DNA Fluorescence

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Femtosecond fluorescence studies of DNA/RNA constituents

International audienceIn this overview, femtosecond fluorescence studies of various DNA constituents are presented, ranging from the monomeric chromophores to different model helices. In order to interpret the experimental results in terms of fundamental processes on the molecular scale they are discussed in the light of recent theoretical calculations. The ultrafast fluorescence decay observed for the monomers is explained by the involvement of highly efficient conical intersections (CI) between the first singlet excited state and the ground state. For the model helices, the picture is more complex, but fluorescence anisotropy data reveal collective effects

Assessing solvent effects on the singlet excited state lifetime of uracil derivatives: a femtosecond fluorescence upconversion study in alcohols and D2O

The excited state lifetimes of uracil, thymine and 5-fluorouracil have been measured using femtosecond UV fluorescence upconversion in various protic and aprotic polar solvents. The fastest decays are observed in acetonitrile and the slowest in aqueous solution while those observed in alcohols are intermediate. No direct correlation with macroscopic solvent parameters such as polarity or viscosity is found, but hydrogen bonding is one key factor affecting the fluorescence decay. It is proposed that the solvent modulates the relative energy of two close-lying electronically excited states, the bright ΠΠ and the dark nΠ states. This relative energy gap controls the non-radiative relaxation of the ΠΠ state through a conical intersection close to the Frank-Condon region competing with the ultrafast internal conversion to the ground state. In addition, an inverse isotope effect is observed in D2O where the decays are faster than in H2O

Innovative techniques and new insights: studying cardiac ionic currents and action potentials in physiologically relevant conditions

Cardiac arrhythmias are associated with various forms of heart diseases. Ventricular arrhythmias present a significant risk for sudden cardiac death. Atrial fibrillations predispose to blood clots leading to stroke and heart attack. Scientists have been developing patch-clamp technology to study ion channels and action potentials (APs) underlying cardiac excitation and arrhythmias. Beyond the traditional patch-clamp techniques, innovative new techniques were developed for studying complex arrhythmia mechanisms. Here we review the recent development of methods including AP-Clamp, Dynamic Clamp, AP-Clamp Sequential Dissection, and Patch-Clamp-in-Gel. These methods provide powerful tools for researchers to decipher how the dynamic systems in excitation-Ca2+ signaling-contraction feedforward and feedback to control cardiac function and how their dysregulations lead to heart diseases.Las arritmias cardiacas están asociadas a diferentes tipos de enfermedad cardiaca. Las arritmias ventriculares constituyen un alto riesgo de muerte súbita. La fibrilación auricular predispone a coágulos sanguíneos que pueden producir accidentes cerebrovasculares e infarto miocárdico. Los científicos han desarrollado la técnica de patch-clamp para estudiar los canales iónicos y los potenciales de acción (PAs), que constituyen la base de la excitación y las arritmias cardiacas. Además de las clásicas técnicas de patch-clamp, se desarrollaron técnicas innovativas para estudiar los mecanismos complejos de las arritmias. En este trabajo, describimos diferentes métodos recientemente desarrollados tales como AP-clamp (“clampeo” del PA), Dynamic Clamp (“clampeo” dinámico), AP-Clamp Sequential Dissection, (disección secuencial del “clampeo” del AP), y Patch-Clamp-in-Gel (Patch clamp en gel). Estos métodos constituyen herramientas poderosas para descifrar cómo los sistemas dinámicos que constituyen la excitación-las señales de Ca2+ y la contracción, se retroalimentan para controlar la función cardiaca y cómo sus alteraciones llevan a la enfermedad cardiaca.Sociedad Argentina de Fisiologí

Altered thermoregulatory responses to clonidine in streptozotocin-diabetic rats

1 The effects of streptozotocin (STZ) treatment on alpha(2)-adrenoceptor regulation of body temperature were studied by monitoring the response of colonic temperature to administration of clonidine. 2 A dose-dependent fall in colonic temperature occurred in control rats given clonidine challenge (0.05-2.0 mg kg(-1), s.c.); this response was inhibited by prior administration of either yohimbine or idazoxan (2 mg kg(-1), s.c.) but not by the peripherally-acting alpha(2)-adrenoceptor antagonist L-659,066 (10 mg kg(-1), s.c.). 3 In rats treated with STZ (65 mg kg(-1), i.v.) administration of clonidine elicited a dose-independent hyperthermia (circa 1 degrees C.); this effect was unaltered by prior administration of yohimbine or idazoxan. 4 Naloxone (5 mg kg(-1), s.c.) elicited a small fall in temperature (< 1 degrees C.) in both control and STZ-treated rats; naloxone pretreatment did not alter the temperature response to clonidine in either group. 5 Nicotinic acid (10 mg kg(-1), s.c.) caused a similar small elevation in temperature in both groups. 6 Administration of replacement insulin to STZ-treated rats maintained weight gain and low blood glucose while the thermoregulatory response to clonidine slowly reverted to normal. 7 These results show that altered central temperature control is an element of the generalised abnormality of alpha(2)-receptor function induced by STZ