and Clinical Laboratory System was explained in this study. Although three kinds of database management systems (DBMS) were shown including the relational model, tree model and network model, the relational model was found to be the best DBMS for the clinical laboratory database based on our experience and developments of some clinical laboratory expert systems. As a future clinical laboratory database management system, the IC card system connected to an automatic chemical analyzer was proposed for personal health data management and a microscope/video system was proposed for dynamic data management of leukocytes or bacteria.

[Significance of area under the flow volume curve--useful index of bronchial asthma]

Some studies have reported that area under the flow volume curve (AUFVC) can be an index of pulmonary function. However, the significance of AUFVC remains to be clarified. We have clarified that AUFVC reflects the momentum of expired air. Size of flow volume curve (= AUFVC) has been commonly recognized to be changeable visually in patients with asthma. To clarify whether size of flow volume curve (= AUFVC) is a useful index of the course of bronchial asthma, we compared the rate of improvement forced expiratory volume in 1 second (FEV1.0), peak expiratory flow rate (PEFR) or forced vital capacity (FVC) to the rate of improvement in AUFVC after admission in 20 patients with bronchial asthma. The rate of improvement in AUFVC positively correlated with the rate of improvement in FEV1.0, PEFR or FVC. AUFVC demonstrated more marked improvement than other indices. Since AUFVC reflects the momentum of expired air, bronchial asthma's patients could understand visually that the momentum of expired air decreased due to airway stenosis by presenting flow volume curve. Therefore, visual size of flow volume curve helped patients with asthma to understand the condition of asthma. Size of flow volume curve (AUFVC) may be useful index of the course of bronchial asthma.

[Magnesium (Mg) status in patients with cardiovascular diseases]

Mg is the fourth most abundant total cation in the human body and the second most abundant intracellular cation. Moreover, Mg is an important cofactor for many enzymes especially those involved in phosphate transfer reactions. Mg is therefore essential in the regulation of the metabolism of other ions and cellular functions. Mg deficiency has been shown to be associated with fatal cardiovascular diseases such as cardiac arrhythmias and coronary heart disease, as well as with risk factors for these diseases, such as hypertension, and diabetes mellitus. Clinical evaluation of Mg status has been limited by the lack of suitable technology for measuring this cation. Although the measurement of serum total Mg is routinely available, ionized Mg is physiologically active. Furthermore, most of the body's Mg is present in the intracellular space. Our findings showed that serum total Mg was similar in all groups, but patients with arrhythmias and diabetes mellitus revealed lower levels of serum ionized Mg. On the other hand, patients with essential hypertension exhibited higher intraerythrocyte Mg concentrations than healthy controls. The measurement of serum total Mg may obscure the diagnosis of an abnormality in Mg metabolism in patients with arrhythmias and diabetes mellitus. Furthermore, the intracellular accumulation of Mg does not support the hypothesis of Mg deficiency in patients with essential hypertension.

[The present and future of the pulmonary function tests. The relationship between respiratory and non-respiratory function]

Pulmonary function is classified as respiratory and non-respiratory function. Respiratory pulmonary function involves exchange of O2 and CO2 gas at alveolar units in the lung and non-respiratory pulmonary function concerns metabolism of enzymes, hormones, surfactants vaso-active substances and immunological factors in the lung. The purpose of this study was to examine the relationship between respiratory and non-respiratory function using our newly developed expired NO gas continuous analytic method and the calculation method of ventilatory energy of the lung. Furthermore, we analyzed the relationship between arterial blood O2 pressure (PaO2) and mitochondrial function.

Effect of L-arginine infusion on systemic and renal hemodynamics in hypertensive patients

This study was designed to compare the renal endothelial function in patients with essential hypertension and normal renal function with that in hypertensive patients with renal insufficiency. We studied the effects of L-arginine (500 mg/kg intravenously over 30 min) on renal hemodynamics in 30 normotensive control subjects, 32 patients with mild to moderate essential hypertension who had normal renal function, and seven hypertensive patients with renal insufficiency who had a serum creatinine concentration >2.0 mg/mL and a glomerular filtration rate <50 mL/min/1.48 m2. L-Arginine infusion similarly reduced the mean blood pressure between the three groups (normotensive: -9.7% +/- 0.7%, hypertensives with normal renal function: -10.2% +/- 0.8%, and hypertensives with renal insufficiency: -8.2% +/- 1.3%). The L-arginine-induced decrease in renal vascular resistance was smaller in essential hypertensive patients than in normotensive subjects (-11.0% +/- 2.2 v -19.8% +/- 2.1%, P <.05). However, L-arginine had no effect on the renal vascular resistance in hypertensive patients with renal insufficiency (1.6% +/- 4.8%). Urine nitrite/nitrate levels in response to L-arginine significantly increased in the three groups in the following order: patients with renal insufficiency (47% +/- 15%), essential hypertensive patients (87% +/- 10%), and normotensive subjects (129% +/- 12%). The glomerular filtration rate was unaffected by L-arginine in normotensive and essential hypertensive patients (3.1% +/- 2.4% and 4.2% +/- 2.5%), but significantly decreased in hypertensive patients with renal insufficiency (-13.7% +/- 6.1%). These findings suggest that the ability of the L-arginine-nitric oxide-cGMP pathway to relax the renal vascular tone may be impaired in essential hypertensive patients and more markedly blunted in hypertensive patients with renal insufficiency, in parallel with increasing serum creatinine concentrations.

[A case of cervical-mediastinal lymph node tuberculosis progressed to pulmonary lesion through a bronchial fistula]

The patient was a 25-year-old man who had been admitted to a local hospital due to fever and trachelophyma. Tubercle bacillus was detected in pus culture obtained by biopsy of the trachelophyma, but not in sputum culture. Because combined therapy with 3 antituberculous drugs (RFP, INH and SM) failed to reduce the fever or drainage from the biopsy region, the patient was transferred to our hospital. Chest X-ray films taken on admission revealed dilatation of the superior mediastinal shadow; chest CT images revealed cervical and mediastinal lymphadenopathy and an anterior mediastinal abscess, but no pulmonary lesion. About 2 months after admission, cough developed and Gaffky type 2 was detected in the patients sputum. Bronchoscopy and bronchography revealed a bronchomediastinal fistula. Forty days after the onset of cough, reticulogranular shadows were observed in the right upper lobe on chest X-ray films, and a diffuse centrilobular lesion was observed in the right upper lobe on chest CT images. From these clinical observations, the patient was given a diagnosis of cervical-mediastinal lymph node tuberculosis, which had progressed to pulmonary lesion through a bronchial fistula due to lymphadenitis.

Cloning and characterization of a novel zinc finger protein that associates with nuclear matrix

We have recently reported that the nuclei of B16 melanoma cells are intensely stained with anti-rat vitronectin (Vn) antibody, which reacts with both mouse and rat Vn. In the present study, we characterized the protein immunoreactive with the antibody using NIH3T3 cells, whose nuclei were also stained with the antibody. Western blot analysis showed that a protein with an approximate molecular weight of 75 kDa (p75), which was distinct from Vn, existed in the nuclear fraction, and, more specifically, in the nuclear matrix fraction, of NIH3T3 cells. Screening of an NIH3T3 cDNA library resulted in the isolation of a nearly full-length cDNA clone encoding p75. A database search revealed that the cDNA represents a novel gene. The deduced amino acid sequence showed that the protein is 580 amino acids long and contains two C2H2-type zinc finger motifs and glutamic acid-rich domains in the C-terminal region. When a fusion protein of green fluorescence protein and p75 was expressed in NIH3T3 cells, fluorescence was preferentially observed in the nuclei, demonstrating that the protein has a nuclear localization signal. The p75 protein, termed ZAN75, exhibited DNA-binding activity in a zinc-dependent manner. Southern blot analysis demonstrated that the ZAN75 gene exists in a single copy in the mouse genome and that a closely related gene is also present in chicken, rat, and human. Northern blot analysis showed that the ZAN75 gene is ubiquitously expressed in adult mouse tissues. In the cell cycle of NIH3T3 cells, expression was low in the G0/G1 phase, increased during the G1 phase, and persisted during the S and G2/M phases, suggesting that ZAN75 plays a role in regulating cell growth.

[A mild case of acute eosinophilic pneumonia]

We encountered a mild case of acute eosinophilic pneumonia in a 24-year-old man who developed symptoms once he started smoking. Bronchoalveolar lavage revealed eosinophilia. Chest computed tomography revealed a small amount of bilateral pleural effusion and multicentric panacinar shadows with peripheral ground-glass opacities. During the clinical course, the patient suffered only cough and fever, which subsided in 13 days without the administration of steroids. Although the clinical course in this case resembled that of simple pulmonary eosinophilia, we diagnosed it as a mild case of acute eosinophilic pneumonia because pleural effusion rarely accompanies simple pulmonary eosinophilia, symptoms developed when the patient began smoking, and interstitial involvement was suggested by bilateral effusion and ground-glass opacity. We look forward to the establishment of the disease concept of acute eosinophilic pneumonia, including mild cases, and a classification system for eosinophilic lung diseases, including acute eosinophilic pneumonia.

Angiotensin-converting enzyme inhibition, but not calcium antagonism, improves a response of the renal vasculature to L-arginine in patients with essential hypertension

Endothelial function has been shown to be impaired in patients with essential hypertension. The purpose of the present study was to determine whether antihypertensive drug therapy improves impaired endothelium-dependent renal vasorelaxation in essential hypertensive patients without atherosclerosis. We evaluated the effects of intravenous infusion of L-arginine (500 mg/kg given over 30 minutes) on systemic and renal hemodynamics in 27 patients with mild to moderate essential hypertension who were randomly assigned to treatment with either the angiotensin-converting enzyme inhibitor imidapril or the calcium antagonist amlodipine for 12 weeks in a double-blind fashion. After the 12 weeks, the decrease in blood pressure was similar in the imidapril (n=14) and amlodipine (n=13) groups. The increase in renal plasma flow was also similar in both groups. L-Arginine-induced renovascular relaxation was increased by imidapril (renal plasma flow, 9.6+/-5.1% to 14.4+/-7.4%; renal vascular resistance, -10.4+/-8.1% to -16.7+/-9.2%, P<0.05, respectively) but not by amlodipine. Urinary excretion of nitrite/nitrate in response to L-arginine was significantly increased by imidapril (90+/-29% to 134+/-63%, P<0.05) but remained unchanged by amlodipine. These findings suggest that angiotensin-converting enzyme inhibition improves the impaired endothelium-dependent renovascular relaxation in patients with essential hypertension due to the increase in nitric oxide production and that the reduction in blood pressure with a calcium antagonist does not play a major role in the potentiation of L-arginine/nitric oxide-mediated effects.

Effect of 17beta-estradiol on inhibition of platelet aggregation in vitro is mediated by an increase in NO synthesis

The low prevalence of coronary heart disease in premenopausal women and its increase after menopause are well established. Although estrogen is thought to play a role in protecting the vasculature, the mechanism has not been fully clarified. The contribution of platelets to atherosclerotic cardiovascular diseases is well recognized. The present study focused on the still-controversial effect of estrogen on platelet function. We investigated the in vitro effects of estrogen on human platelets, including their aggregation, Ca2+ metabolism, the synthesis of cyclic nucleotides, and NO (nitrite/nitrate) synthesis after stimulation with thrombin or ADP. Pretreatment of platelets with 17beta-estradiol reduced the platelet aggregation induced by thrombin or ADP, whereas 17alpha-estradiol had no effect. 17Beta-estradiol accelerated the recovery of [Ca2+]i after the agonist-induced peak and reduced the area under the curve of accumulated platelet [Ca2+]i but did not alter the baseline [Ca2+]i, Ca2+ influx induced by thrombin or ADP, the release of Ca2+ from internal stores, or the size of internal Ca2+ stores. Pretreatment of platelets with 17beta-estradiol had no effect on the intracellular concentration of cAMP but increased that of cGMP in agonist-stimulated platelets. Additionally, 17beta-estradiol increased the platelet concentration of nitrite/nitrate in a dose-dependent manner. These effects of 17beta-estradiol on platelet aggregation, Ca2+ metabolism, and NO synthesis were abolished by exposure to N(G)-monomethyl-L-arginine, an NO synthesis inhibitor. These results suggest that 17beta-estradiol plays an important role in inhibiting platelet aggregation by promoting Ca2+ extrusion or reuptake activity that is dependent on the production of cGMP by increasing NO synthesis.

DD genotype of the angiotensin I-converting enzyme gene is a risk factor for early onset of essential hypertension in Japanese patients

Although angiotensin-converting enzyme (ACE) plays an important role in blood pressure regulation, no relationship between the insertion/deletion (I/D) polymorphism of the ACE gene and essential hypertension has been observed. However, as the pathogenesis and genetic background of essential hypertension are heterogeneous, we investigated whether the ACE gene is a marker of subgroups of patients with essential hypertension. A group of 178 patients with essential hypertension (90 men/88 women; 53 +/- 13 years of age, mean age +/- SD ) and 101 normotensive control subjects (54 men/47 women; 51 +/- 14 years of age, mean age +/- SD ) were included in the study. The allele frequencies of the two groups were similar. There were no differences in age, blood pressure, retinopathy grade, presence of proteinuria, or resting plasma renin activity (PRA) among the hypertensive patients with the II, ID, and DD genotypes. However, the age of onset of hypertension of patients with the DD genotype was lower (p < 20.05) and their left ventricular mass index was higher (p < 2 0.05) than those in patients with the non-DD genotype. These data suggest that the I/D polymorphism of the ACE gene is associated with an early onset of hypertension and left ventricular hypertrophy in Japanese patients with essential hypertension.

[Measurement of expired nitric oxide concentration]

Much interest has been focused on standardization of measurement of expired nitric oxide (NO) concentration. The aim of this study was establish a simple measurement of expired NO concentration.

SUBJECTS AND METHODS

This study included 5 healthy male adults. To clarify whether NO is excreted in expired air constantly, its concentrations were measured while changing the flow rate. To examine the influence of NO derived from the nasal cavity, we compared expired No concentrations sampled from the month with those sampled from the endotracheal tube inserted to the trachea at a constant flow rate serially.

RESULTS

Expired NO concentrations decreased in inverse with the flow rate. No may be serially excreted in expired air. When serial changes of expired No concentrations sampled from the mouth were examined, its NO concentration initially reached a peak, then showed a plateau. Serial changes of those sampled from the endotracheal tube showed only a plateau. Plateau levels were not different between the two kinds. Therefore the peak values may have been influenced by NO derived from the nose that fell in the trachea by inspiration. Plateau values appeared to represent airway and lung-derived NO.

CONCLUSIONS

A simple measurement of expired NO concentration should be sampled from the mouth at a constant flow rate serially. Evaluating plateau values is appropriate for expired NO concentration.

Activation of platelets in bronchial asthma

STUDY OBJECTIVES

To investigate whether platelets are activated in asthmatics with increased release of preformed mediators and to investigate the influence of oral administration of theophylline on them.

DESIGN

Comparison of the intracellular free calcium concentration ([Ca2+]i) in platelets as an indicator of platelet activation, CD62P expression on platelets, and the chemokine regulated upon activation in normal T cells expressed and presumably secreted (RANTES) level in platelet-rich buffer supernatants between asthmatics and normal subjects.

SETTING

The respiratory outpatient clinics, Hiroshima University, Japan.

PARTICIPANTS

Twenty-five normal volunteers, 19 asthmatics taking no oral drugs associated with asthma treatment (group A), and 18 asthmatics taking oral theophylline (group B).

MEASUREMENTS AND RESULTS

While the resting [Ca2+]is in platelets were similar among the three groups, the [Ca2+]is in group A were significantly higher than those in normal subjects (p<0.05) and group B (p<0.01) after thrombin or 9,11-epithia-11,12-methano-thromboxane A2 (STA2) stimulation in the absence of external Ca2+. The CD62P expression level and RANTES level in group A after STA2 stimulation were significantly higher than those in normal subjects and group B (p<0.05).

CONCLUSIONS

We conclude that agonist-mediated activation of platelets is augmented in asthmatics resulting in enhanced release of chemokine such as RANTES, which could be suppressed by oral administration of theophylline.

Increased cytosolic free Mg2+ and Ca2+ in platelets of patients with vasospastic angina

This study was designed to test the hypothesis that the cellular metabolism of Ca2+ and Mg2+, which is important in platelet function, is abnormal in the platelets of patients with vasospastic angina. Cytosolic free Mg2+ concentration ([Mg2+]i) and Ca2+ handling were determined in the platelets of 24 patients with vasospastic angina and 24 control subjects by use of mag-fura 2 and fura 2. Platelet aggregation was also examined. Basal [Mg2+]i and cytosolic free Ca2+ concentration ([Ca2+]i) in platelets were significantly higher in patients with vasospastic angina than in control subjects. The amplitude of the [Ca2+]i transient induced by thrombin (0.03-1.0 U/ml) was significantly increased in the presence, but not in the absence, of extracellular Ca2+ in patients with vasospastic angina, as compared with controls. Therefore, the influx of Ca2+ across the plasma membrane may be accelerated in vasospastic angina. Thrombin (0.1-1.0 U/ml)-induced maximum aggregation response was significantly greater in patients with vasospastic angina than in controls. Results suggest that increased [Mg2+]i and altered Ca2+ handling by platelets may be associated with coronary vasospasm.

Characterization of the integrin alpha(v) gene promoter in mice

To characterize a promoter for integrin alpha(v) in mice, we cloned a 5'-flanking region of the mouse integrin alpha(v) gene. The nucleotide sequence of the promoter region lacks both TATA or CCAAT boxes, and has the consensus sequence for Sp1, Ets, AP-2 and GATA-1. The transcription initiation site was mapped as 287 base pairs (bp) upstream from the translation initiation site by primer extension analysis. To analyze the promoter activity of the integrin alpha(v) gene, the successive 5'-deletions which were cloned upstream of the luciferase reporter gene were transfected into mouse melanoma B16F10 cells with high metastatic properties. The luciferase assay reveals that a region (positions -108 to +22) has important cis-acting elements for the promoter activity. Further, three distinct protein-DNA complexes in the promoter region were detected in a gel shift assay using nuclear extracts from B16F10 cells. To identify positions where the complexes are formed, the promoter region (positions -108 to +97) was subjected to DNaseI footprinting analysis. The analysis showed that a 17 bp-element (positions -31 to -15) interacts with putative transcription factors. Deletion of the 17 bp-element from the promoter resulted in a reduction of about 80% in the promoter activity when compared with the wild type promoter, and a gel shift assay using the deleted mutant of the promoter showed only one protein-DNA complex. These results reveal that the 17 bp-element contains cis-acting elements, and plays an important role in the transcription initiation of the integrin alpha(v) gene.

[The present and future of clinical physiologic tests]

The symposium on clinical physiologic tests was designed in the 44th congress of all central laboratory divisions of national university hospitals at 28, 29 May in 1997. The title of symposium was "the present and future of clinical physiologic tests" which was named by professor M. Itoh. Four symposists were nominated among the specialists on clinical physiologic tests of members of above congress. Professor M. Itoh and Professor H. Kawaguchi spoke about Erectric Cardio Graphy (ECG) and main heart function tests and Professor M. Kambe spoke about pulmonary function tests and Professor M. Okada spoke about the using methods of clinical physiologic test data in remote and distant medicine. The special feature of clinical laboratory division in Japanese large hospitals is that has clinical physiologic tests part and the clinical laboratory division of hospitals in foreign countries has no clinical physiologic tests part. So, we expect more development of clinical physiologic tests part in nearly future.

Nonadrenergic, noncholinergic inhibitory innervation in the longitudinal muscle of the rabbit portal vein

1. We examined whether nitric oxide (NO) and ATP take part in inhibitory nonadrenergic, noncholinergic (NANC) neurotransmission in the portal vein of Japanese White rabbits. Longitudinal strips of the vein were suspended in organ baths containing Krebs bicarbonate solution. Preparations relaxed in response to electrical field stimulation (EFS) (25 V, 0.5 msec in duration, 1-50 Hz) and exogenous ATP (1-300 microM) after contraction was induced with 10 microM ergotamine in the presence of 3 microM guanethidine and 0.1 microM atropine. 2. The relaxation response to EFS was abolished by addition of 100 microM NG-nitro-L-arginine, an NO synthase inhibitor. This abolition was partly reversed by 10 mM L-arginine, a substrate for NO synthase. 3. The relaxation response to exogenous ATP was significantly inhibited by 1 mM suramin, a P2X- and P2Y-purinoceptor antagonist, whereas relaxation response to EFS was not inhibited by 1 mM suramin. 4. From the results of this study, we conclude that the inhibitory NANC neurotransmission is mediated by NO alone and does not involve ATP in the portal vein of Japanese White rabbits under our experimental conditions.

Differential effects of extracellular Mg2+ on thrombin-induced and capacitative Ca2+ entry in human coronary arterial endothelial cells

Receptor-mediated and capacitative Ca2+ entry are the primary Ca2+ entry pathways in endothelial cells (ECs). The mechanisms for Ca2+ entry via these pathways have not been fully elucidated. In this study, the effect of low and high external Mg2+ concentrations on these Ca2+ entry pathways was examined in human coronary arterial ECs. External Mg2+ concentration did not affect cytosolic free Mg2+ concentration. After exposure to thrombin in Ca(2+)-free medium, addition of Ca2+ to the medium caused a rise in cytosolic free Ca2+ concentration ([Ca2+]i), indicating thrombin-induced Ca2+ influx. Thrombin-induced Ca2+ influx was inhibited by not only low but also high external Mg2+ concentrations. After depletion of endoplasmic Ca2+ stores by thapsigargin, addition of Ca2+ to the medium induced an increase in [Ca2+]i, indicating capacitative Ca2+ entry. Capacitative entry was found to be accelerated by low external Mg2+ and inhibited by high external Mg2+ concentration. Results suggest that receptor-mediated Ca2+ influx requires external Mg2+ but is inhibited by increased external Mg2+ concentrations and that capacitative Ca2+ entry is reduced by external Mg2+ in human coronary arterial ECs.

Lack of effect of transmembrane gradient of magnesium and sodium on regulation of cytosolic free magnesium concentration in rat lymphocytes

The regulation of the intracellular concentration of Mg2+ ([Mg2+]i) is not fully understood. The level of Mg in lymphocytes is a good predictor of total body Mg status. We measured [Mg2+]i and total Mg in rat lymphocytes by using, respectively, the fluorescent Mg2+ indicator mag-fura-2 and atomic absorption spectrophotometry. The basal [Mg2+]i in rat lymphocytes was 328 +/- 23 micromol/l. An elevation to 5 mmol/l or the removal of extracellular Mg2+ did not affect [Mg2+]i. A reduction in extracellular Na+ did not influence [Mg2+]i for 60 min. The total Mg concentration in lymphocytes also remained stable. Results suggest that the permeability of the plasma membrane to Mg2+ is very low, and that Na+/Mg2+ exchange is not involved in the regulation of [Mg2+]i in rat lymphocytes.