Analysis of femtosecond laser-induced cell signaling

Abstract

The interaction of photons with biological tissue results in scattering, reflection, transmission, and absorption. Absorption of photon energy by cells or tissue can evoke photothermal, photomechanical, and photochemical effects, depending on the density of the deposited energy. The femtosecond-pulsed lasers have a high intensity due to the short pulse duration, despite its low average energy. Through nonlinear absorption, femtosecond-pulsed lasers can deliver very high peak energy into the submicron focus area without causing collateral damage. Recently, there have been many reports that femtosecond-pulsed laser can modulate intracellular Ca2+ concentration or biological functions, however the molecular mechanisms are still unclear. In this project, I investigated femtosecond laser-induced cell signaling how femtosecond laser occurs intracellular Ca2+ increases and modulates biological functions at tissue scale. I also performed analysis of femtosecond laser-induced cytotoxicity and its application. After brief introduction of this thesis and recent biological applications of femtosecond laser in chapter 1, I investigated mechanisms of femtosecond laser-induced intracellular Ca2+ increase and propagation in mice urinary smooth muscle tissue and cells in chapter 2. Focused femtosecond-pulsed laser irradiation using high numerical aperture objective lens induces a bunch of free electron, which can be readily converted to reactive oxygen species (ROS) and related free radicals in the localized region. I showed that laser-induced ROS are involved in initial step of Ca2+ releasing from endoplasmic reticulum. Locally increased intracellular Ca2+ levels are amplified by calcium-induced calcium releasing mechanisms through the ryanodine receptor, a Ca2+ channel of the endoplasmic reticulum. The laser-induced Ca2+ increases propagate to adjacent cells through gap junctions. Thus, femtosecond-pulsed lasers can induce smooth muscle contraction by controlling Ca2+, even ...