Can the light-addressable potentiometric sensor (LAPS) detect extracellular potentials of cardiac myocytes?

The light-addressable potentiometric sensor (LAPS) measures localized photo-induced currents from a silicon wafer, which are dependent on the local surface potential and on the intensity of the light pointer. In this study the ability of the LAPS to record extracellular potentials of adherent cells was investigated. Time dependent LAPS photocurrent signals that correlated in time with contractions were recorded from beating cardiac myocytes cultured on LAPS surfaces. Signals could be recorded both when the LAPS was biased to working points where the photocurrent was maximally sensitive to potential changes and when it was biased to working points where the photocurrent was insensitive to changes in surface potential. Therefore, signals could not be predominantly created by changes in extracellular potential and might be related to mechanical contractions. One possible explanation might be, that the cell-induced modulation of photocurrents arose as a result of cell shape changes. Such alterations in cell shape might have focused and defocused the light pointer and, thus, modulated its intensity. To further test this hypothesis, height changes of beating cardiac myocytes were measured with an atomic force microscope (AFM). They were found to match well with signals derived from LAPS measurements. Therefore, it can be concluded, that LAPS signals were mainly determined by the periodic changes in shape of beating heart cells, and this interference precludes the measurements of extracellular electrophysiological potentials from these cells.

Transgenic mice overexpressing alpha2A-adrenoceptors in pancreatic beta-cells show altered regulation of glucose homeostasis

AIMS/HYPOTHESIS

To study the role of the human alpha2A-adrenoceptor in the regulation of insulin secretion and the maintenance of glucose homeostasis in transgenic mice overexpressing this receptor in pancreatic beta cells.

METHODS

A human insulin promoter/human alpha2C10-adrenoceptor chimeric gene was microinjected into mouse embryos and transgenic mice were obtained.

RESULTS

Analysis by RT-PCR showed that the expression of the transgene was restricted to pancreatic islets. Study of the binding of the alpha2-antagonist [3H]RX821002 to membrane preparations showed that islets from transgenic mice had ninefold higher alpha2-adrenoceptor density than those from controls. Immunohistological analysis showed, however, no change in the number or size of islets between control and transgenic mice. Transgenic animals had normal glycaemia and insulinaemia in basal conditions but greater hyperglycaemic and hypoinsulinaemic responses after injection of the alpha2-agonist, UK14304. The lower blood insulin concentration detected in transgenic mice was a reflection of a stronger inhibitory effect of the alpha2-agonist on glucose-stimulated insulin secretion in transgenic islets than in controls. Furthermore, transgenic mice did not have lower glycaemia to basal values after an intraperitoneal glucose tolerance test. This defect was abolished by treatment with the alpha2-adrenoceptor antagonist, RX821002.

CONCLUSION/INTERPRETATION

These results provide evidence in vivo that overexpression of alpha2-adrenoceptors in beta cells can lead to impaired insulin secretion and glucose intolerance.

Dimethylarsinic acid treatment alters six different rat biochemical parameters: relevance to arsenic carcinogenesis

In a previous study, we found that sodium arsenite increased hepatic ornithine decarboxylase (ODC) activity and hepatic heme oxygenase (HO) activity, but did not cause any DNA damage in adult female rat liver or lung, suggesting that arsenite may be a promoter of carcinogenesis. In this study sodium arsenate, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) were administered orally in equitoxic doses to adult female rats at 21 and 4 h prior to sacrifice. DNA damage (DD), cytochrome P450 content (P450), glutathione content (GSH), ODC, serum alanine aminotransferase (ALT) and HO were measured in liver and/or lung tissue. At 60 mg/kg in rat liver, sodium arsenate increased hepatic HO fivefold. MMA decreased ALT at 226 mg/kg, decreased ALT and GSH at 679 mg/kg and also increased P450 at 679 mg/kg in rat liver. DMA decreased ALT and hepatic GSH and increased hepatic HO at 387 mg/kg. In the lung, DMA decreased ODC at both 129 and 387 mg/kg. DD in lung tissue was significantly higher at 387 mg/kg DMA, demonstrating organ specific DNA damage. The biochemical effects and the inferred oncologic potential of the four major forms of arsenic (arsenate, arsenite, MMA and DMA) differ dramatically. The inorganic forms (arsenate and arsenite) are similar to each other (both good HO inducers); the methylated organic forms of arsenic (MMA and DMA) also share a similar pattern of biochemical effects (decreased GSH and ALT, increased P450). All six of the biochemical parameters studied were altered by DMA in either rat liver or lung.

Transgenic mice overexpressing insulin-like growth factor-II in beta cells develop type 2 diabetes

During embryonic development, insulin-like growth factor-II (IGF-II) participates in the regulation of islet growth and differentiation. We generated transgenic mice (C57BL6/SJL) expressing IGF-II in beta cells under control of the rat Insulin I promoter in order to study the role of islet hyperplasia and hyperinsulinemia in the development of type 2 diabetes. In contrast to islets from control mice, islets from transgenic mice displayed high levels of IGF-II mRNA and protein. Pancreases from transgenic mice showed an increase in beta-cell mass (about 3-fold) and in insulin mRNA levels. However, the organization of cells within transgenic islets was disrupted, with glucagon-producing cells randomly distributed throughout the core. We also observed enhanced glucose-stimulated insulin secretion and glucose utilization in islets from transgenic mice. These mice displayed hyperinsulinemia, mild hyperglycemia, and altered glucose and insulin tolerance tests, and about 30% of these animals developed overt diabetes when fed a high-fat diet. Furthermore, transgenic mice obtained from the N1 backcross to C57KsJ mice showed high islet hyperplasia and insulin resistance, but they also developed fatty liver and obesity. These results indicate that local overexpression of IGF-II in islets might lead to type 2 diabetes and that islet hyperplasia and hypersecretion of insulin might occur early in the pathogenesis of this disease.

Candesartan Cilexetil, a Novel Angiotensin II Antagonist, Provides Dose-dependent Antihypertensive Effect with Maintained Tolerability

Candesartan is a new angiotensin II type 1 (AT 1 ) receptor blocker that binds tightly to and dissociates slowly from the AT 1 -receptor. It is administered as a prodrug, candesartan cilexetil, which is completely converted to the active compound, candesartan, during absorption in the gastrointestinal tract. Placebo-controlled studies have shown that candesartan cilexetil is an effective antihypertensive drug. The individual studies, however, lacked the statistical power to assess the dose-response relationship with high precision. A more precise estimate of the effect of different doses may be achieved by pooling similar studies in a meta-analysis. The primary objective of this meta-analysis was to determine the dose-response relationship for the antihypertensive effect of candesartan cilexetil. Six European randomized, double-blind, placebo-controlled, dose-response studies with candesartan cilexetil were reported by 30 September 1996. These studies enrolled similar patients (primary hypertension with a sitting diastolic blood pressure [DBP] of 95-114 mmHg after a placebo run-in period) and had a similar design (parallel groups and fixed doses). The doses investigated ranged from 2 to 16 mg once daily. All doses were not given in every study, but all studies investigated at least two different doses of candesartan cilexetil. The duration of the double-blind phase varied between studies, but was at least 4 weeks (range: 4-12 weeks). The variable of primary interest was sitting DBP measured 24 h after dose (trough effect). Each dose of candesartan was analysed separately, and compared with placebo data only from those studies in which that dose was given. The analysis was performed using an analysis of covariance model. Placebo-corrected estimated mean blood pressure reductions from baseline (randomization) to the end of the study and the 95% confidence intervals for the true mean reductions were calculated for each dose. In total, 1498 hypertensive patients were randomized, of whom 1482 provided efficacy data and were included in the analysis. The vast majority of patients (99%) were of Caucasian origin. The placebo-corrected reductions in sitting DBP and sitting systolic blood pressure (SBP) achieved with the different doses of candesartan cilexetil are shown in the Table. Reductions in blood pressure were dose-related, and age or gender did not influence the antihypertensive effect of candesartan cilexetil. Furthermore, blood pressure reductions achieved in the standing position were similar to those in the sitting position, i.e. there was no indication of an abnormal orthostatic response during treatment with candesartan cilexetil. Heart rate was not significantly influenced by candesartan cilexetil. Adverse events occurred in a similar proportion of patients treated with placebo or candesartan cilexetil and did not increase with the dose. Candesartan cilexetil was equally well tolerated in young and elderly patients and in men and women. Thus, in European patients with mild to moderate hypertension, candesartan cilexetil provides a clinically significant, dose-dependent, antihypertensive effect in doses ranging from 4 to 16 mg once daily. The optimal maintenance doses of candesartan cilexetil appear to be 8 or 16 mg once daily in most patients.

Improvement in exercise tolerance and symptoms of congestive heart failure during treatment with candesartan cilexetil. Symptom, Tolerability, Response to Exercise Trial of Candesartan Cilexetil in Heart Failure (STRETCH) Investigators

BACKGROUND

The renin-angiotensin system plays an important part in the pathogenesis of congestive heart failure (CHF). This study evaluated the effect of an angiotensin II type 1 receptor antagonist on exercise tolerance and symptoms of CHF.

METHODS AND RESULTS

In this multicenter, double-blind, parallel-group study, 844 patients with CHF were randomized to 12 weeks' treatment with placebo (n=211) or candesartan cilexetil 4 mg (n=208), 8 mg (n=212), or 16 mg (n=213) after a 4-week placebo run-in period. Changes in exercise time, Dyspnea Fatigue Index score, NYHA functional class, and cardiothoracic ratio were determined. Candesartan cilexetil produced a dose-related improvement in exercise time. For the intention-to-treat population, the increase produced by candesartan cilexetil 16 mg was significantly greater than that produced by placebo (47.2 versus 30.8 seconds, P=0.0463). All doses of candesartan cilexetil significantly improved the Dyspnea Fatigue Index score relative to placebo. NYHA class improved more frequently in the candesartan cilexetil groups; the differences relative to placebo were not significant. The decrease in cardiothoracic ratio with candesartan 4 to 16 mg was small but statistically significant compared with placebo (all P<0.05). In all candesartan cilexetil groups, plasma renin activity and angiotensin II levels increased from baseline and aldosterone levels decreased in the 8- and 16-mg treatment groups. Candesartan cilexetil was well tolerated at all doses.

CONCLUSIONS

In summary, treatment with candesartan cilexetil demonstrated significant improvements in exercise tolerance, cardiothoracic ratio, and symptoms and signs of CHF and was well tolerated.

[Anesthesia consultation in cardiovascular and thoracic surgery. A survey of patient and physician satisfaction]

OBJECTIVE

To assess the quality of the preadmission anaesthetic consultation prior to cardiovascular and thoracic surgery with a satisfaction inquiry.

STUDY DESIGN

Prospective study with a questionnaire, extended over a period of two months.

PERSONS

Patients and anaesthetists of the cardiothoracic surgical service.

METHODS

The inquiry, which took place after completion of the consultation was achieved by a person non member of the staff. Anaesthetists were questioned on the medical content, its exhaustive character and its value for the patient's perioperative care.

RESULTS

Out of the 273 patients included in the study, 121 agreed to answer the questionnaire. Participation in the study was more significant in older patients (58 +/- 20 vs 51 +/- 24 years) and following shorter waiting time (WT) [15 +/- 13 (0-60) vs 25 +/- 18 (0-66) min]. The duration of the consultation (DC) was not different between the two groups [29 +/- 12 (8-70) vs 31 +/- 14 (6-75) min]. However patients' participation increased when the DC exceeded by 0.6 the sum of DC and WT [DC > 0.6 (DC + WT)]. The analogic score (AS) assessing reduction in preoperative anxiety was 8.4 +/- 1.5 (2-10). Finally, 108 patients out of 121 considered to have been well informed about the anaesthetic [AS = 8.7 +/- 1.2 (4-10)], 113 considered the preadmission consultation as a useful procedure [AS = 8.6 +/- 1.5 (2-10)]) and for 41 a personalized follow-up by the same anaesthetist was valuable. Only three operations had to be postponed the day before surgery. One third of the anaesthetists considered that the consultation improved the clinical and therapeutic management of the patients.

CONCLUSION

This inquiry showed that the preadmission anaesthesia consultation was considered as benefitful by patients and anaesthetists. However the participation of patients in this study was poor. Subsequently to the inquiry information forms have been produced and handed to the patient prior to the consultation.

Simultaneous monitoring of argatroban and its major metabolite using an HPLC method: potential clinical applications

Argatroban is a peptidomimetic inhibitor of thrombin that is currently undergoing extensive clinical trials as a heparin substitute for thrombotic complications. Argatroban is readily metabolized into a major derivative, M1, that has pharmacological characteristics distinct from its parent compound. The currently available clot-based assays measure the cumulative anticoagulant effect of argatroban and its metabolite(s). Available HPLC methods do not differentiate between argatroban and M1-metabolite. A modified method was developed to simultaneouly quantitate M1-metabolite and argatroban in biological fluids. Initial validation studies for the method included clinical trials of argatroban in patients with heparin-induced thrombocytopenia, (ARG 911 Study) and coronary interventional procedures (ARG 310 Study). Plasma samples were extracted with acetonitrile and reconstituted in a mobile phase. Calibration curves were prepared by running known standards of argatroban and M1-metabolite in normal human plasma. Ultraviolet detection was made at 320 nm. The retention times for argatroban and M1-metabolite peaks were found to be 10.5 +/- 0.3 minutes and 3.9 +/- 0.1 minutes, respectively. The extraction efficiency was > 95% (r2 = 0.99). In heparin-induced thrombocytopenia patients with major bleeding complications (n = 30), the relative increase in M1-metabolite compared to argatroban varied widely (two- to eight-fold). The mean concentration of argatroban during the steady infusion period was found to be 0.7 +/- 0.35 microgram/mL, and for M1-metabolite, it was 5.5 +/- 2.8 micrograms/mL. Proportionate results were not seen when higher dosages of argatroban were administered (coronary angioplasty studies). Argatroban and M1-metabolite levels also compared well with the results in global clotting assays. Owing to the simultaneous quantitation of argatroban and M1-metabolite, this method provides a rapid assessment of the pharmacokinetics and pharmacodynamics of argatroban. The differential quantitation may be useful in the assessment of relative metabolic turnover of argatroban that can be related to the hepatic and renal functions in a given patient.

Structure elucidation of the adducts formed by fjord region Dibenzo[a,l]pyrene-11,12-dihydrodiol 13,14-epoxides with deoxyguanosine

(+/-)-anti-Dibenzo[a,l]pyrene-11,12-dihydrodiol 13,14-epoxide {(+/-)-anti-DB[a,l]PDE} was reacted with deoxyguanosine (dG) in dimethylformamide at 100 degrees C for 30 min, and two sets of adducts were isolated: a mixture of (+/-)-anti-cis- & -trans-N(2)dG (43%) and a mixture of (+/-)-anti-cis- & -trans-N7Gua (45%). Both are mixtures of four stereoisomers that cannot be separated by HPLC. Similarly, (+/-)-syn-DB[a,l]PDE was reacted with dG under the same conditions, and (+/-)-syn-cis- & -trans-N(2)dG (38%) and (+/-)-syn-cis- & -trans-N7Gua (59%) were obtained. The structures of the adducts were determined by a combination of NMR and fast atom bombardment mass spectrometry. By reacting (-)-anti-DB[a,l]PDE or (+)-syn-DB[a,l]PDE with dG under the same conditions, however, optically pure N(2)dG and N7Gua isomers were obtained: (-)-anti-cis-N(2)dG (12%), (-)-anti-trans-N(2)dG (17%), (-)-anti-trans-N7Gua (43%), (+)-syn-cis-N(2)dG (7%), (+)-syn-trans-N(2)dG (3%), (+)-syn-cis-N7Gua (36%), and (+)-syn-trans-N7Gua (22%). The structures of the optically pure adducts were assigned by NMR. syn- and anti-DB[a,l]PDE-N(2)dG adducts can be distinguished by fluorescence line-narrowing spectroscopy (FLNS). Moreover, distinction between cis- and trans-stereochemistry of the adducts is also straightforward by FLNS, because the FLN spectra for the four DB[a,l]PDE-N(2)dG adducts, anti-cis, anti-trans, syn-cis, and syn-trans, are spectroscopically unique.

Structure elucidation of the adducts formed by fjord-region Dibenzo[a,l]pyrene 11,12-dihydrodiol 13,14-epoxides and deoxyadenosine

Model adducts to be used in the identification of biologically formed adducts were synthesized by reaction of fjord-region dibenzo[a,l]pyrene 11,12-dihydrodiol 13,14-epoxides (DB[a,l]PDE) and deoxyadenosine (dA). The (+/-)-anti-DB[a,l]PDE was reacted with dA in dimethylformamide at 100 degrees C for 30 min to give four DB[a, l]PDE-14-N(6)dA adducts: (-)-anti-trans (26%), (+)-anti-trans (26%), (-)-anti-cis (17%), and (+)-anti-cis (17%). The (+/-)-syn-DB[a,l]PDE was reacted with dA under the same conditions to yield four DB[a, l]PDE-14-N(6)dA adducts and one N7Ade adduct: (+)-syn-cis (19%), (+)-syn-trans (13%), (-)-syn-cis (19%), (-)-syn-trans (13%), and (+/-)-syn-DB[a,l]PDE-14-N7Ade (22%). The structures of the eight stereoisomers of DB[a,l]PDE-14-N(6)dA were unequivocally assigned by reacting optically pure (-)-anti-DB[a,l]PDE and (+)-syn-DB[a,l]PDE with dA and by a combination of NMR, circular dichroism, and fast atom bombardment mass spectrometry. Reactions at 100 degrees C yielded mainly the trans-opened adducts at the benzylic C-14 position for both (+/-)-anti-DB[a,l]PDE and (-)-anti-DB[a,l]PDE, whereas (+/-)-syn-DB[a,l]PDE and (+)-syn-DB[a,l]PDE afforded mainly cis-opened adducts. At room temperature, however, only trans-opened adducts were obtained from (+/-)-anti-DB[a,l]PDE and only cis-opened adducts from (+/-)-syn-DB[a,l]PDE. Steric hindrance created by the fjord region may be an important factor for the stereoselectivity observed at room temperature.

Severe morbidity after coronary artery surgery: development and validation of a simple predictive clinical score

AIMS

To develop a predictive clinical risk score of post-operative morbidity after coronary artery bypass grafting.

METHODS AND RESULTS

Data were collected retrospectively from 679 patients undergoing emergency or planned bypass surgery between 1 January and 31 December 1996. The incidence of morbidity was 23%. Multivariate stepwise logistic regression analysis on two-thirds of the patients identified eight independent risk factors for severe morbidity. Six of these were pre-operative: symptomatic right heart failure, previous ventricular arrhythmias, previous coronary bypass surgery, chronic pulmonary disease, ST changes on pre-operative electrocardiogram, body mass index <24 kg. m-2, and two were intra-operative factors: the surgeon who operated, and the cardiopulmonary bypass time. A predictive clinical risk score was developed with the six pre-operative risk factors. The negative predictive value of the model is 87% and the area under the receiver operating characteristic curve is 0.77. When tested on the remaining patients not used for developing the model, the area under the curve is 0.65.

CONCLUSION

This pre-operative risk score provides a simple method of risk stratification for patients undergoing coronary artery surgery. However, as for all predictive models, the performance of the score decreases when applied to a population other than that used to develop it.

Mapping the mechanical pulse of single cardiomyocytes with the atomic force microscope

The atomic force microscope (AFM) was used to analyse the contractile behaviour of embryonic chicken cardiomyocytes. The mechanical pulsing of cardiomyocytes was analysed by observing active single cells as well as cells in a confluent layer. When embedded in a confluent layer, owing to synchronisation, pulsing of the cells was often found to be very stable in terms of frequency and amplitude of the beat, including negative as well as positive amplitudes. Nevertheless, owing to movements of contraction centres within the layer, a flipping of the sign of the amplitude did sometimes also occur on a time scale of minutes. In contrast, single cells often changed between active periods of pulsing and periods of complete quietness. Also characteristic parameters like beat period and pulse amplitude were observed to be unstable. Finally, we combined the abilities of the AFM to image adherent single cells and to record locally beat amplitudes, to characterise the pulsing behaviour of single cells laterally resolved.

Oral and systemic immunoglobulin G-subclass antibodies to Actinobacillus actinomycetemcomitans leukotoxin

Salivary, gingival crevicular fluid and serum-specific immunoglobulin G (IgG)-subclass antibodies to Actinobacillus actinomycetemcomitans leuktoxin were quantified by enzyme-linked immunosorbent assay. Samples were taken from six patients with periodontal pockets > or = 5 mm, harboring A. actinomycetemcomitans in subgingival plaque and from six healthy, sex- and age-matched controls, who did not harbor A. actinomycetemcomitans. In individuals suffering from periodontitis, the median values of specific IgG1- and IgG2-subclass antibodies in saliva, gingival crevicular fluid and serum were, respectively IgG1 147 ng/ml, 5226 ng/ml and 7318 ng/ml and IgG2 4.8 ng/ml, 934 ng/ml and 860 ng/ml. In the patients, specific IgG3 antibodies were detected in one out of six individuals in saliva, in two individuals in gingival crevicular fluid and in five out of six patients in serum with a median value of 561 ng/ml. The median values of specific IgG4 antibodies in saliva, gingival crevicular fluid and serum were below detectable levels. The median values of the total IgG subclasses in saliva and serum were 14622 ng/ml and 10.3 g/l respectively. Individuals with periodontitis had, compared with controls, a higher ratio of specific IgG1 antibodies to total IgG1 in saliva (P < 0.05) and in serum (P < 0.05) and a higher ratio of specific IgG antibodies to total IgG in saliva (P < 0.05) and in serum (P < 0.01). The results show an elevation of both oral and systemic specific antibodies to A. actinomycetemcomitans leukotoxin.

Influence of temperature on tracheal tube cuff pressure during cardiac surgery

BACKGROUND

Lateral wall pressure may cause tracheal injury by affecting tracheal capillary blood flow. Damage to the trachea is less severe when lateral wall pressure exerted by the endotracheal tube cuff does not exceed the mean capillary perfusion pressure of the mucosa. The purpose of this study was to determine the effects of hypothermic and normothermic cardiopulmonary bypass (CPB) on tracheal tube cuff pressure dynamics.

METHODS

Twenty-two patients were studied during normothermic CPB (pulmonary artery blood temperature in the CPB period between 36 and 35 degrees C), and 22 patients during hypothermic CPB (pulmonary artery temperature in the CPB period between 32 and 28 degrees C). A Mallinckrodt Medical Lo-Contour Murphy tracheal tube, with high-volume, low-pressure cuff was used without lubricant. Intracuff pressure (ITCP) was recorded at end-expiration before, during and after cardiopulmonary bypass.

RESULTS

ITCP measurements were different between groups during CPB at aortic cross-clamping (13.9 +/- 0.8 mmHg in the normothermic group versus 11.3 +/- 0.4 mmHg in the hypothermic group, P < 0.05), and respectively during CPB after aortic declamping (15.3 +/- 0.8 mmHg and 12.6 +/- 0.8 mmHg, P < 0.05) and after CPB at the end of surgery (16.8 +/- 0.7 mmHg and 18.6 +/- 0.3 mmHg, P < 0.05).

CONCLUSION

We conclude that the ITCP is higher in normothermic CPB than in hypothermic CPB; however, the clinical significance of this observation needs further investigation.

Electrically excitable normal rat kidney fibroblasts: A new model system for cell-semiconductor hybrids

In testing various designs of cell-semiconductor hybrids, the choice of a suitable type of electrically excitable cell is crucial. Here normal rat kidney (NRK) fibroblasts are presented as a cell line, easily maintained in culture, that may substitute for heart or nerve cells in many experiments. Like heart muscle cells, NRK fibroblasts form electrically coupled confluent cell layers, in which propagating action potentials are spontaneously generated. These, however, are not associated with mechanical disturbances. Here we compare heart muscle cells and NRK fibroblasts with respect to action potential waveform, morphology, and substrate adhesion profile, using the whole-cell variant of the patch-clamp technique, atomic force microscopy (AFM), and reflection interference contrast microscopy (RICM), respectively. Our results clearly demonstrate that NRK fibroblasts should provide a highly suitable test system for investigating the signal transfer between electrically excitable cells and extracellular detectors, available at a minimum cost and effort for the experimenters.