Intermyofilament dynamics of myocytes revealed by second harmonic generation microscopy.

Drosophila melanogaster larva myocytes are imaged with second harmonic generation (SHG) microscopy undergoing forced stretching and rhythmic contractions to determine the nature of the SHG signal. During stretching, double peaked SHG profiles of the anisotropic (A-) bands evolve into single peaks with a higher SHG intensity. The dip in the intensity profile at the center of the A-band is attributed to destructive interference from out-of-phase second harmonic radiating myosin molecules that, in the central region of myofilaments, are arranged antiparallel. An intensity increase at the center of the A-band appears during forced stretching due to a small, less than 100 nm, intermyofilament separation of the antiparallel myosin molecules leading to constructive interference of the SHG radiation. In addition, the same phenomenon occurs during periodic contractions of the myocyte, where an SHG intensity increase with the lengthening of sarcomeres is observed. The SHG intensity dependence on sarcomere length can be used for imaging myocyte contractions with low resolution microscopy, and can be applied for the development of diagnostic tools where monitoring of muscle contraction dynamics is required.

Visualization of mitochondria in cardiomyocytes by simultaneous harmonic generation and fluorescence microscopy.

The simultaneous detection of third harmonic (THG), and multiphoton excitation fluorescence (MPF) or second harmonic (SHG) from the same focal volume has led us to the development of a nonlinear multimodal microscopic biological imaging tool. The multimodal microscope has been applied for imaging of isolated live cardiomyocytes, and investigation of structural origin of the THG and SHG signals has been performed. By employing the different image contrast mechanisms, differentiation of structures inside a single live adult rat cardiomyocyte has been achieved. Based on structural crosscorrelation image analysis between NAD(P)H fluorescence and THG, and morphology of cardiomyocytes we were able to assign large part of the structure revealed by THG to the mitochondria. The crosscorrelation of THG with fluorescence of tetramethylrhodamine methyl ester (TMRM) labeled cardiomyocytes confirmed the mitochondrial origin of THG. The SHG generated structures were anticorrelated with THG and possessed the characteristic pattern of the myofibrils in the myocyte in accordance with the literature. Possible visualization of mitochondria with THG microscopy appeared due to enhancement of the third harmonic by multilayer arrangement of cristae.

The pharmacokinetics and safety of single escalating oral doses of eletriptan.

The pharmacokinetics, safety, and tolerability of the 5-HT(1B/1D) agonist eletriptan were characterized in a randomized, double-blind, placebo-controlled, dose escalation study. Healthy males received single oral doses of 10 to 120 mg. Following screening and baseline measurements, plasma and saliva eletriptan concentrations were measured at intervals over 48 hours and 24 hours, respectively. Samples were analyzed using high-performance liquid chromatography with ultraviolet detection. Both the maximum plasma concentration and the area under the plasma eletriptan concentration-time curve showed an essentially linear relationship to the administered dose. Eletriptan exhibited a median time to maximum plasma concentration of 1 to 1.25 hours and a mean elimination half-life of 3.6 to 7.0 hours. Mean salivary-plasma ratios for pharmacokinetic parameters generally remained constant across the 30 to 90 mg dose range. Eletriptan was well tolerated, with mostly mild and transient adverse events. In conclusion, oral doses of eletriptan in the therapeutic range were rapidly absorbed and exhibited essentially linear plasma and saliva pharmacokinetics.

Influence of semicrystalline order on the second-harmonic generation efficiency in the anisotropic bands of myocytes.

The influence of semicrystalline order on the second-harmonic generation (SHG) efficiency in the anisotropic bands of Drosophila melanogaster sarcomeres from larval and adult muscle has been investigated. Differences in the semicrystalline order were obtained by using wild-type and mutant strains containing different amounts of headless myosin. The reduction in semicrystalline order without altering the chemical composition of myofibrils was achieved by observing highly stretched sarcomeres and by inducing a loss of viability in myocytes. In all cases the reduction of semicrystalline order in anisotropic bands of myocytes resulted in a substantial decrease in SHG. Second-harmonic imaging during periodic contractions of myocytes revealed higher intensities when sarcomeres were in the relaxed state compared with the contracted state. This study demonstrates that an ordered semicrystalline arrangement of anisotropic bands plays a determining role in the efficiency of SHG in myocytes.