Cell Imaging and Manipulation by Nonlinear Optical Microscopy

Calcium Signaling in Cardiomyocyte Function

Rhythmic increases in intracellular Ca²⁺ concentration underlie the contractile function of the heart. These heart muscle-wide changes in intracellular Ca²⁺ are induced and coordinated by electrical depolarization of the cardiomyocyte sarcolemma by the action potential. Originating at the sinoatrial node, conduction of this electrical signal throughout the heart ensures synchronization of individual myocytes into an effective cardiac pump. Ca²⁺ signaling pathways also regulate gene expression and cardiomyocyte growth during development and in pathology. These fundamental roles of Ca²⁺ in the heart are illustrated by the prevalence of altered Ca²⁺ homeostasis in cardiovascular diseases. Indeed, heart failure (an inability of the heart to support hemodynamic needs), rhythmic disturbances, and inappropriate cardiac growth all share an involvement of altered Ca²⁺ handling. The prevalence of these pathologies, contributing to a third of all deaths in the developed world as well as to substantial morbidity makes understanding the mechanisms of Ca²⁺ handling and dysregulation in cardiomyocytes of great importance.

Making a big thing of a small cell--recent advances in single cell analysis

Single cell analysis is an emerging field requiring a high level interdisciplinary collaboration to provide detailed insights into the complex organisation, function and heterogeneity of life. This review is addressed to life science researchers as well as researchers developing novel technologies. It covers all aspects of the characterisation of single cells (with a special focus on mammalian cells) from morphology to genetics and different omics-techniques to physiological, mechanical and electrical methods. In recent years, tremendous advances have been achieved in all fields of single cell analysis: (1) improved spatial and temporal resolution of imaging techniques to enable the tracking of single molecule dynamics within single cells; (2) increased throughput to reveal unexpected heterogeneity between different individual cells raising the question what characterizes a cell type and what is just natural biological variation; and (3) emerging multimodal approaches trying to bring together information from complementary techniques paving the way for a deeper understanding of the complexity of biological processes. This review also covers the first successful translations of single cell analysis methods to diagnostic applications in the field of tumour research (especially circulating tumour cells), regenerative medicine, drug discovery and immunology.

Enhanced sensitivity in dark-field microscopy by optimizing the illumination angle

Dark-field microscopy is a well-known technique used to exclude the bright background of unscattered photons from a measurement. We show that by choosing an appropriate illumination angle, the background of unwanted scattered light can also be suppressed. The collected flux of scattered photons is calculated in the Mie scattering regime for various particle sizes and objectives over a range of illumination angles. In the case that the dark-field measurement is limited by background scattering, we find that the sensitivity can be improved by lowering the objective numerical aperture. The collected photon flux is calculated for an exemplary dark-field microscopy experiment in which lipid granules were studied within yeast cells. Our model suggests that the signal-to-noise ratio was over three-orders-of-magnitude higher than it would have been with an equivalent bright-field setup.

Multimodal optical workstation for simultaneous linear, nonlinear microscopy and nanomanipulation: upgrading a commercial confocal inverted microscope

In this work we propose and build a multimodal optical workstation that extends a commercially available confocal microscope (Nikon Confocal C1-Si) to include nonlinear/multiphoton microscopy and optical manipulation/stimulation tools such as nanosurgery. The setup allows both subsystems (confocal and nonlinear) to work independently and simultaneously. The workstation enables, for instance, nanosurgery along with simultaneous confocal and brightfield imaging. The nonlinear microscopy capabilities are added around the commercial confocal microscope by exploiting all the flexibility offered by this microscope and without need for any mechanical or electronic modification of the confocal microscope systems. As an example, the standard differential interference contrast condenser and diascopic detector in the confocal microscope are readily used as a forward detection mount for second harmonic generation imaging. The various capabilities of this workstation, as applied directly to biology, are demonstrated using the model organism Caenorhabditis elegans.

New techniques in linear and non-linear laser optics in muscle research

This review proposes a brief summary of two applications of lasers to muscle research. The first application (laser tweezers), is now a well-established technique in the field, adopted by several laboratories in the world and producing a constant stream of original data, fundamental for our improved understanding of muscle contraction at the level of detail that only single molecule measurements can provide. As an example of the power of this technique, here we focus on some recent results, revealing the performance of the working stroke in at least two distinct steps also in skeletal muscle myosin. A second laser-based technique described here is second-harmonic generation; the application of this technique to muscle research is very recent. We describe the main results obtained thus far in this area and the potentially remarkable impact that this technology may have in muscle research.