Cavity enhanced liquid-phase stopped-flow kinetics.

The first application of liquid-phase broadband cavity enhanced spectroscopy (BBCEAS) to the measurement of stopped-flow kinetics is reported. The stopped-flow technique is widely used for the study of the kinetics of fast liquid-phase reactions down to millisecond timescales. UV-visible absorption spectroscopy is commonly used as the detection method. Increased sensitivity can potentially allow reactions which are too fast to be measured, to be studied by slowing down the reaction rate through the use of lower concentration of reactants. A simple low cost BBCEAS experimental setup was coupled to a commercial stopped-flow instrument. Comparative standard absorption measurements were also made using a UV-visible double-beam spectrometer as the detector. Measurements were made on the reaction of potassium ferricyanide with sodium ascorbate under pseudo-first order conditions at pH 8 and pH 9.2 A cavity enhancement factor (CEF) of 78 at 434 nm was obtained whilst the minimum detectable change in the absorption coefficient αmin(t), was 1.35 × 10-5 cm-1 Hz-1/2. The kinetic data at pH 9.2 was too fast to be measured using conventional spectroscopy, whilst the BBCEAS measurements allowed 30 fold lower concentration of reactants to be used which slowed down the reaction rate enough to allow the rate constant to be determined. The BBCEAS results showed a 58 fold improvement in sensitivity over the conventional measurements and also compared favourably with the relatively few previous liquid-phase cavity enhanced kinetic studies which have been performed using significantly more complex and expensive experimental setups.

Cavity-Enhanced Immunoassay Measurements in Microtiter Plates Using BBCEAS.

We report on the first detailed use of broadband cavity enhanced absorption spectroscopy (BBCEAS) as a detection system for immunoassay. A vertical R ≥ 0.99 optical cavity was integrated with a motorized XY stage, which functioned as a receptacle for 96-well microtiter plates. The custom-built cavity enhanced microplate reader was used to make measurements on a commercially available osteocalcin sandwich ELISA kit. A 30-fold increase in path length was obtained with a minimum detectable change in the absorption coefficient, αmin(t), of 5.3 × 10(-5) cm(-1) Hz(-1/2). This corresponded to a 39-fold increase in the sensitivity of measurement when directly compared to measurements in a conventional microplate reader. Separate measurements of a standard STREP-HRP colorimetric reaction in microtiter plates of differing optical quality produced an increase in sensitivity of up to 115-fold compared to a conventional microplate reader. The sensitivity of the developed setup compared favorably with previous liquid-phase cavity enhanced studies and approaches the sensitivity of typical fluorometric ELISAs. It could benefit any biochemical test which uses single pass absorption as a detection method, through either the label free detection of biologically important molecules at lower concentrations or the reduction in the amount of expensive biochemicals needed for a particular test, leading to cheaper tests.

Isoproterenol-induced heart failure in the rat is associated with nitric oxide-dependent functional alterations of cardiac function.

AIMS: The role of nitric oxide (NO) in heart failure (HF) is complex and remains controversial. We tested the hypothesis that the role of NO in isolated atria and cardiomyocytes is altered in isoproterenol-induced HF. METHODS AND RESULTS: Rats received isoproterenol (ISO, 5 mg/kg/day, intraperitoneally) or vehicle for 1 week. Haemodynamic parameters were obtained by left ventricular catheterization. Effects of NOS inhibition on isolated atria and on electrically paced left ventricular myocytes were determined. Additionally, expressions of nitric oxide synthases and their allosteric modulators hsp90, caveolin-1, and caveolin-3 proteins in the left ventricles were measured. ISO increased left ventricular mass by 33% and decreased indices of left ventricular systolic and diastolic function dp/dtmin and dp/dtmax (both P<0.05). Isolated atria from HF rats had a lower spontaneous beating rate (P<0.05). NOS inhibition by L-NAME increased basal frequency and attenuated the positive chronotropic effect of beta-adrenergic stimulation in the HF group (P<0.05). Ventricular myocytes from failing hearts had impaired cell shortening. L-NAME decreased contractility of control, but not failing myocytes. Left ventricular expressions of eNOS, hsp90, iNOS, but not nNOS or caveolins, were increased. CONCLUSION: Despite the increased capacity for NO synthesis in isoproterenol-induced HF, NO does not sustain contractility of failing myocytes. NO may contribute to the decreased basal heart rate and it may accelerate beta-adrenergic stimulation of chronotropy.

Rapid large artery remodeling following the administration and withdrawal of calcium channel blockers in spontaneously hypertensive rats.

Chronic treatment with several antihypertensive agents, including calcium channel blockers, may interfere with remodeling of large arteries and increased arterial stiffness. We hypothesize that even a short, seven-day administration of calcium channel blockers might alter an aortic remodeling in spontaneously hypertensive rat (SHR). Male SHR and normotensive WKY rats (n=14 each) were treated by either vehicle, vasculoselective calcium channel blocker nifedipine (1mg/kg/day) or cardiac/vascular calcium channel blockers diltiazem (5mg/kg/day) or verapamil (4 mg/kg/day, n=6 for each treatment) subcutaneously twice daily for seven days. Additional SHR rats were randomized for termination 24, 72 or 120 h (n=5 each) after the withdrawal of nifedipine. Systolic blood pressure was measured by tail cuff and thoracic aorta was collected for histomorphometric and functional analysis including acetylcholine-induced endothelium-dependent relaxation. Seven-day administration of diltiazem and nifedipine, but not verapamil decreased blood pressure in SHR. All drugs significantly attenuated abnormal aortic wall thickness, cross-sectional area and media-to-lumen ratio, but only nifedipine improved impaired endothelium-dependent relaxation. Following the withdrawal of nifedipine, all measured parameters returned back to control SHR values within 72 h. Seven-day treatment with distinct calcium channel blockers attenuates hypertensive remodeling of aorta, which might be, in case of nifedipine, reactivated even by a very short withdrawal of the drug. Therefore, vasculoprotection by calcium channel blockers is not restricted to a prolonged blood pressure modulation, but occurs rapidly. These findings could be relevant for an intervention in augmented vascular stiffness and related cardiovascular risk.