Dynacortin contributes to cortical viscoelasticity and helps define the shape changes of cytokinesis.

During cytokinesis, global and equatorial pathways deform the cell cortex in a stereotypical manner, which leads to daughter cell separation. Equatorial forces are largely generated by myosin-II and the actin crosslinker, cortexillin-I. In contrast, global mechanics are determined by the cortical cytoskeleton, including the actin crosslinker, dynacortin. We used direct morphometric characterization and laser-tracking microrheology to quantify cortical mechanical properties of wild-type and cortexillin-I and dynacortin mutant Dictyostelium cells. Both cortexillin-I and dynacortin influence cytokinesis and interphase cortical viscoelasticity as predicted from genetics and biochemical data using purified dynacortin proteins. Our studies suggest that the regulation of cytokinesis ultimately requires modulation of proteins that control the cortical mechanical properties that establish the force-balance that specifies the shapes of cytokinesis. The combination of genetic, biochemical, and biophysical observations suggests that the cell's cortical mechanical properties control how the cortex is remodeled during cytokinesis.

Hybrid germanium/silica optical fibers for endoscopic delivery of erbium:YAG laser radiation.

BACKGROUND AND OBJECTIVES: Endoscopic applications of the erbium (Er):YAG laser have been limited due to the lack of an optical fiber delivery system that is robust, flexible, and biocompatible. This study reports the testing of a hybrid germanium/silica fiber capable of delivering Er:YAG laser radiation through a flexible endoscope. STUDY DESIGN/MATERIALS AND METHODS: Hybrid optical fibers were assembled from 1-cm length, 550-microm core, silica fiber tips attached to either 350- or 425-microm germanium oxide "trunk" fibers. Er:YAG laser radiation (lambda = 2.94 microm) with laser pulse lengths of 70 and 220 microseconds, pulse repetition rates of 3-10 Hz, and laser output energies of up to 300 mJ was delivered through the fibers for testing. RESULTS: Maximum fiber output energies measured 180+/-30 and 82+/-20 mJ (n = 10) under straight and tight bending configurations, respectively, before fiber interface damage occurred. By comparison, the damage threshold for the germanium fibers without silica tips during contact soft tissue ablation was only 9 mJ (n = 3). Studies using the hybrid fibers for lithotripsy also resulted in fiber damage thresholds (55-114 mJ) above the stone ablation threshold (15-23 mJ). CONCLUSIONS: Hybrid germanium/silica fibers represent a robust, flexible, and biocompatible method of delivering Er:YAG laser radiation during contact soft tissue ablation. However, significant improvement in the hybrid fibers will be necessary before they can be used for efficient Er:YAG laser lithotripsy.

Erbium:YAG laser lithotripsy using hybrid germanium/silica optical fibers.

BACKGROUND AND PURPOSE: Previous studies have demonstrated that the erbium:YAG laser is two to three times more efficient for laser lithotripsy than the holmium:YAG laser. However, the lack of a suitable optical fiber delivery system remains a major obstacle to clinical application of Er:YAG laser lithotripsy. This paper describes the initial testing of a hybrid germanium oxide/silica optical fiber for potential endoscopic use with the Er:YAG laser. MATERIALS AND METHODS: Er:YAG laser radiation with a wavelength of 2.94 microm, a pulse energy of 10 to 600 mJ, a pulse length of 220 microsec, and pulse-repetition rates of 3 to 10 Hz was focused into either 350- or 425- microm-core hybrid germanium/silica fibers in contact with human uric acid or calcium oxalate monohydrate stones. RESULTS: Average Er:YAG pulse energies of 157 +/- 46 mJ (66 J/cm(2)) (N = 8) were delivered at 10 Hz through the 425-microm hybrid fibers in contact with urinary stones before fiber damage was observed. A maximum pulse energy of 233 mJ (98 J/cm(2)) was also measured through the hybrid fiber in contact with the stones. These values are significantly greater than the stone ablation thresholds of 15 to 23 mJ (6-10 J/cm(2)) and the fiber damage thresholds measured for germanium oxide, 18 +/- 1 mJ (13 J/cm(2)), and sapphire, 73 mJ (51 J/cm(2)), optical fibers during Er:YAG laser lithotripsy (P < 0.05). CONCLUSIONS: A prototype hybrid germanium/silica optical fiber demonstrated better performance than both germanium oxide and sapphire fibers for transmission of Er:YAG laser radiation during in vitro lithotripsy.

Transmission of Q-switched erbium:YSGG (lambda=2.79 microm) and erbium:YAG (lambda=2.94 microm) laser radiation through germanium oxide and sapphire optical fibres at high pulse energies.

The erbium:YSGG and erbium:YAG lasers are used for tissue ablation in dermatology, dentistry and ophthalmology. The purpose of this study was to compare germanium oxide and sapphire optical fibres for transmission of sufficient Q-switched erbium laser pulse energies for potential use in both soft and hard tissue ablation applications. Fibre transmission studies were conducted with Q-switched (500 ns) Er:YSGG (lambda=2.79 microm) and Er:YAG (lambda=2.94 microm) laser pulses delivered at 3 Hz through 1-m-long, 450-mum germanium oxide and 425-mum sapphire optical fibres. Transmission of free-running (300 micros) Er:YSGG and Er:YAG laser pulses was also conducted for comparison. Each set of measurements was carried out on seven different sapphire or germanium fibres, and the data were then averaged. Fibre attenuation of Q-switched Er:YSGG laser energy measured 1.3+/-0.1 dB/m and 1.0+/-0.2 dB/m for the germanium and sapphire fibres, respectively. Attenuation of Q-switched Er:YAG laser energy measured 0.9+/-0.3 dB/m and 0.6+/-0.2 dB/m, respectively. A maximum Q-switched Er:YSGG pulse energy of 42 mJ (26-30 J/cm(2)) was transmitted through the fibres. However, fibre tip damage was observed at energies exceeding 25 mJ (n=2). Both germanium oxide and sapphire optical fibres transmitted sufficient Q-switched Er:YSGG and Er:YAG laser radiation for use in both soft and hard tissue ablation. This is the first report of germanium and sapphire fibre optic transmission of Q-switched erbium laser energies of 25-42 mJ per pulse.